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4 <title>Issues in Cell Configuration and Administration</title>
6 <para>This chapter discusses many of the issues to consider when
7 configuring and administering a cell, and directs you to detailed
8 related information available elsewhere in this guide. It is assumed you
9 are already familiar with the material in <link linkend="HDRWQ5">An
10 Overview of OpenAFS Administration</link>.</para>
12 <para>It is best to read this chapter before installing your cell's
13 first file server machine or performing any other administrative
17 <primary>AFS</primary>
19 <secondary>differences from UNIX summarized</secondary>
23 <primary>UNIX</primary>
25 <secondary>differences from AFS summarized</secondary>
29 <primary>differences</primary>
31 <secondary>between AFS and UNIX, summarized</secondary>
36 <title>Differences between AFS and UNIX: A Summary</title>
38 <para>AFS behaves like a standard UNIX file system in most respects,
39 while also making file sharing easy within and between cells. This
40 section describes some differences between AFS and the UNIX file
41 system, referring you to more detailed information as
45 <primary>protection</primary>
47 <secondary>AFS compared to UNIX</secondary>
50 <sect2 id="Header_35">
51 <title>Differences in File and Directory Protection</title>
53 <para>AFS augments the standard UNIX file protection mechanism in
54 two ways: it associates an <emphasis>access control list
55 (ACL)</emphasis> with each directory, and it enables users to define
56 a large number of their own groups, which can be placed on
59 <para>AFS uses ACLs to protect files and directories, rather than
60 relying exclusively on the mode bits. This has several implications,
61 which are discussed further in the indicated sections:
64 <para>AFS ACLs use seven access permissions rather than the
65 three UNIX mode bits. See <link linkend="HDRWQ567">The AFS ACL
66 Permissions</link>.</para>
70 <para>For directories, AFS ignores the UNIX mode bits. For
71 files, AFS uses only the first set of mode bits (the <emphasis
72 role="bold">owner</emphasis> bits), and their meaning
73 interacts with permissions on the directory's ACL. See <link
74 linkend="HDRWQ580">How AFS Interprets the UNIX Mode
79 <para>A directory's ACL protects all of the files in a
80 directory in the same manner. To apply a more restrictive set
81 of AFS permissions to certain file, place it in directory with
82 a different ACL. If a directory must contain files with
83 different permissions, use symbolic links to point to files
84 stored in directories with different ACLs.</para>
88 <para>Moving a file to a different directory changes its
89 protection. See <link linkend="HDRWQ566">Differences Between
90 UFS and AFS Data Protection</link>.</para>
94 <para>An ACL can include about 20 entries granting different
95 combinations of permissions to different users or groups,
96 rather than only the three UNIX entities represented by the
97 three sets of mode bits. See <link
98 linkend="HDRWQ566">Differences Between UFS and AFS Data
99 Protection</link>.</para>
103 <para>You can designate an AFS file as write-only as in the
104 UNIX file system, by setting only the <emphasis
105 role="bold">w</emphasis> (<emphasis
106 role="bold">write</emphasis>) mode bit. You cannot designate
107 an AFS directory as write-only, because AFS ignores the mode
108 bits on a directory. See <link linkend="HDRWQ580">How AFS
109 Interprets the UNIX Mode Bits</link>.</para>
114 <para>AFS enables users to create groups and add other users to
115 those groups. Placing these groups on ACLs extends the same
116 permissions to a number of exactly specified users at the same time,
117 which is much more convenient than placing the individuals on the
118 ACLs directly. See <link linkend="HDRWQ531">Administering the
119 Protection Database</link>.</para>
121 <para>There are also system-defined groups, <emphasis
122 role="bold">system:anyuser</emphasis> and <emphasis
123 role="bold">system:authuser</emphasis>, whose presence on an ACL
124 extends access to a wide range of users at once. See <link
125 linkend="HDRWQ535">The System Groups</link> and <link
126 linkend="HDRWQ571">Using Groups on ACLs</link>.</para>
129 <primary>authentication</primary>
131 <secondary>AFS compared to UNIX</secondary>
135 <primary>password</primary>
137 <secondary>AFS compared to UNIX</secondary>
142 <title>Differences in Authentication</title>
144 <para>Just as the AFS filespace is distinct from each machine's
145 local file system, AFS authentication is separate from local
146 login. This has two practical implications, which will already be
147 familiar to users and system administrators who use Kerberos for
151 <para>To access AFS files, users must log into the local
152 machine as normal, obtain Kerberos tickets, and then obtain
153 AFS tokens. This process can often be automated through the
154 system authentication configuration so that the user logs into
155 the system as normal and obtains Kerberos tickets and AFS
156 tokens transparently. If you cannot or chose not to configure
157 the system this way, your users must login and authenticate in
158 separate steps, as detailed in the <emphasis>OpenAFS User
159 Guide</emphasis>.</para>
163 <para>Passwords may be stored in two separate places: the
164 Kerberos KDC and, optionally, each machine's local user
165 database (<emphasis role="bold">/etc/passwd</emphasis> or
166 equivalent) for the local system. A user's passwords in the
167 two places can differ if desired.</para>
173 <sect2 id="Header_37">
174 <title>Differences in the Semantics of Standard UNIX
177 <para>This section summarizes how AFS modifies the functionality of
181 <term><emphasis role="bold">The chmod
182 command</emphasis></term>
186 <primary>chmod command</primary>
187 <secondary>AFS compared to UNIX</secondary>
191 <primary>commands</primary>
192 <secondary>chmod (AFS compared to UNIX)</secondary>
196 <primary>setuid programs</primary>
197 <secondary>setting mode bits</secondary>
200 <para>Only members of the <emphasis
201 role="bold">system:administrators</emphasis> group can use
202 this command to turn on the setuid, setgid or sticky mode
203 bits on AFS files. For more information, see <link
204 linkend="HDRWQ409">Determining if a Client Can Run Setuid
205 Programs</link>.</para>
210 <term><emphasis role="bold">The chown
211 command</emphasis></term>
215 <primary>chown command</primary>
216 <secondary>AFS compared to UNIX</secondary>
220 <primary>commands</primary>
221 <secondary>chown (AFS compared to UNIX)</secondary>
224 <para>Only members of the <emphasis
225 role="bold">system:administrators</emphasis> group can issue
226 this command on AFS files.</para>
231 <term><emphasis role="bold">The chgrp
232 command</emphasis></term>
236 <primary>chgrp command</primary>
237 <secondary>AFS compared to UNIX</secondary>
241 <primary>commands</primary>
242 <secondary>chgrp (AFS compared to UNIX)</secondary>
245 <para>Only members of the <emphasis
246 role="bold">system:administrators</emphasis> can issue this
247 command on AFS files and directories.</para>
252 <term><emphasis role="bold">The groups and id
253 commands</emphasis></term>
257 <primary>groups command</primary>
258 <secondary>AFS compared to UNIX</secondary>
262 <primary>id command</primary>
263 <secondary>AFS compared to UNIX</secondary>
267 <primary>commands</primary>
268 <secondary>groups (AFS compared to UNIX)</secondary>
272 <primary>commands</primary>
273 <secondary>id (AFS compared to UNIX)</secondary>
276 <para>If the user's AFS tokens are associated with a process
277 authentication group (PAG), the output of these commands may
278 include one or two large numbers. These are artificial
279 groups used by the OpenAFS Cache Manager to track the PAG on
280 some platforms. Other platforms may use other methods, such
281 as native kernel support for a PAG or a similar concept, in
282 which case the large GIDs may not appear. To learn about
283 PAGs, see <link linkend="HDRWQ64">Identifying AFS Tokens by
289 <term><emphasis role="bold">The ln command</emphasis></term>
293 <primary>ln command</primary>
294 <secondary>AFS compared to UNIX</secondary>
298 <primary>commands</primary>
299 <secondary>ln (AFS compared to UNIX)</secondary>
302 <para>This command cannot create hard links between files in
303 different AFS directories. See <link
304 linkend="HDRWQ32">Creating Hard Links</link>.</para>
309 <term><emphasis role="bold">The sshd daemon and ssh
310 command</emphasis></term>
314 <primary>sshd command</primary>
315 <secondary>AFS compared to UNIX</secondary>
319 <primary>commands</primary>
320 <secondary>sshd (AFS compared to UNIX)</secondary>
324 <primary>ssh command</primary>
325 <secondary>AFS compared to UNIX</secondary>
329 <primary>commands</primary>
330 <secondary>ssh (AFS compared to UNIX)</secondary>
333 <para>In order for a user to have access to files stored in
334 AFS, that user needs to have Kerberos tickets and an AFS token
335 on the system from which they're accessing AFS. This has an
336 implication for users who log in remotely via protocols such
337 as Secure Shell (SSH): that log-in process must create local
338 Kerberos tickets and an AFS token on the system, or the user
339 will have to separately authenticate to Kerberos and AFS
340 after logging in.</para>
342 <para>The <ulink url="http://www.openssh.org/">OpenSSH
343 project</ulink> provides an SSH client and server that uses
344 the GSS-API protocol to pass Kerberos tickets between
345 machines. With a suitable SSH client, this allows users to
346 delegate their Kerberos tickets to the remote machine, and
347 that machine to store those tickets and obtain AFS tokens as
348 part of the log-in process.</para>
355 <primary>fsck command</primary>
357 <secondary>AFS compared to UNIX</secondary>
361 <primary>file server machine</primary>
362 <secondary>inode-based</secondary>
366 <primary>file server machine</primary>
367 <secondary>namei-based</secondary>
371 <primary>namei</primary>
372 <secondary>definition</secondary>
376 <primary>commands</primary>
378 <secondary>fsck (AFS compared to UNIX)</secondary>
382 <primary>fsck command</primary>
384 <secondary>AFS version</secondary>
388 <primary>commands</primary>
390 <secondary>fsck (AFS version)</secondary>
394 <primary>directories</primary>
396 <secondary>lost+found</secondary>
400 <primary>lost+found directory</primary>
404 <sect2 id="Header_38">
405 <title>The AFS version of the fsck Command and inode-based
409 <para>The fileserver uses either of two formats for storing data
410 on disk. The inode-based format uses a combination of regular
411 files and extra fields stored in the inode data structures that
412 are normally reserved for use by the operating system. The namei
413 format uses normal file storage and does not use special
414 structures. The choice of storage formats is chosen at compile
415 time and the two formats are incompatible. The inode format is
416 only available on certain platforms. The storage format must be
417 consistent for the fileserver binaries and all vice partitions on
418 a given file server machine.</para>
422 <para>This section on fsck advice only applies to the inode-based
423 fileserver binaries. On servers using namei-based binaries, the
424 vendor-supplied fsck can be used as normal.</para>
427 <para>If you are using AFS fileserver binaries compiled with the
428 inode-based format, never run the standard UNIX <emphasis
429 role="bold">fsck</emphasis> command on an AFS file server
430 machine. It does not understand how the File Server organizes volume
431 data on disk, and so moves all AFS data into the <emphasis
432 role="bold">lost+found</emphasis> directory on the partition.</para>
434 <para>Instead, use the version of the <emphasis
435 role="bold">fsck</emphasis> program that is included in the AFS
436 distribution. The <emphasis>OpenAFS Quick Start Guide</emphasis>
437 explains how to replace the vendor-supplied <emphasis
438 role="bold">fsck</emphasis> program with the AFS version as you
439 install each server machine.</para>
441 <para>The AFS version functions like the standard <emphasis
442 role="bold">fsck</emphasis> program on data stored on both UFS and
443 AFS partitions. The appearance of a banner like the following as the
444 <emphasis role="bold">fsck</emphasis> program initializes confirms
445 that you are running the correct one:</para>
448 --- AFS (R) version fsck---
451 <para>where <emphasis>version</emphasis> is the AFS version. For
452 correct results, it must match the AFS version of the server
453 binaries in use on the machine.</para>
455 <para>If you ever accidentally run the standard version of the
456 program, contact your AFS support provider, contact the OpenAFS
457 mailing lists, or refer to the <ulink
458 url="http://www.openafs.org/support.html">OpenAFS support web
459 page</ulink> for support options. It is sometimes possible to
460 recover volume data from the <emphasis
461 role="bold">lost+found</emphasis> directory. If the data is not
462 recoverabled, then restoring from backup is recommended.</para>
465 <para>Running the fsck binary supplied by the operating system
466 vendor on an fileserver using inode-based file storage will result
467 in data corruption!</para>
472 <title>Creating Hard Links</title>
475 <primary>hard link</primary>
477 <secondary>AFS restrictions on</secondary>
481 <primary>restrictions</primary>
483 <secondary>on hard links in AFS</secondary>
486 <para>AFS does not allow hard links (created with the UNIX <emphasis
487 role="bold">ln</emphasis> command) between files that reside in
488 different directories, because in that case it is unclear which of
489 the directory's ACLs to associate with the link.</para>
491 <para>AFS also does not allow hard links to directories, in order to
492 keep the file system organized as a tree.</para>
494 <para>It is possible to create symbolic links (with the UNIX
495 <emphasis role="bold">ln -s</emphasis> command) between elements in
496 two different AFS directories, or even between an element in AFS and
497 one in a machine's local UNIX file system. Do not create a symbolic
498 link in AFS to a file whose name begins with either a number sign
499 (<emphasis role="bold">#</emphasis>) or a percent sign (<emphasis
500 role="bold">%</emphasis>), however. The Cache Manager interprets
501 such links as a mount point to a regular or read/write volume,
506 <title>AFS Implements Save on Close</title>
509 <primary>fsync system call</primary>
511 <secondary>for files saved on AFS client</secondary>
515 <primary>close system call</primary>
517 <secondary>for files saved on AFS client</secondary>
521 <primary>write</primary>
523 <secondary>system call for files saved on AFS client</secondary>
526 <para>When an application issues the UNIX <emphasis
527 role="bold">close</emphasis> system call on a file, the Cache
528 Manager performs a synchronous write of the data to the File Server
529 that maintains the central copy of the file. It does not return
530 control to the application until the File Server has acknowledged
531 receipt of the data. For the <emphasis role="bold">fsync</emphasis>
532 system call, control does not return to the application until the
533 File Server indicates that it has written the data to non-volatile
534 storage on the file server machine.</para>
536 <para>When an application issues the UNIX <emphasis
537 role="bold">write</emphasis> system call, the Cache Manager writes
538 modifications to the local AFS client cache only. If the local
539 machine crashes or an application program exits without issuing the
540 <emphasis role="bold">close</emphasis> system call, it is possible
541 that the modifications are not recorded in the central copy of the
542 file maintained by the File Server. The Cache Manager does sometimes
543 write this type of modified data from the cache to the File Server
544 without receiving the <emphasis role="bold">close</emphasis> or
545 <emphasis role="bold">fsync</emphasis> system call, such as when it
546 needs to free cache chunks for new data. However, it is not
547 generally possible to predict when the Cache Manager transfers
548 modified data to the File Server in this way.</para>
550 <para>The implication is that if an application's <emphasis
551 role="bold">Save</emphasis> option invokes the <emphasis
552 role="bold">write</emphasis> system call rather than <emphasis
553 role="bold">close</emphasis> or <emphasis
554 role="bold">fsync</emphasis>, the changes are not necessarily stored
555 permanently on the File Server machine. Most application programs
556 issue the <emphasis role="bold">close</emphasis> system call for
557 save operations, as well as when they finish handling a file and
558 when they exit.</para>
561 <sect2 id="Header_41">
562 <title>Setuid Programs</title>
565 <primary>setuid programs</primary>
567 <secondary>restrictions on</secondary>
570 <para>The UNIX setuid bit is ignored by default for programs run
571 from AFS, but can be enabled by the system administrator on a client
572 machine. The <emphasis role="bold">fs setcell</emphasis> command
573 determines whether setuid programs that originate in a particular
574 cell can run on a given client machine. Running setuid binaries from
575 AFS poses a security risk due to weaknesses in the integrity checks
576 of the AFS protocol and should normally not be permitted. See <link
577 linkend="HDRWQ409">Determining if a Client Can Run Setuid
578 Programs</link>.</para>
580 <para>Set the UNIX setuid bit only for files whose owner is UID 0
581 (the local superuser <emphasis role="bold">root</emphasis>). This
582 does not present an automatic security risk: the local superuser has
583 no special privilege in AFS, but only in the local machine's UNIX
584 file system and kernel. Setting the UNIX setuid bit for files owned
585 with a different UID will have unpredictable resuilts, since that
586 UID will be interpreted as possibly different users on each AFS
587 client machine.</para>
589 <para>Any file can be marked with the setuid bit, but only members
590 of the <emphasis role="bold">system:administrators</emphasis> group
591 can issue the <emphasis role="bold">chown</emphasis> system call or
592 the <emphasis role="bold">chown</emphasis> command, or issue the
593 <emphasis role="bold">chmod</emphasis> system call or the <emphasis
594 role="bold">chmod</emphasis> command to set the setuid bit.</para>
599 <title>Choosing a Cell Name</title>
602 <primary>cell</primary>
604 <secondary>name</secondary>
606 <tertiary>choosing</tertiary>
610 <primary>choosing</primary>
612 <secondary>name</secondary>
614 <tertiary>cell</tertiary>
618 <primary>conventions</primary>
620 <secondary>cell name</secondary>
624 <primary>Internet</primary>
626 <secondary>conventions for cell name</secondary>
629 <para>This section explains how to choose a cell name and explains why
630 choosing an appropriate cell name is important.</para>
632 <para>Your cell name must distinguish your cell from all others in the
633 AFS global namespace. By convention, the cell name is the second
634 element in any AFS pathname; therefore, a unique cell name guarantees
635 that every AFS pathname uniquely identifies a file, even if cells use
636 the same directory names at lower levels in their local AFS
637 filespace. For example, both the Example Corporation cell and the Example
638 Organization cell can have a home directory for the user <emphasis
639 role="bold">pat</emphasis>, because the pathnames are distinct:
640 <emphasis role="bold">/afs/example.com/usr/pat</emphasis> and <emphasis
641 role="bold">/afs/example.org/usr/pat</emphasis>.</para>
643 <para>By convention, cell names follow the Domain Name System (DNS)
644 conventions for domain names. If you are already an Internet site,
645 then it is simplest and strongly recommended to choose your Internet
646 domain name as the cell name.</para>
648 <para>If you are not an Internet site, it is best to choose a unique
649 DNS-style name, particularly if you plan to connect to the Internet in
650 the future. There are a few constraints on AFS cell names:
653 <para>It can contain as many as 64 characters, but shorter names
654 are better because the cell name frequently is part of machine
655 and file names. If your cell name is long, you can reduce
656 pathname length either by creating a symbolic link to the
657 complete cell name, at the second level in your file tree or by
658 using the <emphasis role="bold">CellAlias</emphasis>
659 configuration file on a client machine. See <link
660 linkend="HDRWQ42">The Second (Cellname) Level</link>.</para>
664 <para>To guarantee it is suitable for different operating system
665 types, the cell name can contain only lowercase characters,
666 numbers, underscores, dashes, and periods. Do not include
667 command shell metacharacters.</para>
671 <para>It can include any number of fields, which are
672 conventionally separated by periods (see the examples
678 <sect2 id="Header_43">
679 <title>How to Set the Cell Name</title>
682 <primary>setting</primary>
683 <secondary>cell name</secondary>
687 <primary>cell</primary>
688 <secondary>name</secondary>
689 <tertiary>setting</tertiary>
693 <primary>server machine</primary>
694 <secondary>setting home cell</secondary>
698 <primary>client machine</primary>
699 <secondary>setting home cell</secondary>
702 <para>The cell name is recorded in two files on the local disk of
703 each file server and client machine. Among other functions, these
704 files define the machine's cell membership and so affect how
705 programs and processes run on the machine; see <link
706 linkend="HDRWQ35">Why Choosing the Appropriate Cell Name is
707 Important</link>. The procedure for setting the cell name is
708 different for the two types of machines.</para>
710 <para>For file server machines, the two files that record the cell
711 name are the <emphasis role="bold">/usr/afs/etc/ThisCell</emphasis>
712 and <emphasis role="bold">/usr/afs/etc/CellServDB</emphasis>
713 files. As described more explicitly in the <emphasis>OpenAFS Quick
714 Start Guide</emphasis>, you set the cell name in both by issuing the
715 <emphasis role="bold">bos setcellname</emphasis> command on the
716 first file server machine you install in your cell. It is not
717 usually necessary to issue the command again. If you use the Update
718 Server, it distributes its copy of the <emphasis
719 role="bold">ThisCell</emphasis> and <emphasis
720 role="bold">CellServDB</emphasis> files to additional server
721 machines that you install. If you do not use the Update Server, the
722 <emphasis>OpenAFS Quick Start Guide</emphasis> explains how to copy
723 the files manually.</para>
725 <para>For client machines, the two files that record the cell name
726 are the <emphasis role="bold">/usr/vice/etc/ThisCell</emphasis> and
727 <emphasis role="bold">/usr/vice/etc/CellServDB</emphasis> files. You
728 create these files on a per-client basis, either with a text editor
729 or by copying them onto the machine from a central source in AFS.
730 See <link linkend="HDRWQ406">Maintaining Knowledge of Database
731 Server Machines</link> for details.</para>
733 <para>Change the cell name in these files only when you want to
734 transfer the machine to a different cell (client machines can only
735 have one default cell at a time and server machines can only belong
736 to one cell at a time). If the machine is a file server, follow the
737 complete set of instructions in the <emphasis>OpenAFS Quick Start
738 Guide</emphasis> for configuring a new cell. If the machine is a
739 client, all you need to do is change the files appropriately and
740 reboot the machine. The next section explains further the negative
741 consequences of changing the name of an existing cell.</para>
743 <para>To set the default cell name used by most AFS commands without
744 changing the local <emphasis
745 role="bold">/usr/vice/etc/ThisCell</emphasis> file, set the AFSCELL
746 environment variable in the command shell. It is worth setting this
747 variable if you need to complete significant administrative work in
748 a foreign cell.</para>
751 <para>The <emphasis role="bold">fs checkservers</emphasis> and
752 <emphasis role="bold">fs mkmount</emphasis> commands do not use
753 the AFSCELL variable. The <emphasis role="bold">fs
754 checkservers</emphasis> command always defaults to the cell named
755 in the <emphasis role="bold">ThisCell</emphasis> file, unless the
756 <emphasis role="bold">-cell</emphasis> argument is used. The
757 <emphasis role="bold">fs mkmount</emphasis> command defaults to
758 the cell in which the parent directory of the new mount point
764 <title>Why Choosing the Appropriate Cell Name is Important</title>
767 <primary>ThisCell file (client)</primary>
768 <secondary>how used by programs</secondary>
771 <para>Take care to select a cell name that is suitable for long-term
772 use. Changing a cell name later is complicated. An appropriate cell
773 name is important because it is the second element in the pathname
774 of all files in a cell's file tree. Because each cell name is
775 unique, its presence in an AFS pathname makes the pathname unique in
776 the AFS global namespace, even if multiple cells use similar
777 filespace organization at lower levels. For instance, it means that
778 every cell can have a home directory called <emphasis
779 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
780 role="bold">/usr/pat</emphasis> without causing a conflict. The
781 presence of the cell name in pathnames also means that users in
782 every cell use the same pathname to access a file, whether the file
783 resides in their local cell or in a foreign cell.</para>
785 <para>Another reason to choose the correct cell name early in the
786 process of installing your cell is that the cell membership defined
787 in each machine's <emphasis role="bold">ThisCell</emphasis> file
788 affects the performance of many programs and processes running on
789 the machine. For instance, AFS commands (<emphasis
790 role="bold">fs</emphasis>, <emphasis role="bold">pts</emphasis>, and
791 <emphasis role="bold">vos</emphasis> commands, for example) by
792 default execute in the cell of the machine on which they are
793 issued. The command interpreters check the <emphasis
794 role="bold">ThisCell</emphasis> file on the local disk and then
795 contact the database server machines listed in the <emphasis
796 role="bold">CellServDB</emphasis> file or configured in DNS for the
797 indicated cell. (The <emphasis role="bold">bos</emphasis> commands
798 work differently because the issuer always has to name of the
799 machine on which to run the command.)</para>
801 <para>The <emphasis role="bold">ThisCell</emphasis> file also
802 normally determines the cell for which a user receives an AFS token
803 when he or she logs in to a machine.</para>
805 <para>If you change the cell name, you must change the <emphasis
806 role="bold">ThisCell</emphasis> and <emphasis
807 role="bold">CellServDB</emphasis> files on every server and client
808 machine. Failure to change them all will cause many commands from
809 the AFS suites to not work as expected.</para>
814 <title>Participating in the AFS Global Namespace</title>
817 <primary>participation</primary>
818 <secondary>in AFS global namespace</secondary>
822 <primary>AFS</primary>
823 <secondary>global namespace</secondary>
827 <primary>global namespace</primary>
830 <para>Participating in the AFS global namespace makes your cell's
831 local file tree visible to AFS users in foreign cells and makes other
832 cells' file trees visible to your local users. It makes file sharing
833 across cells just as easy as sharing within a cell. This section
834 outlines the procedures necessary for participating in the global
838 <para>Participation in the global namespace is not
839 mandatory. Some cells use AFS primarily to facilitate file
840 sharing within the cell, and are not interested in providing
841 their users with access to foreign cells.</para>
845 <para>Making your file tree visible does not mean making it
846 vulnerable. You control how foreign users access your cell using
847 the same protection mechanisms that control local users'
848 access. See <link linkend="HDRWQ40">Granting and Denying Foreign
849 Users Access to Your Cell</link>.</para>
853 <para>The two aspects of participation are independent. A cell
854 can make its file tree visible without allowing its users to see
855 foreign cells' file trees, or can enable its users to see other
856 file trees without advertising its own.</para>
860 <para>You make your cell visible to others by advertising your
861 database server machines and allowing users at other sites to
862 access your database server and file server machines. See <link
863 linkend="HDRWQ38">Making Your Cell Visible to
864 Others</link>.</para>
868 <para>You control access to foreign cells on a per-client
869 machine basis. In other words, it is possible to make a foreign
870 cell accessible from one client machine in your cell but not
871 another. See <link linkend="HDRWQ39">Making Other Cells Visible
872 in Your Cell</link>.</para>
878 <title>What the Global Namespace Looks Like</title>
881 <primary>conventions</primary>
882 <secondary>AFS pathnames</secondary>
886 <primary>AFS</primary>
887 <secondary>root directory (/afs)</secondary>
888 <tertiary>on client machine</tertiary>
892 <primary>directories</primary>
893 <secondary>/afs</secondary>
897 <primary>directories</primary>
898 <secondary>/afs/<emphasis>cellname</emphasis></secondary>
902 <primary>cell</primary>
903 <secondary>name</secondary>
904 <tertiary>at second level in file tree</tertiary>
907 <para>The AFS global namespace appears the same to all AFS cells
908 that participate in it, because they all agree to follow a small set
909 of conventions in constructing pathnames.</para>
911 <para>The first convention is that all AFS pathnames begin with the
912 string <emphasis role="bold">/afs</emphasis> to indicate that they
913 belong to the AFS global namespace.</para>
915 <para>The second convention is that the cell name is the second
916 element in an AFS pathname; it indicates where the file resides
917 (that is, the cell in which a file server machine houses the
918 file). As noted, the presence of a cell name in pathnames makes the
919 global namespace possible, because it guarantees that all AFS
920 pathnames are unique even if cells use the same directory names at
921 lower levels in their AFS filespace.</para>
923 <para>What appears at the third and lower levels in an AFS pathname
924 depends on how a cell has chosen to arrange its filespace. There
925 are some suggested conventional directories at the third level; see
926 <link linkend="HDRWQ43">The Third Level</link>.</para>
930 <title>Making Your Cell Visible to Others</title>
933 <primary>cell</primary>
934 <secondary>making local visible to foreign</secondary>
938 <primary>local cell</primary>
939 <secondary>making visible to foreign cells</secondary>
943 <primary>foreign cell</primary>
944 <secondary>making local cell visible</secondary>
947 <para>You make your cell visible to others by advertising your cell
948 name and database server machines. Just like client machines in the
949 local cell, the Cache Manager on machines in foreign cells use the
950 information to reach your cell's Volume Location (VL) Servers when
951 they need volume and file location information. For authenticated
952 access, foreign clients must be configured with the necessary
953 Kerberos version 5 domain-to-realm mappings and Key Distribution
954 Center (KDC) location information for both the local and remote
955 Kerberos version 5 realms.</para>
957 <para>There are two places you can make this information available:
960 <primary>files</primary>
962 <secondary>global CellServDB</secondary>
966 <primary>CellServDB file maintained by the AFS
969 <secondary>as global update source</secondary>
973 <para>In the global <emphasis
974 role="bold">CellServDB</emphasis> file maintained by the AFS
975 Registrar. This file lists the name and database server
976 machines of every cell that has agreed to make this
977 information available to other cells. This file is available
979 url="http://grand.central.org/csdb.html">http://grand.central.org/csdb.html</ulink></para>
981 <para>To add or change your cell's listing in this file,
982 follow the instructions at <ulink
983 url="http://grand.central.org/csdb.html">http://grand.central.org/csdb.html</ulink>.
984 It is a good policy to check the file for changes on a
985 regular schedule. An updated copy of this file is included
986 with new releases of OpenAFS.</para>
989 <primary>files</primary>
991 <secondary>CellServDB.local</secondary>
995 <primary>CellServDB.local file</primary>
1000 <para>A file called <emphasis
1001 role="bold">CellServDB.local</emphasis> in the <emphasis
1002 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1003 role="bold">/service/etc</emphasis> directory of your cell's
1004 filespace. List only your cell's database server
1010 <para>Update the files whenever you change the identity of your
1011 cell's database server machines. Also update the copies of the
1012 <emphasis role="bold">CellServDB</emphasis> files on all of your
1013 server machines (in the <emphasis
1014 role="bold">/usr/afs/etc</emphasis> directory) and client machines
1015 (in the <emphasis role="bold">/usr/vice/etc</emphasis>
1016 directory). For instructions, see <link
1017 linkend="HDRWQ118">Maintaining the Server CellServDB File</link> and
1018 <link linkend="HDRWQ406">Maintaining Knowledge of Database Server
1019 Machines</link>.</para>
1021 <para>Once you have advertised your database server machines, it can
1022 be difficult to make your cell invisible again. You can remove the
1023 <emphasis role="bold">CellServDB.local</emphasis> file and ask the
1024 AFS Registrar to remove your entry from the global <emphasis
1025 role="bold">CellServDB</emphasis> file, but other cells probably
1026 have an entry for your cell in their local <emphasis
1027 role="bold">CellServDB</emphasis> files already. To make those
1028 entries invalid, you must change the names or IP addresses of your
1029 database server machines.</para>
1031 <para>Your cell does not have to be invisible to be inaccessible,
1032 however. To make your cell completely inaccessible to foreign users,
1033 remove the <emphasis role="bold">system:anyuser</emphasis> group
1034 from all ACLs at the top three levels of your filespace; see <link
1035 linkend="HDRWQ40">Granting and Denying Foreign Users Access to Your
1039 <primary>cell</primary>
1041 <secondary>making foreign visible to local</secondary>
1045 <primary>local cell</primary>
1047 <secondary>making foreign cells visible in</secondary>
1051 <primary>foreign cell</primary>
1053 <secondary>making visible in local cell</secondary>
1057 <primary>client machine</primary>
1059 <secondary>making foreign cell visible</secondary>
1063 <sect2 id="HDRWQ39">
1064 <title>Making Other Cells Visible in Your Cell</title>
1066 <para>To make a foreign cell's filespace visible on a client machine
1067 in your cell that is not configured for <emphasis
1068 role="bold">Freelance Mode</emphasis> or <emphasis
1069 role="bold">Dynamic Root</emphasis> mode, perform the following
1073 <para>Mount the cell's <emphasis
1074 role="bold">root.cell</emphasis> volume at the second level in
1075 your cell's filespace just below the <emphasis
1076 role="bold">/afs</emphasis> directory. Use the <emphasis
1077 role="bold">fs mkmount</emphasis> command with the <emphasis
1078 role="bold">-cell</emphasis> argument as instructed in <link
1079 linkend="HDRWQ213">To create a cellular mount
1080 point</link>.</para>
1084 <para>Mount AFS at the <emphasis role="bold">/afs</emphasis>
1085 directory on the client machine. The <emphasis
1086 role="bold">afsd</emphasis> program, which initializes the
1087 Cache Manager, performs the mount automatically at the
1088 directory named in the first field of the local <emphasis
1089 role="bold">/usr/vice/etc/cacheinfo</emphasis> file or by the
1090 command's <emphasis role="bold">-mountdir</emphasis>
1091 argument. Mounting AFS at an alternate location makes it
1092 impossible to reach the filespace of any cell that mounts its
1093 <emphasis role="bold">root.afs</emphasis> and <emphasis
1094 role="bold">root.cell</emphasis> volumes at the conventional
1095 locations. See <link linkend="HDRWQ395">Displaying and Setting
1096 the Cache Size and Location</link>.</para>
1100 <para>Create an entry for the cell in the list of database
1101 server machines which the Cache Manager maintains in kernel
1105 role="bold">/usr/vice/etc/CellServDB</emphasis> file on every
1106 client machine's local disk lists the database server machines
1107 for the local and foreign cells. The <emphasis
1108 role="bold">afsd</emphasis> program reads the contents of the
1109 <emphasis role="bold">CellServDB</emphasis> file into kernel
1110 memory as it initializes the Cache Manager. You can also use
1111 the <emphasis role="bold">fs newcell</emphasis> command to add
1112 or alter entries in kernel memory directly between reboots of
1113 the machine. See <link linkend="HDRWQ406">Maintaining
1114 Knowledge of Database Server Machines</link>.</para>
1119 <para>Non-windows client machines may enable <emphasis
1120 role="bold">Dynamic Root Mode</emphasis> by using the <emphasis
1121 role="bold">-dynroot</emphasis> option to <emphasis
1122 role="bold">afsd</emphasis>. When this option is enabled, all cells
1123 listed in the <emphasis role="bold">CellServDB</emphasis> file will
1124 appear in the <emphasis role="bold">/afs</emphasis> directory. The
1125 contents of the <emphasis role="bold">root.afs</emphasis> volume
1126 will be ignored. </para>
1128 <para>Windows client machines may enable <emphasis
1129 role="bold">Freelance Mode</emphasis> during client installation or
1130 by setting the <emphasis role="bold">FreelanceClient</emphasis>
1131 setting under <emphasis role="bold">Service Parameters</emphasis> in
1132 the Windows Registry as mentioned in the <ulink
1133 url="http://docs.openafs.org/ReleaseNotesWindows/">Release
1134 Notes</ulink>. When this option is enabled, the <emphasis
1135 role="bold">root.afs</emphasis> volume is ignored and a mounpoint
1136 for each cell is automatically created in the the <emphasis
1137 role="bold">\\AFS</emphasis> directory when the folder <emphasis
1138 role="bold">\\AFS\<replaceable>cellname</replaceable></emphasis> is
1139 accessed and the foreign Volume Location servers can be reached.
1140 </para> <para>Note that making a foreign cell visible to client
1141 machines does not guarantee that your users can access its
1142 filespace. The ACLs in the foreign cell must also grant them the
1143 necessary permissions.</para>
1146 <primary>cell</primary>
1148 <secondary>granting local access to foreign users</secondary>
1152 <primary>local cell</primary>
1154 <secondary>granting foreign users access to</secondary>
1158 <sect2 id="HDRWQ40">
1159 <title>Granting and Denying Foreign Users Access to Your
1162 <para>Making your cell visible in the AFS global namespace does not
1163 take away your control over the way in which users from foreign
1164 cells access your file tree.</para>
1166 <para>By default, foreign users access your cell as the user
1167 <emphasis role="bold">anonymous</emphasis>, which means they have
1168 only the permissions granted to the <emphasis
1169 role="bold">system:anyuser</emphasis> group on each directory's
1170 ACL. Normally these permissions are limited to the <emphasis
1171 role="bold">l</emphasis> (<emphasis role="bold">lookup</emphasis>)
1172 and <emphasis role="bold">r</emphasis> (<emphasis
1173 role="bold">read</emphasis>) permissions.</para>
1175 <para>There are three ways to grant wider access to foreign users:
1178 <para>Grant additional permissions to the <emphasis
1179 role="bold">system:anyuser</emphasis> group on certain
1180 ACLs. Keep in mind, however, that all users can then access
1181 that directory in the indicated way (not just specific foreign
1182 users you have in mind).</para>
1186 <para>Enable automatic registration for users in the foreign
1187 cell. This may be done by creating a cross-realm trust in the
1188 <emphasis role="bold">Kerberos Database</emphasis>. Then add a
1189 PTS group named <emphasis
1190 role="bold">system:authuser<replaceable>@FOREIGN.REALM</replaceable></emphasis>
1191 and give it a group quota greater than the number of foreign
1192 users expected to be registered. After the cross-realm trust
1193 and the PTS group are created, the <ulink
1194 url="http://docs.openafs.org/Reference/1/aklog.html">aklog</ulink>
1195 command will automatically register foreign users as
1196 needed. Consult the documentation for your <emphasis
1197 role="bold">Kerberos Server</emphasis> for instructions on how
1198 to establish a cross-realm trust. </para>
1202 <para>Create a local authentication account for specific
1203 foreign users, by creating entries in the Protection Database,
1204 the Kerberos Database, and the local password file.</para>
1210 <primary>cell</primary>
1212 <secondary>filespace configuration issues</secondary>
1216 <primary>configuring</primary>
1218 <secondary>filespace, issues</secondary>
1222 <primary>file tree</primary>
1224 <secondary>conventions</secondary>
1226 <tertiary>for configuring</tertiary>
1231 <sect1 id="HDRWQ41">
1232 <title>Configuring Your AFS Filespace</title>
1234 <para>This section summarizes the issues to consider when configuring
1235 your AFS filespace. For a discussion of creating volumes that
1236 correspond most efficiently to the filespace's directory structure,
1237 see <link linkend="HDRWQ44">Creating Volumes to Simplify
1238 Administration</link>.</para>
1241 <para><emphasis role="bold">For Windows users:</emphasis> Windows
1242 uses a backslash (<emphasis role="bold">\</emphasis>) rather than a
1243 forward slash (<emphasis role="bold">/</emphasis>) to separate the
1244 elements in a pathname. The hierarchical organization of the
1245 filespace is however the same as on a UNIX machine.</para>
1248 <para>AFS pathnames must follow a few conventions so the AFS global
1249 namespace looks the same from any AFS client machine. There are
1250 corresponding conventions to follow in building your file tree, not
1251 just because pathnames reflect the structure of a file tree, but also
1252 because the AFS Cache Manager expects a certain configuration.</para>
1255 <primary>AFS</primary>
1257 <secondary>root directory (/afs)</secondary>
1259 <tertiary>in cell filespace</tertiary>
1263 <primary>directories</primary>
1265 <secondary>/afs</secondary>
1268 <sect2 id="Header_51">
1269 <title>The Top /afs Level</title>
1271 <para>The first convention is that the top level in your file tree
1272 be called the <emphasis role="bold">/afs</emphasis> directory. If
1273 you name it something else, then you must use the <emphasis
1274 role="bold">-mountdir</emphasis> argument with the <emphasis
1275 role="bold">afsd</emphasis> program to get Cache Managers to mount
1276 AFS properly. You cannot participate in the AFS global namespace in
1280 <primary>cell</primary>
1282 <secondary>name</secondary>
1284 <tertiary>at second level in file tree</tertiary>
1288 <primary>directories</primary>
1290 <secondary>/afs/<emphasis>cellname</emphasis></secondary>
1294 <primary>symbolic link</primary>
1296 <secondary>at second level of AFS pathname</secondary>
1300 <sect2 id="HDRWQ42">
1301 <title>The Second (Cellname) Level</title>
1303 <para>The second convention is that just below the <emphasis
1304 role="bold">/afs</emphasis> directory you place directories
1305 corresponding to each cell whose file tree is visible and accessible
1306 from the local cell. Minimally, there must be a directory for the
1307 local cell. Each such directory is a mount point to the indicated
1308 cell's <emphasis role="bold">root.cell</emphasis> volume. For
1309 example, in the Example Corporation cell, <emphasis
1310 role="bold">/afs/example.com</emphasis> is a mount point for the cell's
1311 own <emphasis role="bold">root.cell</emphasis> volume and <emphasis
1312 role="bold">example.org</emphasis> is a mount point for the Example
1313 Organization cell's <emphasis role="bold">root.cell</emphasis>
1314 volume. The <emphasis role="bold">fs lsmount</emphasis> command
1315 displays the mount points.</para>
1318 % <emphasis role="bold">fs lsmount /afs/example.com</emphasis>
1319 '/afs/example.com' is a mount point for volume '#root.cell'
1320 % <emphasis role="bold">fs lsmount /afs/example.org</emphasis>
1321 '/afs/example.org' is a mount point for volume '#example.org:root.cell'
1324 <para>To reduce the amount of typing necessary in pathnames, you can
1325 create a symbolic link with an abbreviated name to the mount point
1326 of each cell your users frequently access (particularly the home
1327 cell). In the Example Corporation cell, for instance, <emphasis
1328 role="bold">/afs/example</emphasis> is a symbolic link to the <emphasis
1329 role="bold">/afs/example.com</emphasis> mount point, as the <emphasis
1330 role="bold">fs lsmount</emphasis> command reveals.</para>
1333 % <emphasis role="bold">fs lsmount /afs/example</emphasis>
1334 '/afs/example' is a symbolic link, leading to a mount point for volume
1335 '#root.cell' </programlisting>
1338 <primary>file tree</primary>
1340 <secondary>conventions</secondary>
1342 <tertiary>third level</tertiary>
1346 <primary>directories</primary>
1348 <secondary>conventional under /afs/cellname</secondary>
1352 <sect2 id="HDRWQ43">
1353 <title>The Third Level</title>
1355 <para>You can organize the third level of your cell's file tree any
1356 way you wish. The following list describes directories that appear
1357 at this level in the conventional configuration:
1360 <term><emphasis role="bold">common</emphasis></term>
1363 <para>This directory contains programs and files needed by
1364 users working on machines of all system types, such as text
1365 editors, online documentation files, and so on. Its
1366 <emphasis role="bold">/etc</emphasis> subdirectory is a
1367 logical place to keep the central update sources for files
1368 used on all of your cell's client machines, such as the
1369 <emphasis role="bold">ThisCell</emphasis> and <emphasis
1370 role="bold">CellServDB</emphasis> files.</para>
1375 <term><emphasis role="bold">public</emphasis></term>
1378 <para>A directory accessible to anyone who can access your
1379 filespace, because its ACL grants the <emphasis
1380 role="bold">l</emphasis> (<emphasis
1381 role="bold">lookup</emphasis>) and <emphasis
1382 role="bold">r</emphasis> (<emphasis
1383 role="bold">read</emphasis>) permissions to the <emphasis
1384 role="bold">system:anyuser</emphasis> group. It is useful if
1385 you want to enable your users to make selected information
1386 available to everyone, but do not want to grant foreign
1387 users access to the contents of the <emphasis
1388 role="bold">usr</emphasis> directory which houses user home
1389 directories (and is also at this level). It is conventional
1390 to create a subdirectory for each of your cell's
1396 <term><emphasis role="bold">service</emphasis></term>
1399 <para>This directory contains files and subdirectories that
1400 help cells coordinate resource sharing. For a list of the
1401 proposed standard files and subdirectories to create, call
1402 or write to AFS Product Support.</para>
1404 <para>As an example, files that other cells expect to find
1405 in this directory's <emphasis role="bold">etc</emphasis>
1406 subdirectory can include the following: <itemizedlist>
1409 role="bold">CellServDB.export</emphasis>, a list of
1410 database server machines for many cells</para>
1415 role="bold">CellServDB.local</emphasis>, a list of the
1416 cell's own database server machines</para>
1420 <para><emphasis role="bold">passwd</emphasis>, a copy
1421 of the local password file (<emphasis
1422 role="bold">/etc/passwd</emphasis> or equivalent) kept
1423 on the local disk of the cell's client machines</para>
1427 <para><emphasis role="bold">group</emphasis>, a copy
1428 of the local groups file (<emphasis
1429 role="bold">/etc/group</emphasis> or equivalent) kept
1430 on the local disk of the cell's client machines</para>
1438 <term><emphasis>sys_type</emphasis></term>
1441 <para>A separate directory for storing the server and client
1442 binaries for each system type you use in the cell.
1443 Configuration is simplest if you use the system type names
1444 assigned in the AFS distribution, particularly if you wish
1445 to use the <emphasis role="bold">@sys</emphasis> variable in
1446 pathnames (see <link linkend="HDRWQ56">Using the @sys
1447 Variable in Pathnames</link>). The <emphasis>OpenAFS Release
1448 Notes</emphasis> lists the conventional name for each
1449 supported system type.</para>
1451 <para>Within each such directory, create directories named
1452 <emphasis role="bold">bin</emphasis>, <emphasis
1453 role="bold">etc</emphasis>, <emphasis
1454 role="bold">usr</emphasis>, and so on, to store the programs
1455 normally kept in the <emphasis role="bold">/bin</emphasis>,
1456 <emphasis role="bold">/etc</emphasis> and <emphasis
1457 role="bold">/usr</emphasis> directories on a local
1458 disk. Then create symbolic links from the local directories
1459 on client machines into AFS; see <link
1460 linkend="HDRWQ55">Configuring the Local Disk</link>. Even if
1461 you do not choose to use symbolic links in this way, it can
1462 be convenient to have central copies of system binaries in
1463 AFS. If binaries are accidentally removed from a machine,
1464 you can recopy them onto the local disk from AFS rather than
1465 having to recover them from tape</para>
1470 <term><emphasis role="bold">usr</emphasis></term>
1473 <para>This directory contains home directories for your
1474 local users. As discussed in the previous entry for the
1475 <emphasis role="bold">public</emphasis> directory, it is
1476 often practical to protect this directory so that only
1477 locally authenticated users can access it. This keeps the
1478 contents of your user's home directories as secure as
1481 <para>If your cell is quite large, directory lookup can be
1482 slowed if you put all home directories in a single <emphasis
1483 role="bold">usr</emphasis> directory. For suggestions on
1484 distributing user home directories among multiple grouping
1485 directories, see <link linkend="HDRWQ59">Grouping Home
1486 Directories</link>.</para>
1487 </listitem> </varlistentry>
1493 <primary>volume name</primary>
1495 <secondary>conventions for</secondary>
1499 <primary>conventions</primary>
1501 <secondary>volume names</secondary>
1505 <primary>volume</primary>
1507 <secondary>separate for each top level directory</secondary>
1511 <primary>file tree</primary>
1513 <secondary>creating volumes to match top level
1514 directories</secondary>
1519 <sect1 id="HDRWQ44">
1520 <title>Creating Volumes to Simplify Administration</title>
1522 <para>This section discusses how to create volumes in ways that make
1523 administering your system easier.</para>
1525 <para>At the top levels of your file tree (at least through the third
1526 level), each directory generally corresponds to a separate
1527 volume. Some cells also configure the subdirectories of some third
1528 level directories as separate volumes. Common examples are the
1530 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1531 role="bold">/common</emphasis> and <emphasis
1532 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1533 role="bold">/usr</emphasis> directories.</para>
1535 <para>You do not have to create a separate volume for every directory
1536 level in a tree, but the advantage is that each volume tends to be
1537 smaller and easier to move for load balancing. The overhead for a
1538 mount point is no greater than for a standard directory, nor does the
1539 volume structure itself require much disk space. Most cells find that
1540 below the fourth level in the tree, using a separate volume for each
1541 directory is no longer efficient. For instance, while each user's home
1542 directory (at the fourth level in the tree) corresponds to a separate
1543 volume, all of the subdirectories in the home directory normally
1544 reside in the same volume.</para>
1546 <para>Keep in mind that only one volume can be mounted at a given
1547 directory location in the tree. In contrast, a volume can be mounted
1548 at several locations, though this is not recommended because it
1549 distorts the hierarchical nature of the file tree, potentially causing
1553 <primary>volume name</primary>
1555 <secondary>restrictions</secondary>
1559 <primary>restrictions</primary>
1561 <secondary>on volume names</secondary>
1565 <primary>volume name</primary>
1567 <secondary>two required</secondary>
1571 <primary>volume</primary>
1573 <secondary>root (root.afs and root.cell)</secondary>
1577 <primary>root volumes (root.afs and root.cell)</primary>
1580 <sect2 id="Header_55">
1581 <title>Assigning Volume Names</title>
1583 <para>You can name your volumes anything you choose, subject to a
1587 <para>Read/write volume names can be up to 22 characters in
1588 length. The maximum length for volume names is 31 characters,
1589 and there must be room to add the <emphasis
1590 role="bold">.readonly</emphasis> extension on read-only
1595 <para>Do not add the <emphasis
1596 role="bold">.readonly</emphasis> and <emphasis
1597 role="bold">.backup</emphasis> extensions to volume names
1598 yourself, even if they are appropriate. The Volume Server adds
1599 them automatically as it creates a read-only or backup version
1604 <para>There must be volumes named <emphasis
1605 role="bold">root.afs</emphasis> and <emphasis
1606 role="bold">root.cell</emphasis>, mounted respectively at the
1607 top (<emphasis role="bold">/afs</emphasis>) level in the
1608 filespace and just below that level, at the cell's name (for
1609 example, at <emphasis role="bold">/afs/example.com</emphasis> in
1610 the Example Corporation cell).</para>
1612 <para>Deviating from these names only creates confusion and
1613 extra work. Changing the name of the <emphasis
1614 role="bold">root.afs</emphasis> volume, for instance, means
1615 that you must use the <emphasis
1616 role="bold">-rootvol</emphasis> argument to the <emphasis
1617 role="bold">afsd</emphasis> program on every client machine,
1618 to name the alternate volume.</para>
1620 <para>Similarly, changing the <emphasis
1621 role="bold">root.cell</emphasis> volume name prevents users in
1622 foreign cells from accessing your filespace, if the mount
1623 point for your cell in their filespace refers to the
1624 conventional <emphasis role="bold">root.cell</emphasis>
1625 name. Of course, this is one way to make your cell invisible
1626 to other cells.</para>
1631 <para>It is best to assign volume names that indicate the type of
1632 data they contain, and to use similar names for volumes with similar
1633 contents. It is also helpful if the volume name is similar to (or at
1634 least has elements in common with) the name of the directory at
1635 which it is mounted. Understanding the pattern then enables you
1636 accurately to guess what a volume contains and where it is
1639 <para>Many cells find that the most effective volume naming scheme
1640 puts a common prefix on the names of all related volumes. <link
1641 linkend="TBLVOL-PREFIX">Table 1</link> describes the recommended
1642 prefixing scheme.</para>
1644 <table id="TBLVOL-PREFIX" label="1">
1645 <title>Suggested volume prefixes</title>
1648 <colspec colwidth="14*" />
1650 <colspec colwidth="28*" />
1652 <colspec colwidth="22*" />
1654 <colspec colwidth="36*" />
1658 <entry><emphasis role="bold">Prefix</emphasis></entry>
1660 <entry><emphasis role="bold">Contents</emphasis></entry>
1662 <entry><emphasis role="bold">Example Name</emphasis></entry>
1664 <entry><emphasis role="bold">Example Mount
1665 Point</emphasis></entry>
1671 <entry><emphasis role="bold">common.</emphasis></entry>
1673 <entry>popular programs and files</entry>
1675 <entry><emphasis role="bold">common.etc</emphasis></entry>
1678 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1679 role="bold">/common/etc</emphasis></entry>
1683 <entry><emphasis role="bold">src.</emphasis></entry>
1685 <entry>source code</entry>
1687 <entry><emphasis role="bold">src.afs</emphasis></entry>
1690 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1691 role="bold">/src/afs</emphasis></entry>
1695 <entry><emphasis role="bold">proj.</emphasis></entry>
1697 <entry>project data</entry>
1699 <entry><emphasis role="bold">proj.portafs</emphasis></entry>
1702 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1703 role="bold">/proj/portafs</emphasis></entry>
1707 <entry><emphasis role="bold">test.</emphasis></entry>
1709 <entry>testing or other temporary data</entry>
1711 <entry><emphasis role="bold">test.smith</emphasis></entry>
1714 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1715 role="bold">/usr/smith/test</emphasis></entry>
1719 <entry><emphasis role="bold">user.</emphasis></entry>
1721 <entry>user home directory data</entry>
1723 <entry><emphasis role="bold">user.terry</emphasis></entry>
1726 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1727 role="bold">/usr/terry</emphasis></entry>
1731 <entry>sys_type<emphasis role="bold">.</emphasis></entry>
1733 <entry>programs compiled for an operating system
1736 <entry><emphasis role="bold">rs_aix42.bin</emphasis></entry>
1739 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1740 role="bold">/rs_aix42/bin</emphasis></entry>
1746 <para><link linkend="TBLPREFIX-EXAMPLE">Table 2</link> is a more
1747 specific example for a cell's <emphasis
1748 role="bold">rs_aix42</emphasis> system volumes and
1751 <table id="TBLPREFIX-EXAMPLE" label="2">
1752 <title>Example volume-prefixing scheme</title>
1755 <colspec colwidth="14*" />
1757 <colspec colwidth="28*" />
1759 <colspec colwidth="22*" />
1761 <colspec colwidth="36*" />
1765 <entry><emphasis role="bold">Example Name</emphasis></entry>
1767 <entry><emphasis role="bold">Example Mount
1768 Point</emphasis></entry>
1774 <entry><emphasis role="bold">rs_aix42.bin</emphasis></entry>
1777 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1778 role="bold">/rs_aix42/bin</emphasis>, <emphasis
1779 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1780 role="bold">/rs_aix42/bin</emphasis></entry>
1784 <entry><emphasis role="bold">rs_aix42.etc</emphasis></entry>
1787 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1788 role="bold">/rs_aix42/etc</emphasis></entry>
1792 <entry><emphasis role="bold">rs_aix42.usr</emphasis></entry>
1795 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1796 role="bold">/rs_aix42/usr</emphasis></entry>
1801 role="bold">rs_aix42.usr.afsws</emphasis></entry>
1804 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1805 role="bold">/rs_aix42/usr/afsws</emphasis></entry>
1810 role="bold">rs_aix42.usr.lib</emphasis></entry>
1813 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1814 role="bold">/rs_aix42/usr/lib</emphasis></entry>
1819 role="bold">rs_aix42.usr.bin</emphasis></entry>
1822 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1823 role="bold">/rs_aix42/usr/bin</emphasis></entry>
1828 role="bold">rs_aix42.usr.etc</emphasis></entry>
1831 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1832 role="bold">/rs_aix42/usr/etc</emphasis></entry>
1837 role="bold">rs_aix42.usr.inc</emphasis></entry>
1840 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1841 role="bold">/rs_aix42/usr/inc</emphasis></entry>
1846 role="bold">rs_aix42.usr.man</emphasis></entry>
1849 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1850 role="bold">/rs_aix42/usr/man</emphasis></entry>
1855 role="bold">rs_aix42.usr.sys</emphasis></entry>
1858 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1859 role="bold">/rs_aix42/usr/sys</emphasis></entry>
1864 role="bold">rs_aix42.usr.local</emphasis></entry>
1867 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
1868 role="bold">/rs_aix42/usr/local</emphasis></entry>
1874 <para>There are several advantages to this scheme:
1877 <para>The volume name is similar to the mount point name in
1878 the filespace. In all of the entries in <link
1879 linkend="TBLPREFIX-EXAMPLE">Table 2</link>, for example, the
1880 only difference between the volume and mount point name is
1881 that the former uses periods as separators and the latter uses
1882 slashes. Another advantage is that the volume name indicates
1883 the contents, or at least suggests the directory on which to
1884 issue the <emphasis role="bold">ls</emphasis> command to learn
1885 the contents.</para>
1889 <para>It makes it easy to manipulate groups of related volumes
1890 at one time. In particular, the <emphasis role="bold">vos
1891 backupsys</emphasis> command's <emphasis
1892 role="bold">-prefix</emphasis> argument enables you to create
1893 a backup version of every volume whose name starts with the
1894 same string of characters. Making a backup version of each
1895 volume is one of the first steps in backing up a volume with
1896 the AFS Backup System, and doing it for many volumes with one
1897 command saves you a good deal of typing. For instructions for
1898 creating backup volumes, see <link linkend="HDRWQ201">Creating
1899 Backup Volumes</link>, For information on the AFS Backup
1900 System, see <link linkend="HDRWQ248">Configuring the AFS
1901 Backup System</link> and <link linkend="HDRWQ283">Backing Up
1902 and Restoring AFS Data</link>.</para>
1906 <para>It makes it easy to group related volumes together on a
1907 partition. Grouping related volumes together has several
1908 advantages of its own, discussed in <link
1909 linkend="HDRWQ49">Grouping Related Volumes on a
1910 Partition</link>.</para>
1916 <primary>volume</primary>
1918 <secondary>grouping related on same partition</secondary>
1922 <primary>disk partition</primary>
1924 <secondary>grouping related volumes on</secondary>
1928 <sect2 id="HDRWQ49">
1929 <title>Grouping Related Volumes on a Partition</title>
1931 <para>If your cell is large enough to make it practical, consider
1932 grouping related volumes together on a partition. In general, you
1933 need at least three file server machines for volume grouping to be
1934 effective. Grouping has several advantages, which are most obvious
1935 when the file server machine becomes inaccessible:
1938 <para>If you keep a hardcopy record of the volumes on a
1939 partition, you know which volumes are unavailable. You can
1940 keep such a record without grouping related volumes, but a
1941 list composed of unrelated volumes is much harder to maintain.
1942 Note that the record must be on paper, because the outage can
1943 prevent you from accessing an online copy or from issuing the
1944 <emphasis role="bold">vos listvol</emphasis> command, which
1945 gives you the same information.</para>
1949 <para>The effect of an outage is more localized. For example,
1950 if all of the binaries for a given system type are on one
1951 partition, then only users of that system type are
1952 affected. If a partition houses binary volumes from several
1953 system types, then an outage can affect more people,
1954 particularly if the binaries that remain available are
1955 interdependent with those that are not available.</para>
1960 <para>The advantages of grouping related volumes on a partition do
1961 not necessarily extend to the grouping of all related volumes on one
1962 file server machine. For instance, it is probably unwise in a cell
1963 with two file server machines to put all system volumes on one
1964 machine and all user volumes on the other. An outage of either
1965 machine probably affects everyone.</para>
1967 <para>Admittedly, the need to move volumes for load balancing
1968 purposes can limit the practicality of grouping related volumes.
1969 You need to weigh the complementary advantages case by case.</para>
1972 <primary>replication</primary>
1974 <secondary>appropriate volumes</secondary>
1978 <primary>volume</primary>
1980 <secondary>type to replicate</secondary>
1984 <primary>volume</primary>
1986 <secondary>where to place replicated</secondary>
1990 <primary>read-only volume</primary>
1992 <secondary>selecting site</secondary>
1996 <sect2 id="HDRWQ50">
1997 <title>When to Replicate Volumes</title>
1999 <para>As discussed in <link linkend="HDRWQ15">Replication</link>,
2000 replication refers to making a copy, or clone, of a read/write
2001 source volume and then placing the copy on one or more additional
2002 file server machines. Replicating a volume can increase the
2003 availability of the contents. If one file server machine housing the
2004 volume becomes inaccessible, users can still access the copy of the
2005 volume stored on a different machine. No one machine is likely to
2006 become overburdened with requests for a popular file, either,
2007 because the file is available from several machines.</para>
2009 <para>However, replication is not appropriate for all cells. If a
2010 cell does not have much disk space, replication can be unduly
2011 expensive, because each clone not on the same partition as the
2012 read/write source takes up as much disk space as its source volume
2013 did at the time the clone was made. Also, if you have only one file
2014 server machine, replication uses up disk space without increasing
2015 availability.</para>
2017 <para>Replication is also not appropriate for volumes that change
2018 frequently. You must issue the <emphasis role="bold">vos
2019 release</emphasis> command every time you need to update a read-only
2020 volume to reflect changes in its read/write source.</para>
2022 <para>For both of these reasons, replication is appropriate only for
2023 popular volumes whose contents do not change very often, such as
2024 system binaries and other volumes mounted at the upper levels of
2025 your filespace. User volumes usually exist only in a read/write
2026 version since they change so often.</para>
2028 <para>If you are replicating any volumes, you must replicate the
2029 <emphasis role="bold">root.afs</emphasis> and <emphasis
2030 role="bold">root.cell</emphasis> volumes, preferably at two or three
2031 sites each (even if your cell only has two or three file server
2032 machines). The Cache Manager needs to pass through the directories
2033 corresponding to the <emphasis role="bold">root.afs</emphasis> and
2034 <emphasis role="bold">root.cell</emphasis> volumes as it interprets
2035 any pathname. The unavailability of these volumes makes all other
2036 volumes unavailable too, even if the file server machines storing
2037 the other volumes are still functioning.</para>
2039 <para>Another reason to replicate the <emphasis
2040 role="bold">root.afs</emphasis> volume is that it can lessen the
2041 load on the File Server machine. The Cache Manager has a bias to
2042 access a read-only version of the <emphasis
2043 role="bold">root.afs</emphasis> volume if it is replicate, which
2044 puts the Cache Manager onto the <emphasis>read-only path</emphasis>
2045 through the AFS filespace. While on the read-only path, the Cache
2046 Manager attempts to access a read-only copy of replicated
2047 volumes. The File Server needs to track only one callback per Cache
2048 Manager for all of the data in a read-only volume, rather than the
2049 one callback per file it must track for read/write volumes. Fewer
2050 callbacks translate into a smaller load on the File Server.</para>
2052 <para>If the <emphasis role="bold">root.afs</emphasis> volume is not
2053 replicated, the Cache Manager follows a read/write path through the
2054 filespace, accessing the read/write version of each volume. The File
2055 Server distributes and tracks a separate callback for each file in a
2056 read/write volume, imposing a greater load on it.</para>
2058 <para>For more on read/write and read-only paths, see <link
2059 linkend="HDRWQ209">The Rules of Mount Point Traversal</link>.</para>
2061 <para>It also makes sense to replicate system binary volumes in many
2062 cases, as well as the volume corresponding to the <emphasis
2063 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
2064 role="bold">/usr</emphasis> directory and the volumes corresponding
2066 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
2067 role="bold">/common</emphasis> directory and its
2068 subdirectories.</para>
2070 <para>It is a good idea to place a replica on the same partition as
2071 the read/write source. In this case, the read-only volume is a clone
2072 (like a backup volume): it is a copy of the source volume's vnode
2073 index, rather than a full copy of the volume contents. Only if the
2074 read/write volume moves to another partition or changes
2075 substantially does the read-only volume consume significant disk
2076 space. Read-only volumes kept on other servers' partitions always
2077 consume the full amount of disk space that the read/write source
2078 consumed when the read-only volume was created.</para>
2080 <para>You cannot have a replica volume on a different partition of
2081 the same server hosting the read/write volume. "Cheap" read-only
2082 volumes must be on the same partition as the read/write; all other
2083 read-only volumes must be on different servers.</para>
2086 <sect2 id="Header_58">
2087 <title>The Default Quota and ACL on a New Volume</title>
2089 <para>Every AFS volume has associated with it a quota that limits
2090 the amount of disk space the volume is allowed to use. To set and
2091 change quota, use the commands described in <link
2092 linkend="HDRWQ234">Setting and Displaying Volume Quota and Current
2095 <para>By default, every new volume is assigned a space quota of 5000
2096 KB blocks unless you include the <emphasis
2097 role="bold">-maxquota</emphasis> argument to the <emphasis
2098 role="bold">vos create</emphasis> command. Also by default, the ACL
2099 on the root directory of every new volume grants all permissions to
2100 the members of the <emphasis
2101 role="bold">system:administrators</emphasis> group. To learn how to
2102 change these values when creating an account with individual
2103 commands, see <link linkend="HDRWQ503">To create one user account
2104 with individual commands</link>. When using <emphasis
2105 role="bold">uss</emphasis> commands to create accounts, you can
2106 specify alternate ACL and quota values in the template file's
2107 <emphasis role="bold">V</emphasis> instruction; see <link
2108 linkend="HDRWQ473">Creating a Volume with the V
2109 Instruction</link>.</para>
2112 <primary>server machine</primary>
2114 <secondary>configuration issues</secondary>
2118 <primary>configuring</primary>
2120 <secondary>file server machine, issues</secondary>
2124 <primary>roles for server machine</primary>
2126 <secondary>summary</secondary>
2130 <primary>server machine</primary>
2132 <secondary>roles for</secondary>
2134 <tertiary>summary</tertiary>
2138 <primary>server machine</primary>
2140 <secondary>first installed</secondary>
2145 <sect1 id="HDRWQ51">
2146 <title>Configuring Server Machines</title>
2148 <para>This section discusses some issues to consider when configuring
2149 server machines, which store AFS data, transfer it to client machines
2150 on request, and house the AFS administrative databases. To learn about
2151 client machines, see <link linkend="HDRWQ54">Configuring Client
2152 Machines</link>.</para>
2154 <para>If your cell has more than one AFS server machine, you can
2155 configure them to perform specialized functions. A machine can assume
2156 one or more of the roles described in the following list. For more
2157 details, see <link linkend="HDRWQ90">The Four Roles for File Server
2161 <para>A <emphasis>simple file server</emphasis> machine runs
2162 only the processes that store and deliver AFS files to client
2163 machines. You can run as many simple file server machines as you
2164 need to satisfy your cell's performance and disk space
2165 requirements.</para>
2169 <para>A <emphasis>database server machine</emphasis> runs the
2170 four database server processes that maintain AFS's replicated
2171 administrative databases: the Authentication, Backup,
2172 Protection, and Volume Location (VL) Server processes.</para>
2176 <para>A <emphasis>binary distribution machine</emphasis>
2177 distributes the AFS server binaries for its system type to all
2178 other server machines of that system type.</para>
2182 <para>The single <emphasis>system control machine</emphasis>
2183 distributes common server configuration files to all other
2184 server machines in the cell.
2190 <para>The <emphasis>OpenAFS Quick Beginnings</emphasis> explains how
2191 to configure your cell's first file server machine to assume all four
2192 roles. The <emphasis>OpenAFS Quick Beginnings</emphasis> chapter on
2193 installing additional server machines also explains how to configure
2194 them to perform one or more roles.</para>
2197 <primary>database server machine</primary>
2199 <secondary>reason to run three</secondary>
2203 <primary>distribution</primary>
2205 <secondary>of databases</secondary>
2209 <primary>databases, distributed</primary>
2213 <primary>distributed databases</primary>
2216 <sect2 id="HDRWQ52">
2217 <title>Replicating the OpenAFS Administrative Databases</title>
2219 <para>The AFS administrative databases are housed on database server
2220 machines and store information that is crucial for correct cell
2221 functioning. Both server processes and Cache Managers access the
2222 information frequently:
2225 <para>Every time a Cache Manager fetches a file from a
2226 directory that it has not previously accessed, it must look up
2227 the file's location in the Volume Location Database
2232 <para>Every time a user obtains an AFS token from the
2233 Authentication Server, the server looks up the user's password
2234 in the Authentication Database.</para>
2238 <para>The first time that a user accesses a volume housed on a
2239 specific file server machine, the File Server contacts the
2240 Protection Server for a list of the user's group memberships
2241 as recorded in the Protection Database.</para>
2245 <para>Every time you back up a volume using the AFS Backup
2246 System, the Backup Server creates records for it in the Backup
2252 <para>Maintaining your cell is simplest if the first machine has the
2253 lowest IP address of any machine you plan to use as a database
2254 server machine. If you later decide to use a machine with a lower IP
2255 address as a database server machine, you must update the <emphasis
2256 role="bold">CellServDB</emphasis> file on all clients before
2257 introducing the new machine.</para>
2259 <para>If your cell has more than one server machine, it is best to
2260 run more than one as a database server machine (but more than three
2261 are rarely necessary). Replicating the administrative databases in
2262 this way yields the same benefits as replicating volumes: increased
2263 availability and reliability. If one database server machine or
2264 process stops functioning, the information in the database is still
2265 available from others. The load of requests for database information
2266 is spread across multiple machines, preventing any one from becoming
2269 <para>Unlike replicated volumes, however, replicated databases do
2270 change frequently. Consistent system performance demands that all
2271 copies of the database always be identical, so it is not acceptable
2272 to record changes in only some of them. To synchronize the copies of
2273 a database, the database server processes use AFS's distributed
2274 database technology, Ubik. See <link linkend="HDRWQ102">Replicating
2275 the OpenAFS Administrative Databases</link>.</para>
2277 <para>If your cell has only one file server machine, it must also
2278 serve as a database server machine. If you cell has two file server
2279 machines, it is not always advantageous to run both as database
2280 server machines. If a server, process, or network failure interrupts
2281 communications between the database server processes on the two
2282 machines, it can become impossible to update the information in the
2283 database because neither of them can alone elect itself as the
2284 synchronization site.</para>
2287 <primary>server machine</primary>
2289 <secondary>protecting directories on local disk</secondary>
2293 <primary>local disk</primary>
2295 <secondary>protecting on file server machine</secondary>
2299 <sect2 id="HDRWQ53">
2300 <title>AFS Files on the Local Disk</title>
2302 <para>It is generally simplest to store the binaries for all AFS
2303 server processes in the <emphasis
2304 role="bold">/usr/afs/bin</emphasis> directory on every file server
2305 machine, even if some processes do not actively run on the
2306 machine. This makes it easier to reconfigure a machine to fill a new
2309 <para>For security reasons, the <emphasis
2310 role="bold">/usr/afs</emphasis> directory on a file server machine
2311 and all of its subdirectories and files must be owned by the local
2312 superuser <emphasis role="bold">root</emphasis> and have only the
2313 first <emphasis role="bold">w</emphasis> (<emphasis
2314 role="bold">write</emphasis>) mode bit turned on. Some files even
2315 have only the first <emphasis role="bold">r</emphasis> (<emphasis
2316 role="bold">read</emphasis>) mode bit turned on (for example, the
2317 <emphasis role="bold">/usr/afs/etc/KeyFile</emphasis> file, which
2318 lists the AFS server encryption keys). Each time the BOS Server
2319 starts, it checks that the mode bits on certain files and
2320 directories match the expected values. For a list, see the
2321 <emphasis>OpenAFS Quick Beginnings</emphasis> section about
2322 protecting sensitive AFS directories, or the discussion of the
2323 output from the <emphasis role="bold">bos status</emphasis> command
2324 in <link linkend="HDRWQ159">To display the status of server
2325 processes and their BosConfig entries</link>.</para>
2327 <para>For a description of the contents of all AFS directories on a
2328 file server machine's local disk, see <link
2329 linkend="HDRWQ80">Administering Server Machines</link>.</para>
2332 <sect2 id="Header_62">
2333 <title>Configuring Partitions to Store AFS Data</title>
2335 <para>The partitions that house AFS volumes on a file server machine
2336 must be mounted at directories named</para>
2339 role="bold">/vicep</emphasis><emphasis>index</emphasis></para>
2341 <para>where <emphasis>index</emphasis> is one or two lowercase
2342 letters. By convention, the first AFS partition created is mounted
2343 at the <emphasis role="bold">/vicepa</emphasis> directory, the
2344 second at the <emphasis role="bold">/vicepb</emphasis> directory,
2345 and so on through the <emphasis role="bold">/vicepz</emphasis>
2346 directory. The names then continue with <emphasis
2347 role="bold">/vicepaa</emphasis> through <emphasis
2348 role="bold">/vicepaz</emphasis>, <emphasis
2349 role="bold">/vicepba</emphasis> through <emphasis
2350 role="bold">/vicepbz</emphasis>, and so on, up to the maximum
2351 supported number of server partitions, which is specified in the
2352 OpenAFS Release Notes.</para>
2354 <para>Each <emphasis role="bold">/vicep</emphasis>x directory must
2355 correspond to an entire partition or logical volume, and must be a
2356 subdirectory of the root directory (/). It is not acceptable to
2357 configure part of (for example) the <emphasis
2358 role="bold">/usr</emphasis> partition as an AFS server partition and
2359 mount it on a directory called <emphasis
2360 role="bold">/usr/vicepa</emphasis>.</para>
2362 <para>Also, do not store non-AFS files on AFS server partitions. The
2363 File Server and Volume Server expect to have available all of the
2364 space on the partition. Sharing space also creates competition
2365 between AFS and the local UNIX file system for access to the
2366 partition, particularly if the UNIX files are frequently
2370 <primary>server machine</primary>
2372 <secondary>monitoring</secondary>
2376 <primary>file server machine</primary>
2378 <secondary>rebooting, about</secondary>
2382 <primary>rebooting</primary>
2384 <secondary>file server machine, limiting</secondary>
2388 <primary>weekly restart of BOS Server (automatic)</primary>
2390 <secondary>about</secondary>
2394 <primary>restart times for BOS Server</primary>
2396 <secondary>about</secondary>
2400 <sect2 id="Header_63">
2401 <title>Monitoring, Rebooting and Automatic Process Restarts</title>
2403 <para>AFS provides several tools for monitoring the File Server,
2404 including the <emphasis role="bold">scout</emphasis> and <emphasis
2405 role="bold">afsmonitor</emphasis> programs. You can configure them
2406 to alert you when certain threshold values are exceeded, for example
2407 when a server partition is more than 95% full. See <link
2408 linkend="HDRWQ323">Monitoring and Auditing AFS
2409 Performance</link>.</para>
2411 <para>Rebooting a file server machine requires shutting down the AFS
2412 processes and so inevitably causes a service outage. Reboot file
2413 server machines as infrequently as possible. For instructions, see
2414 <link linkend="HDRWQ139">Rebooting a Server Machine</link>.</para>
2416 <para>The BOS Server checks each morning at 5:00 a.m. for any newly
2417 installed binary files in the <emphasis
2418 role="bold">/usr/afs/bin</emphasis> directory. It compares the
2419 timestamp on each binary file to the time at which the corresponding
2420 process last restarted. If the timestamp on the binary is later, the
2421 BOS Server restarts the corresponding process to start using
2424 <para>The BOS server also supports performing a weekly restart of
2425 all AFS server processes, including itself. This functionality is
2426 disabled on new installs, but historically it was set to 4:00am on
2427 Sunday. Administrators may find that installations predating OpenAFS
2428 1.6.0 have weekly restarts enabled.</para>
2430 <para>The default times are in the early morning hours when the
2431 outage that results from restarting a process is likely to disturb
2432 the fewest number of people. You can display the restart times for
2433 each machine with the <emphasis role="bold">bos
2434 getrestart</emphasis> command, and set them with the <emphasis
2435 role="bold">bos setrestart</emphasis> command. The latter command
2436 enables you to disable automatic restarts entirely, by setting the
2437 time to <emphasis role="bold">never</emphasis>. See <link
2438 linkend="HDRWQ171">Setting the BOS Server's Restart
2439 Times</link>.</para>
2442 <primary>client machine</primary>
2444 <secondary>configuration issues</secondary>
2448 <primary>configuring</primary>
2450 <secondary>client machine, issues</secondary>
2455 <sect1 id="HDRWQ54">
2456 <title>Configuring Client Machines</title>
2458 <para>This section summarizes issues to consider as you install and
2459 configure client machines in your cell.</para>
2462 <primary>client machine</primary>
2464 <secondary>files required on local disk</secondary>
2468 <primary>local disk</primary>
2470 <secondary>files required on client machine</secondary>
2474 <primary>file</primary>
2476 <secondary>required on client machine local disk</secondary>
2479 <sect2 id="HDRWQ55">
2480 <title>Configuring the Local Disk</title>
2482 <para>You can often free up significant amounts of local disk space
2483 on AFS client machines by storing standard UNIX files in AFS and
2484 creating symbolic links to them from the local disk. The <emphasis
2485 role="bold">@sys</emphasis> pathname variable can be useful in links
2486 to system-specific files; see <link linkend="HDRWQ56">Using the @sys
2487 Variable in Pathnames</link>.</para>
2489 <para>There are two types of files that must actually reside on the
2490 local disk: boot sequence files needed before the <emphasis
2491 role="bold">afsd</emphasis> program is invoked, and files that can
2492 be helpful during file server machine outages.</para>
2494 <para>During a reboot, AFS is inaccessible until the <emphasis
2495 role="bold">afsd</emphasis> program executes and initializes the
2496 Cache Manager. (In the conventional configuration, the AFS
2497 initialization file is included in the machine's initialization
2498 sequence and invokes the <emphasis role="bold">afsd</emphasis>
2499 program.) Files needed during reboot prior to that point must reside
2500 on the local disk. They include the following, but this list is not
2501 necessarily exhaustive.
2504 <para>Standard UNIX utilities including the following or their
2508 <para>Machine initialization files (stored in the
2509 <emphasis role="bold">/etc</emphasis> or <emphasis
2510 role="bold">/sbin</emphasis> directory on many system
2515 <para>The <emphasis role="bold">fstab</emphasis>
2520 <para>The <emphasis role="bold">mount</emphasis> command
2525 <para>The <emphasis role="bold">umount</emphasis>
2526 command binary</para>
2533 <para>All subdirectories and files in the <emphasis
2534 role="bold">/usr/vice</emphasis> directory, including the
2539 role="bold">/usr/vice/cache</emphasis> directory</para>
2544 role="bold">/usr/vice/etc/afsd</emphasis> command
2550 role="bold">/usr/vice/etc/cacheinfo</emphasis> file</para>
2555 role="bold">/usr/vice/etc/CellServDB</emphasis>
2561 role="bold">/usr/vice/etc/ThisCell</emphasis> file</para>
2566 <para>For more information on these files, see <link
2567 linkend="HDRWQ391">Configuration and Cache-Related Files on
2568 the Local Disk</link>.</para>
2573 <para>The other type of files and programs to retain on the local
2574 disk are those you need when diagnosing and fixing problems caused
2575 by a file server outage, because the outage can make inaccessible
2576 the copies stored in AFS. Examples include the binaries for a text
2577 editor (such as <emphasis role="bold">ed</emphasis> or <emphasis
2578 role="bold">vi</emphasis>) and for the <emphasis
2579 role="bold">fs</emphasis> and <emphasis role="bold">bos</emphasis>
2580 commands. Store copies of AFS command binaries in the <emphasis
2581 role="bold">/usr/vice/etc</emphasis> directory as well as including
2582 them in the <emphasis role="bold">/usr/afsws</emphasis> directory,
2583 which is normally a link into AFS. Then place the <emphasis
2584 role="bold">/usr/afsws</emphasis> directory before the <emphasis
2585 role="bold">/usr/vice/etc</emphasis> directory in users'
2586 <envar>PATH</envar> environment variable definition. When AFS is
2587 functioning normally, users access the copy in the <emphasis
2588 role="bold">/usr/afsws</emphasis> directory, which is more likely to
2589 be current than a local copy.</para>
2592 <sect2 id="Header_66">
2593 <title>Enabling Access to Foreign Cells</title>
2596 <primary>client machine</primary>
2598 <secondary>enabling access to foreign cell</secondary>
2601 <para>As detailed in <link linkend="HDRWQ39">Making Other Cells
2602 Visible in Your Cell</link>, you enable the Cache Manager to access
2603 a cell's AFS filespace by storing a list of the cell's database
2604 server machines in the local <emphasis
2605 role="bold">/usr/vice/etc/CellServDB</emphasis> file. The Cache
2606 Manager reads the list into kernel memory at reboot for faster
2607 retrieval. You can change the list in kernel memory between reboots
2608 by using the <emphasis role="bold">fs newcell</emphasis> command.</para>
2610 <para>Because each client machine maintains its own copy of the
2611 <emphasis role="bold">CellServDB</emphasis> file, you can in theory
2612 enable access to different foreign cells on different client
2613 machines. This is not usually practical, however, especially if
2614 users do not always work on the same machine.</para>
2617 <primary>at-sys (@sys) variable in pathnames</primary>
2621 <primary>sys (@sys) variable in pathnames</primary>
2625 <primary>variables</primary>
2627 <secondary>@sys in pathnames</secondary>
2631 <sect2 id="HDRWQ56">
2632 <title>Using the @sys Variable in Pathnames</title>
2634 <para>When creating symbolic links into AFS on the local disk, it is
2635 often practical to use the @sys variable in pathnames. The Cache
2636 Manager automatically substitutes the local machine's AFS system
2637 name (CPU/operating system type) for the @sys variable. This means
2638 you can place the same links on machines of various system types and
2639 still have each machine access the binaries for its system type. For
2640 example, the Cache Manager on a machine running AIX 4.2 converts
2641 <emphasis role="bold">/afs/example.com/@sys</emphasis> to <emphasis
2642 role="bold">/afs/example.com/rs_aix42</emphasis>, whereas a machine
2643 running Solaris 10 converts it to <emphasis
2644 role="bold">/afs/example.com/sun4x_510</emphasis>.</para>
2646 <para>If you want to use the @sys variable, it is simplest to use
2647 the conventional AFS system type names as specified in the OpenAFS
2648 Release Notes. The Cache Manager records the local machine's system
2649 type name in kernel memory during initialization. If you do not use
2650 the conventional names, you must use the <emphasis role="bold">fs
2651 sysname</emphasis> command to change the value in kernel memory from
2652 its default just after Cache Manager initialization, on every client
2653 machine of the relevant system type. The <emphasis role="bold">fs
2654 sysname</emphasis> command also displays the current value; see
2655 <link linkend="HDRWQ417">Displaying and Setting the System Type
2658 <para>In pathnames in the AFS filespace itself, use the @sys
2659 variable carefully and sparingly, because it can lead to unexpected
2660 results. It is generally best to restrict its use to only one level
2661 in the filespace. The third level is a common choice, because that
2662 is where many cells store the binaries for different machine
2665 <para>Multiple instances of the @sys variable in a pathname are
2666 especially dangerous to people who must explicitly change
2667 directories (with the <emphasis role="bold">cd</emphasis> command,
2668 for example) into directories that store binaries for system types
2669 other than the machine on which they are working, such as
2670 administrators or developers who maintain those directories. After
2671 changing directories, it is recommended that such people verify they
2672 are in the desired directory.</para>
2675 <sect2 id="Header_68">
2676 <title>Setting Server Preferences</title>
2678 <para>The Cache Manager stores a table of preferences for file
2679 server machines in kernel memory. A preference rank pairs a file
2680 server machine interface's IP address with an integer in the range
2681 from 1 to 65,534. When it needs to access a file, the Cache Manager
2682 compares the ranks for the interfaces of all machines that house the
2683 file, and first attempts to access the file via the interface with
2684 the best rank. As it initializes, the Cache Manager sets default
2685 ranks that bias it to access files via interfaces that are close to
2686 it in terms of network topology. You can adjust the preference ranks
2687 to improve performance if you wish.</para>
2689 <para>The Cache Manager also uses similar preferences for Volume
2690 Location (VL) Server machines. Use the <emphasis role="bold">fs
2691 getserverprefs</emphasis> command to display preference ranks and
2692 the <emphasis role="bold">fs setserverprefs</emphasis> command to
2693 set them. See <link linkend="HDRWQ414">Maintaining Server Preference
2694 Ranks</link>.</para>
2697 <primary>user account</primary>
2699 <secondary>configuration issues</secondary>
2703 <sect1 id="HDRWQ57">
2704 <title>Configuring AFS User Accounts</title>
2706 <para>This section discusses some of the issues to consider when
2707 configuring AFS user accounts. Because AFS is separate from the UNIX
2708 file system, a user's AFS account is separate from her UNIX
2711 <para>The preferred method for creating a user account is with the
2712 <emphasis role="bold">uss</emphasis> suite of commands. With a single
2713 command, you can create all the components of one or many accounts,
2714 after you have prepared a template file that guides the account
2715 creation. See <link linkend="HDRWQ449">Creating and Deleting User
2716 Accounts with the uss Command Suite</link>.</para>
2718 <para>Alternatively, you can issue the individual commands that create
2719 each component of an account. For instructions, along with
2720 instructions for removing user accounts and changing user passwords,
2721 user volume quotas and usernames, see <link
2722 linkend="HDRWQ491">Administering User Accounts</link>.</para>
2724 <para>When users leave your system, it is often good policy to remove
2725 their accounts. Instructions appear in <link
2726 linkend="HDRWQ486">Deleting Individual Accounts with the uss delete
2727 Command</link> and <link linkend="HDRWQ524">Removing a User
2728 Account</link>.</para>
2730 <para>An AFS user account consists of the following components, which
2731 are described in greater detail in <link linkend="HDRWQ494">The
2732 Components of an AFS User Account</link>.
2735 <para>A Protection Database entry</para>
2739 <para>An Authentication Database entry</para>
2743 <para>A volume</para>
2747 <para>A home directory at which the volume is mounted</para>
2751 <para>Ownership of the home directory and full permissions on
2756 <para>An entry in the local password file (<emphasis
2757 role="bold">/etc/passwd</emphasis> or equivalent) of each
2758 machine the user needs to log into</para>
2762 <para>Optionally, standard files and subdirectories that make
2763 the account more useful</para>
2768 <para>By creating some components but not others, you can create
2769 accounts at different levels of functionality, using either <emphasis
2770 role="bold">uss</emphasis> commands as described in <link
2771 linkend="HDRWQ449">Creating and Deleting User Accounts with the uss
2772 Command Suite</link> or individual commands as described in <link
2773 linkend="HDRWQ491">Administering User Accounts</link>. The levels of
2774 functionality include the following
2777 <para>An authentication-only account enables the user to obtain
2778 AFS tokens and so to access protected AFS data and to issue
2779 privileged commands. It consists only of entries in the
2780 Authentication and Protection Database. This type of account is
2781 suitable for administrative accounts and for users from foreign
2782 cells who need to access protected data. Local users generally
2783 also need a volume and home directory.</para>
2787 <para>A basic user account includes a volume for the user, in
2788 addition to Authentication and Protection Database entries. The
2789 volume is mounted in the AFS filespace as the user's home
2790 directory, and provides a repository for the user's personal
2795 <para>A full account adds configuration files for basic
2796 functions such as logging in, printing, and mail delivery to a
2797 basic account, making it more convenient and useful. For a
2798 discussion of some useful types of configuration files, see
2799 <link linkend="HDRWQ60">Creating Standard Files in New AFS
2800 Accounts</link>.</para>
2805 <para>If your users have UNIX user accounts that predate the
2806 introduction of AFS in the cell, you possibly want to convert them
2807 into AFS accounts. There are three main issues to consider:
2810 <para>Making UNIX and AFS UIDs match</para> </listitem>
2813 <para>Setting the password field in the local password file
2814 appropriately</para>
2818 <para>Moving files from the UNIX file system into AFS</para>
2823 <para>For further discussion, see <link linkend="HDRWQ459">Converting
2824 Existing UNIX Accounts with uss</link> or <link
2825 linkend="HDRWQ498">Converting Existing UNIX Accounts</link>.</para>
2828 <primary>username</primary>
2830 <secondary>choosing</secondary>
2834 <primary>user</primary>
2836 <secondary>name</secondary>
2842 <primary>choosing</primary>
2844 <secondary>name</secondary>
2846 <tertiary>user</tertiary>
2850 <primary>anonymous user</primary>
2852 <secondary>AFS UID reserved</secondary>
2856 <primary>AFS UID</primary>
2858 <secondary>reserved</secondary>
2860 <tertiary>anonymous user</tertiary>
2863 <sect2 id="HDRWQ58">
2864 <title>Choosing Usernames and Naming Other Account
2867 <para>This section suggests schemes for choosing usernames, AFS
2868 UIDs, user volume names and mount point names, and also outlines
2869 some restrictions on your choices.</para>
2872 <title>Usernames</title>
2874 <para>AFS imposes very few restrictions on the form of
2875 usernames. It is best to keep usernames short, both because many
2876 utilities and applications can handle usernames of no more than
2877 eight characters and because by convention many components of and
2878 AFS account incorporate the name. These include the entries in the
2879 Protection and Authentication Databases, the volume, and the mount
2880 point. Depending on your electronic mail delivery system, the
2881 username can become part of the user's mailing address. The
2882 username is also the string that the user types when logging in to
2883 a client machine.</para>
2886 <para>Some common choices for usernames are last names, first names,
2887 initials, or a combination, with numbers sometimes added. It is
2888 also best to avoid using the following characters, many of which
2889 have special meanings to the command shell.
2892 <para>The comma (<emphasis role="bold">,</emphasis>)</para>
2896 <para>The colon (<emphasis role="bold">:</emphasis>), because
2897 AFS reserves it as a field separator in protection group
2898 names; see <link linkend="HDRWQ62">The Two Types of
2899 User-Defined Groups</link></para>
2903 <para>The semicolon (<emphasis
2904 role="bold">;</emphasis>)</para>
2908 <para>The "at-sign" (<emphasis role="bold">@</emphasis>); this
2909 character is reserved for Internet mailing addresses</para>
2917 <para>The newline character</para>
2921 <para>The period (<emphasis role="bold">.</emphasis>); it is
2922 conventional to use this character only in the special
2923 username that an administrator adopts while performing
2924 privileged tasks, such as <emphasis
2925 role="bold">pat.admin</emphasis></para>
2931 <title>AFS UIDs and UNIX UIDs</title>
2933 <para>AFS associates a unique identification number, the AFS UID,
2934 with every username, recording the mapping in the user's
2935 Protection Database entry. The AFS UID functions within AFS much
2936 as the UNIX UID does in the local file system: the AFS server
2937 processes and the Cache Manager use it internally to identify a
2938 user, rather than the username.</para>
2941 <para>Every AFS user also must have a UNIX UID recorded in the local
2942 password file (<emphasis role="bold">/etc/passwd</emphasis> or
2943 equivalent) of each client machine they log onto. Both
2944 administration and a user's AFS access are simplest if the AFS UID
2945 and UNIX UID match. One important consequence of matching UIDs is
2946 that the owner reported by the <emphasis role="bold">ls
2947 -l</emphasis> command matches the AFS username.</para>
2949 <para>It is usually best to allow the Protection Server to allocate
2950 the AFS UID as it creates the Protection Database entry. However,
2951 both the <emphasis role="bold">pts createuser</emphasis> command and
2952 the <emphasis role="bold">uss</emphasis> commands that create user
2953 accounts enable you to assign AFS UIDs explicitly. This is
2954 appropriate in two cases:
2957 <para>You wish to group together the AFS UIDs of related
2962 <para>You are converting an existing UNIX account into an AFS
2963 account and want to make the AFS UID match the existing UNIX
2969 <para>After the Protection Server initializes for the first time on
2970 a cell's first file server machine, it starts assigning AFS UIDs at
2971 a default value. To change the default before creating any user
2972 accounts, or at any time, use the <emphasis role="bold">pts
2973 setmax</emphasis> command to reset the <computeroutput>max user id
2974 counter</computeroutput>. To display the counter, use the <emphasis
2975 role="bold">pts listmax</emphasis> command. See <link
2976 linkend="HDRWQ560">Displaying and Setting the AFS UID and GID
2977 Counters</link>.</para>
2979 <para>AFS reserves one AFS UID, 32766, for the user <emphasis
2980 role="bold">anonymous</emphasis>. The AFS server processes assign
2981 this identity and AFS UID to any user who does not possess a token
2982 for the local cell. Do not assign this AFS UID to any other user or
2983 hardcode its current value into any programs or a file's owner
2984 field, because it is subject to change in future releases.</para>
2987 <primary>username</primary>
2989 <secondary>part of volume name</secondary>
2993 <primary>choosing</primary>
2995 <secondary>name</secondary>
2997 <tertiary>user volume</tertiary>
3001 <title>User Volume Names</title>
3003 <para>Like any volume name, a user volume's base (read/write) name
3004 cannot exceed 22 characters in length or include the <emphasis
3005 role="bold">.readonly</emphasis> or <emphasis
3006 role="bold">.backup</emphasis> extension. See <link
3007 linkend="HDRWQ44">Creating Volumes to Simplify
3008 Administration</link>. By convention, user volume names have the
3009 format <emphasis role="bold">user.</emphasis>username. Using the
3010 <emphasis role="bold">user.</emphasis> prefix not only makes it
3011 easy to identify the volume's contents, but also to create a
3012 backup version of all user volumes by issuing a single <emphasis
3013 role="bold">vos backupsys</emphasis> command.</para>
3017 <primary>mount point</primary>
3019 <secondary>choosing name for user volume</secondary>
3023 <primary>choosing</primary>
3025 <secondary>name</secondary>
3027 <tertiary>user volume mount point</tertiary>
3031 <title>Mount Point Names</title>
3033 <para>By convention, the mount point for a user's volume is named
3034 after the username. Many cells follow the convention of mounting
3035 user volumes in the <emphasis
3036 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
3037 role="bold">/usr</emphasis> directory, as discussed in <link
3038 linkend="HDRWQ43">The Third Level</link>. Very large cells
3039 sometimes find that mounting all user volumes in the same
3040 directory slows directory lookup, however; for suggested
3041 alternatives, see the following section.</para>
3045 <primary>directories</primary>
3047 <secondary>for grouping user home directories</secondary>
3051 <primary>user account</primary>
3053 <secondary>suggestions for grouping home directories</secondary>
3057 <sect2 id="HDRWQ59">
3058 <title>Grouping Home Directories</title>
3060 <para>Mounting user volumes in the <emphasis
3061 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
3062 role="bold">/usr</emphasis> directory is an AFS-appropriate
3063 variation on the standard UNIX practice of putting user home
3064 directories under the <emphasis role="bold">/usr</emphasis>
3065 subdirectory. However, cells with more than a few hundred users
3066 sometimes find that mounting all user volumes in a single directory
3067 results in slow directory lookup. The solution is to distribute user
3068 volume mount points into several directories; there are a number of
3069 alternative methods to accomplish this.
3072 <para>Distribute user home directories into multiple
3073 directories that reflect organizational divisions, such as
3074 academic or corporate departments. For example, a company can
3075 create group directories called <emphasis
3076 role="bold">usr/marketing</emphasis>, <emphasis
3077 role="bold">usr/research</emphasis>, <emphasis
3078 role="bold">usr/finance</emphasis>. A good feature of this
3079 scheme is that knowing a user's department is enough to find
3080 the user's home directory. Also, it makes it easy to set the
3081 ACL to limit access to members of the department only. A
3082 potential drawback arises if departments are of sufficiently
3083 unequal size that users in large departments experience slower
3084 lookup than users in small departments. This scheme is also
3085 not appropriate in cells where users frequently change between
3090 <para>Distribute home directories into alphabetic
3091 subdirectories of the <emphasis role="bold">usr</emphasis>
3092 directory (the <emphasis role="bold">usr/a</emphasis>
3093 subdirectory, the <emphasis role="bold">usr/b</emphasis>
3094 subdirectory, and so on), based on the first letter of the
3095 username. If the cell is very large, create subdirectories
3096 under each letter that correspond to the second letter in the
3097 user name. This scheme has the same advantages and
3098 disadvantages of a department-based scheme. Anyone who knows
3099 the user's username can find the user's home directory, but
3100 users with names that begin with popular letters sometimes
3101 experience slower lookup.</para>
3105 <para>Distribute home directories randomly but evenly into
3106 more than one grouping directory. One cell that uses this
3107 scheme has over twenty such directories called the <emphasis
3108 role="bold">usr1</emphasis> directory, the <emphasis
3109 role="bold">usr2</emphasis> directory, and so on. This scheme
3110 is especially appropriate in cells where the other two schemes
3111 do not seem feasible. It eliminates the potential problem of
3112 differences in lookup speed, because all directories are about
3113 the same size. Its disadvantage is that there is no way to
3114 guess which directory a given user's volume is mounted in, but
3115 a solution is to create a symbolic link in the regular
3116 <emphasis role="bold">usr</emphasis> directory that references
3117 the actual mount point. For example, if user <emphasis
3118 role="bold">smith</emphasis>'s volume is mounted at the
3120 role="bold">/afs/bigcell.example.com/usr17/smith</emphasis>
3121 directory, then the <emphasis
3122 role="bold">/afs/bigcell.example.com/usr/smith</emphasis>
3123 directory is a symbolic link to the <emphasis
3124 role="bold">../usr17/smith</emphasis> directory. This way, if
3125 someone does not know which directory the user <emphasis
3126 role="bold">smith</emphasis> is in, he or she can access it
3127 through the link called <emphasis
3128 role="bold">usr/smith</emphasis>; people who do know the
3129 appropriate directory save lookup time by specifying
3135 <para>For instructions on how to implement the various schemes when
3136 using the <emphasis role="bold">uss</emphasis> program to create
3137 user accounts, see <link linkend="HDRWQ472">Evenly Distributing User
3138 Home Directories with the G Instruction</link> and <link
3139 linkend="HDRWQ473">Creating a Volume with the V
3140 Instruction</link>.</para>
3143 <sect2 id="Header_72">
3144 <title>Making a Backup Version of User Volumes Available</title>
3146 <para>Mounting the backup version of a user's volume is a simple way
3147 to enable users themselves to restore data they have accidentally
3148 removed or deleted. It is conventional to mount the backup version
3149 at a subdirectory of the user's home directory (called perhaps the
3150 <emphasis role="bold">OldFiles</emphasis> subdirectory), but other
3151 schemes are possible. Once per day you create a new backup version
3152 to capture the changes made that day, overwriting the previous day's
3153 backup version with the new one. Users can always retrieve the
3154 previous day's copy of a file without your assistance, freeing you
3155 to deal with more pressing tasks.</para>
3157 <para>Users sometimes want to delete the mount point to their backup
3158 volume, because they erroneously believe that the backup volume's
3159 contents count against their quota. Remind them that the backup
3160 volume is separate, so the only space it uses in the user volume is
3161 the amount needed for the mount point.</para>
3163 <para>For further discussion of backup volumes, see <link
3164 linkend="HDRWQ77">Backing Up AFS Data</link> and <link
3165 linkend="HDRWQ201">Creating Backup Volumes</link>.</para>
3168 <primary>file</primary>
3170 <secondary>creating standard ones in new user account</secondary>
3174 <primary>user account</primary>
3176 <secondary>creating</secondary>
3178 <tertiary>standard files in</tertiary>
3182 <primary>creating</primary>
3184 <secondary>standard files in new user account</secondary>
3188 <sect2 id="HDRWQ60">
3189 <title>Creating Standard Files in New AFS Accounts</title>
3191 <para>From your experience as a UNIX administrator, you are probably
3192 familiar with the use of login and shell initialization files (such
3193 as the <emphasis role="bold">.login</emphasis> and <emphasis
3194 role="bold">.cshrc</emphasis> files) to make an account easier to
3197 <para>It is often practical to add some AFS-specific directories to
3198 the definition of the user's <envar>PATH</envar> environment
3199 variable, including the following:
3202 <para>The path to a <emphasis role="bold">bin</emphasis>
3203 subdirectory in the user's home directory for binaries the
3204 user has created (that is, <emphasis
3205 role="bold">/afs/</emphasis><replaceable>cellname</replaceable><emphasis
3206 role="bold">/usr/</emphasis><replaceable>username</replaceable><emphasis
3207 role="bold">/bin</emphasis>)</para>
3211 <para>The <emphasis role="bold">/usr/afsws/bin</emphasis>
3212 path, which conventionally includes programs like <emphasis
3213 role="bold">fs</emphasis>, <emphasis
3214 role="bold">klog</emphasis>, <emphasis
3215 role="bold">kpasswd</emphasis>, <emphasis
3216 role="bold">pts</emphasis>, <emphasis
3217 role="bold">tokens</emphasis>, and <emphasis
3218 role="bold">unlog</emphasis></para>
3222 <para>The <emphasis role="bold">/usr/afsws/etc</emphasis>
3223 path, if the user is an administrator; it usually houses the
3224 AFS command suites that require privilege (the <emphasis
3225 role="bold">backup</emphasis>, <emphasis
3226 role="bold">butc</emphasis>, <emphasis
3227 role="bold">kas</emphasis>, <emphasis
3228 role="bold">uss</emphasis>, <emphasis
3229 role="bold">vos</emphasis> commands), and others.</para>
3234 <para>If you are not using an AFS-modified login utility, it can be
3235 helpful to users to invoke the <emphasis role="bold">klog</emphasis>
3236 command in their <emphasis role="bold">.login</emphasis> file so
3237 that they obtain AFS tokens as part of logging in. In the following
3238 example command sequence, the first line echoes the string
3239 <computeroutput>klog</computeroutput> to the standard output stream,
3240 so that the user understands the purpose of the
3241 <computeroutput>Password:</computeroutput> prompt that appears when
3242 the second line is executed. The <emphasis
3243 role="bold">-setpag</emphasis> flag associates the new tokens with a
3244 process authentication group (PAG), which is discussed further in
3245 <link linkend="HDRWQ64">Identifying AFS Tokens by PAG</link>.</para>
3248 echo -n "klog " klog -setpag
3251 <para>The following sequence of commands has a similar effect,
3252 except that the <emphasis role="bold">pagsh</emphasis> command forks
3253 a new shell with which the PAG and tokens are associated.</para>
3256 pagsh echo -n "klog " klog
3259 <para>If you use an AFS-modified login utility, this sequence is not
3260 necessary, because such utilities both log a user in locally and
3261 obtain AFS tokens.</para>
3264 <primary>group</primary>
3266 <secondary>AFS GID</secondary>
3270 <primary>group</primary>
3272 <secondary>restrictions</secondary>
3276 <primary>group</primary>
3278 <secondary>privacy flags</secondary>
3282 <primary>privacy flags on Protection Database entry</primary>
3287 <sect1 id="HDRWQ61">
3288 <title>Using AFS Protection Groups</title>
3290 <para>AFS enables users to define their own groups of other users or
3291 machines. The groups are placed on ACLs to grant the same permissions
3292 to many users without listing each user individually. For group
3293 creation instructions, see <link linkend="HDRWQ531">Administering the
3294 Protection Database</link>.</para>
3296 <para>Groups have AFS ID numbers, just as users do, but an AFS group
3297 ID (GID) is a negative integer whereas a user's AFS UID is a positive
3298 integer. By default, the Protection Server allocates a new group's AFS
3299 GID automatically, but members of the <emphasis
3300 role="bold">system:administrators</emphasis> group can assign a GID
3301 when issuing the <emphasis role="bold">pts creategroup</emphasis>
3302 command. Before explicitly assigning a GID, it is best to verify that
3303 it is not already in use.</para>
3305 <para>A group cannot belong to another group, but it can own another
3306 group or even itself as long as it (the owning group) has at least one
3307 member. The current owner of a group can transfer ownership of the
3308 group to another user or group, even without the new owner's
3309 permission. At that point the former owner loses administrative
3310 control over the group.</para>
3312 <para>By default, each user can create 20 groups. A system
3313 administrator can increase or decrease this group creation quota with
3314 the <emphasis role="bold">pts setfields</emphasis> command.</para>
3316 <para>Each Protection Database entry (group or user) is protected by a
3317 set of five privacy flagswhich limit who can administer the entry and
3318 what they can do. The default privacy flags are fairly restrictive,
3319 especially for user entries. See <link linkend="HDRWQ559">Setting the
3320 Privacy Flags on Database Entries</link>.</para>
3323 <primary>system:administrators group</primary>
3325 <secondary>about</secondary>
3329 <primary>system:anyuser group</primary>
3331 <secondary>about</secondary>
3335 <primary>system:authuser group</primary>
3337 <secondary>about</secondary>
3341 <primary>group</primary>
3343 <secondary>system-defined</secondary>
3346 <sect2 id="Header_75">
3347 <title>The Three System Groups</title>
3349 <para>As the Protection Server initializes for the first time on a
3350 cell's first database server machine, it automatically creates three
3351 group entries: the <emphasis role="bold">system:anyuser</emphasis>,
3352 <emphasis role="bold">system:authuser</emphasis>, and <emphasis
3353 role="bold">system:administrators</emphasis> groups.</para>
3356 <primary>AFS UID</primary>
3358 <secondary>reserved</secondary>
3360 <tertiary>system-defined groups</tertiary>
3363 <para>The first two system groups are unlike any other groups in the
3364 Protection Database in that they do not have a stable membership:
3367 <para>The <emphasis role="bold">system:anyuser</emphasis>
3368 group includes everyone who can access a cell's AFS filespace:
3369 users who have tokens for the local cell, users who have
3370 logged in on a local AFS client machine but not obtained
3371 tokens (such as the local superuser <emphasis
3372 role="bold">root</emphasis>), and users who have connected to
3373 a local machine from outside the cell. Placing the <emphasis
3374 role="bold">system:anyuser</emphasis> group on an ACL grants
3375 access to the widest possible range of users. It is the only
3376 way to extend access to users from foreign AFS cells that do
3377 not have local accounts.</para>
3381 <para>The <emphasis role="bold">system:authuser</emphasis>
3382 group includes everyone who has a valid token obtained from
3383 the cell's AFS authentication service.</para>
3388 <para>Because the groups do not have a stable membership, the
3389 <emphasis role="bold">pts membership</emphasis> command produces no
3390 output for them. Similarly, they do not appear in the list of groups
3391 to which a user belongs.</para>
3393 <para>The <emphasis role="bold">system:administrators</emphasis>
3394 group does have a stable membership, consisting of the cell's
3395 privileged administrators. Members of this group can issue any
3396 <emphasis role="bold">pts</emphasis> command, and are the only ones
3397 who can issue several other restricted commands (such as the
3398 <emphasis role="bold">chown</emphasis> command on AFS files). By
3399 default, they also implicitly have the <emphasis
3400 role="bold">a</emphasis> (<emphasis
3401 role="bold">administer</emphasis>) and <emphasis
3402 role="bold">l</emphasis> (<emphasis role="bold">lookup</emphasis>)
3403 permissions on every ACL in the filespace. For information about
3404 changing this default, see <link linkend="HDRWQ586">Administering
3405 the system:administrators Group</link>.</para>
3407 <para>For a discussion of how to use system groups effectively on
3408 ACLs, see <link linkend="HDRWQ571">Using Groups on
3412 <sect2 id="HDRWQ62">
3413 <title>The Two Types of User-Defined Groups</title>
3415 <para>All users can create regular groups. A regular group name has
3416 two fields separated by a colon, the first of which must indicate
3417 the group's ownership. The Protection Server refuses to create or
3418 change the name of a group if the result does not accurately
3419 indicate the ownership.</para>
3421 <para>Members of the <emphasis
3422 role="bold">system:administrators</emphasis> group can create
3423 prefix-less groups whose names do not have the first field that
3424 indicates ownership. For suggestions on using the two types of
3425 groups effectively, see <link linkend="HDRWQ545">Using Groups
3426 Effectively</link>.</para>
3429 <primary>authentication</primary>
3431 <secondary>AFS separate from UNIX</secondary>
3435 <primary>AFS</primary>
3437 <secondary>authentication separate from UNIX</secondary>
3442 <sect1 id="HDRWQ63">
3443 <title>Login and Authentication in AFS</title>
3445 <para>As explained in <link linkend="HDRWQ31">Differences in
3446 Authentication</link>, AFS authentication is separate from UNIX
3447 authentication because the two file systems are separate. The
3448 separation has two practical implications:
3451 <para>To access AFS files, users must both log into the local
3452 file system and authenticate with the AFS authentication
3453 service. (Logging into the local file system is necessary
3454 because the only way to access the AFS filespace is through a
3455 Cache Manager, which resides in the local machine's
3460 <para>Passwords are stored in two separate places: in the
3461 Kerberos Database for AFS and in the each machine's local
3462 password file (the <emphasis role="bold">/etc/passwd</emphasis>
3463 file or equivalent) for the local file system.</para>
3468 <para>When a user successfully authenticates, the AFS authentication
3469 service passes a token to the user's Cache Manager. The token is a
3470 small collection of data that certifies that the user has correctly
3471 provided the password associated with a particular AFS identity. The
3472 Cache Manager presents the token to AFS server processes along with
3473 service requests, as proof that the user is genuine. To learn about
3474 the mutual authentication procedure they use to establish identity,
3475 see <link linkend="HDRWQ75">A More Detailed Look at Mutual
3476 Authentication</link>.</para>
3478 <para>The Cache Manager stores tokens in the user's credential
3479 structure in kernel memory. To distinguish one user's credential
3480 structure from another's, the Cache Manager identifies each one either
3481 by the user's UNIX UID or by a process authentication group (PAG),
3482 which is an identification number guaranteed to be unique in the
3483 cell. For further discussion, see <link linkend="HDRWQ64">Identifying
3484 AFS Tokens by PAG</link>.</para>
3487 <primary>tokens</primary>
3489 <secondary>one-per-cell rule</secondary>
3492 <para>A user can have only one token per cell in each separately
3493 identified credential structure. To obtain a second token for the same
3494 cell, the user must either log into a different machine or obtain
3495 another credential structure with a different identifier than any
3496 existing credential structure, which is most easily accomplished by
3497 issuing the <emphasis role="bold">pagsh</emphasis> command (see <link
3498 linkend="HDRWQ64">Identifying AFS Tokens by PAG</link>). In a single
3499 credential structure, a user can have one token for each of many cells
3500 at the same time. As this implies, authentication status on one
3501 machine or PAG is independent of authentication status on another
3502 machine or PAG, which can be very useful to a user or system
3503 administrator.</para>
3505 <para>The AFS distribution includes library files that enable each
3506 system type's login utility to authenticate users with AFS and log
3507 them into the local file system in one step. If you do not configure
3508 an AFS-modified login utility on a client machine, its users must
3509 issue the <emphasis role="bold">klog</emphasis> command to
3510 authenticate with AFS after logging in.</para>
3513 <para>The AFS-modified libraries do not necessarily support all
3514 features available in an operating system's proprietary login
3515 utility. In some cases, it is not possible to support a utility at
3516 all. For more information about the supported utilities in each AFS
3517 version, see the OpenAFS Release Notes.</para>
3521 <primary>commands</primary>
3523 <secondary>pagsh</secondary>
3527 <primary>pagsh command</primary>
3531 <primary>commands</primary>
3533 <secondary>klog with -setpag flag</secondary>
3537 <primary>klog command</primary>
3539 <secondary>with -setpag flag</secondary>
3543 <primary>PAG</primary>
3545 <secondary>creating with klog or pagsh command</secondary>
3549 <primary>creating</primary>
3551 <secondary>PAG with klog or pagsh command</secondary>
3555 <primary>process authentication group</primary>
3557 <secondary></secondary>
3562 <sect2 id="HDRWQ64">
3563 <title>Identifying AFS Tokens by PAG</title>
3565 <para>As noted, the Cache Manager identifies user credential
3566 structures either by UNIX UID or by PAG. Using a PAG is preferable
3567 because it guaranteed to be unique: the Cache Manager allocates it
3568 based on a counter that increments with each use. In contrast,
3569 multiple users on a machine can share or assume the same UNIX UID,
3570 which creates potential security problems. The following are two
3571 common such situations:
3574 <para>The local superuser <emphasis
3575 role="bold">root</emphasis> can always assume any other user's
3576 UNIX UID simply by issuing the <emphasis
3577 role="bold">su</emphasis> command, without providing the
3578 user's password. If the credential structure is associated
3579 with the user's UNIX UID, then assuming the UID means
3580 inheriting the AFS tokens.</para>
3584 <para>Two users working on different NFS client machines can
3585 have the same UNIX UID in their respective local file
3586 systems. If they both access the same NFS/AFS Translator
3587 machine, and the Cache Manager there identifies them by their
3588 UNIX UID, they become indistinguishable. To eliminate this
3589 problem, the Cache Manager on a translator machine
3590 automatically generates a PAG for each user and uses it,
3591 rather than the UNIX UID, to tell users apart.</para>
3596 <para>Yet another advantage of PAGs over UIDs is that processes
3597 spawned by the user inherit the PAG and so share the token; thus
3598 they gain access to AFS as the authenticated user. In many
3599 environments, for example, printer and other daemons run under
3600 identities (such as the local superuser <emphasis
3601 role="bold">root</emphasis>) that the AFS server processes recognize
3602 only as the <emphasis role="bold">anonymous</emphasis> user. Unless
3603 PAGs are used, such daemons cannot access files for which the
3604 <emphasis role="bold">system:anyuser</emphasis> group does not have
3605 the necessary ACL permissions.</para>
3607 <para>Once a user has a PAG, any new tokens the user obtains are
3608 associated with the PAG. The PAG expires two hours after any
3609 associated tokens expire or are discarded. If the user issues the
3610 <emphasis role="bold">klog</emphasis> command before the PAG
3611 expires, the new token is associated with the existing PAG (the PAG
3612 is said to be recycled in this case).</para>
3614 <para>AFS-modified login utilities automatically generate a PAG, as
3615 described in the following section. If you use a standard login
3616 utility, your users must issue the <emphasis
3617 role="bold">pagsh</emphasis> command before the <emphasis
3618 role="bold">klog</emphasis> command, or include the latter command's
3619 <emphasis role="bold">-setpag</emphasis> flag. For instructions, see
3620 <link linkend="HDRWQ69">Using Two-Step Login and
3621 Authentication</link>.</para>
3623 <para>Users can also use either command at any time to create a new
3624 PAG. The difference between the two commands is that the <emphasis
3625 role="bold">klog</emphasis> command replaces the PAG associated with
3626 the current command shell and tokens. The <emphasis
3627 role="bold">pagsh</emphasis> command initializes a new command shell
3628 before creating a new PAG. If the user already had a PAG, any
3629 running processes or jobs continue to use the tokens associated with
3630 the old PAG whereas any new jobs or processes use the new PAG and
3631 its associated tokens. When you exit the new shell (by pressing
3632 <<emphasis role="bold">Ctrl-d</emphasis>>, for example), you
3633 return to the original PAG and shell. By default, the <emphasis
3634 role="bold">pagsh</emphasis> command initializes a Bourne shell, but
3635 you can include the <emphasis role="bold">-c</emphasis> argument to
3636 initialize a C shell (the <emphasis role="bold">/bin/csh</emphasis>
3637 program on many system types) or Korn shell (the <emphasis
3638 role="bold">/bin/ksh</emphasis> program) instead.</para>
3641 <primary>login utility</primary>
3643 <secondary>AFS version</secondary>
3647 <sect2 id="HDRWQ65">
3648 <title>Using an AFS-modified login Utility</title>
3650 <para>As previously mentioned, an AFS-modified login utility
3651 simultaneously obtains an AFS token and logs the user into the local
3652 file system. This section outlines the login and authentication
3653 process and its interaction with the value in the password field of
3654 the local password file.</para>
3656 <para>An AFS-modified login utility performs a sequence of steps
3657 similar to the following; details can vary for different operating
3661 <para>It checks the user's entry in the local password file
3662 (the <emphasis role="bold">/etc/passwd</emphasis> file or
3667 <para>If no entry exists, or if an asterisk
3668 (<computeroutput>*</computeroutput>) appears in the entry's
3669 password field, the login attempt fails. If the entry exists,
3670 the attempt proceeds to the next step.</para>
3673 <listitem id="LIWQ66">
3674 <para>The utility obtains a PAG.</para>
3677 <listitem id="LIWQ67">
3678 <para>The utility converts the password
3679 provided by the user into an encryption key and encrypts a
3680 packet of data with the key. It sends the packet to the AFS
3681 authentication service (the AFS Authentication Server in the
3682 conventional configuration).</para>
3686 <para>The authentication service decrypts the packet and,
3687 depending on the success of the decryption, judges the
3688 password to be correct or incorrect. (For more details, see
3689 <link linkend="HDRWQ75">A More Detailed Look at Mutual
3690 Authentication</link>.)
3693 <para>If the authentication service judges the password
3694 incorrect, the user does not receive an AFS token. The
3695 PAG is retained, ready to be associated with any tokens
3696 obtained later. The attempt proceeds to Step <link
3697 linkend="LIWQ68">6</link>.</para>
3701 <para>If the authentication service judges the password
3702 correct, it issues a token to the user as proof of AFS
3703 authentication. The login utility logs the user into the
3704 local UNIX file system. Some login utilities echo the
3705 following banner to the screen to alert the user to
3706 authentication with AFS. Step <link
3707 linkend="LIWQ68">6</link> is skipped.
3709 AFS(R) version Login
3717 <listitem id="LIWQ68">
3718 <para>If no AFS token was granted in
3719 Step <link linkend="LIWQ67">4</link>, the login utility
3720 attempts to log the user into the local file system, by
3721 comparing the password provided to the local password file.
3724 <para>If the password is incorrect or any value other
3725 than an encrypted 13-character string appears in the
3726 password field, the login attempt fails.</para>
3730 <para>If the password is correct, the user is logged
3731 into the local file system only.</para> </listitem>
3739 <primary>local password file</primary>
3741 <secondary>when using AFS--modified login utility</secondary>
3745 <primary>login utility</primary>
3747 <secondary>AFS version's interaction with local password
3752 <primary>password</primary>
3754 <secondary>local password file</secondary>
3757 <para>As indicated, when you use an AFS-modified login utility, the
3758 password field in the local password file is no longer the primary
3759 gate for access to your system. If the user provides the correct AFS
3760 password, then the program never consults the local password
3761 file. However, you can still use the password field to control
3762 access, in the following way:
3765 <para>To prevent both local login and AFS authentication,
3766 place an asterisk (<emphasis role="bold">*</emphasis>) in the
3767 field. This is useful mainly in emergencies, when you want to
3768 prevent a certain user from logging into the machine.</para>
3772 <para>To prevent login to the local file system if the user
3773 does not provide the correct AFS password, place a character
3774 string of any length other than the standard thirteen
3775 characters in the field. This is appropriate if you want to
3776 permit only people with local AFS accounts to login on your
3777 machines. A single <emphasis role="bold">X</emphasis> or other
3778 character is the most easily recognizable way to do
3783 <para>To enable a user to log into the local file system even
3784 after providing an incorrect AFS password, record a standard
3785 UNIX encrypted password in the field by issuing the standard
3786 UNIX password-setting command (<emphasis
3787 role="bold">passwd</emphasis> or equivalent).</para>
3792 <para>Systems that use a Pluggable Authentication Module (PAM) for
3793 login and AFS authentication do not necessarily consult the local
3794 password file at all, in which case they do not use the password
3795 field to control authentication and login attempts. Instead,
3796 instructions in the PAM configuration file (on many system types,
3797 <emphasis role="bold">/etc/pam.conf</emphasis>) fill the same
3798 function. See the instructions in the OpenAFS Quick Beginnings for
3799 installing AFS-modified login utilities.</para>
3802 <primary>local password file</primary>
3804 <secondary>when not using AFS-modified login utility</secondary>
3808 <sect2 id="HDRWQ69">
3809 <title>Using Two-Step Login and Authentication</title>
3811 <para>In cells that do not use an AFS-modified login utility, users
3812 must issue separate commands to login and authenticate, as detailed
3813 in the OpenAFS User Guide:
3816 <para>They use the standard <emphasis
3817 role="bold">login</emphasis> program to login to the local
3818 file system, providing the password listed in the local
3819 password file (the <emphasis
3820 role="bold">/etc/passwd</emphasis> file or equivalent).</para>
3824 <para>They must issue the <emphasis
3825 role="bold">klog</emphasis> command to authenticate with the
3826 AFS authentication service, including its <emphasis
3827 role="bold">-setpag</emphasis> flag to associate the new
3828 tokens with a process authentication group (PAG).</para>
3833 <para>As mentioned in <link linkend="HDRWQ60">Creating Standard
3834 Files in New AFS Accounts</link>, you can invoke the <emphasis
3835 role="bold">klog -setpag</emphasis> command in a user's <emphasis
3836 role="bold">.login</emphasis> file (or equivalent) so that the user
3837 does not have to remember to issue the command after logging in. The
3838 user still must type a password twice, once at the prompt generated
3839 by the login utility and once at the <emphasis
3840 role="bold">klog</emphasis> command's prompt. This implies that the
3841 two passwords can differ, but it is less confusing if they do
3844 <para>Another effect of not using an AFS-modified login utility is
3845 that the AFS servers recognize the standard <emphasis
3846 role="bold">login</emphasis> program as the <emphasis
3847 role="bold">anonymous</emphasis> user. If the <emphasis
3848 role="bold">login</emphasis> program needs to access any AFS files
3849 (such as the <emphasis role="bold">.login</emphasis> file in a
3850 user's home directory), then the ACL that protects the file must
3851 include an entry granting the <emphasis role="bold">l</emphasis>
3852 (<emphasis role="bold">lookup</emphasis>) and <emphasis
3853 role="bold">r</emphasis> (<emphasis role="bold">read</emphasis>)
3854 permissions to the <emphasis role="bold">system:anyuser</emphasis>
3857 <para>When you do not use an AFS-modified login utility, an actual
3858 (scrambled) password must appear in the local password file for each
3859 user. Use the <emphasis role="bold">/bin/passwd</emphasis> file to
3860 insert or change these passwords. It is simpler if the password in
3861 the local password file matches the AFS password, but it is not
3865 <primary>tokens</primary>
3867 <secondary>displaying for user</secondary>
3871 <primary>tokens</primary>
3873 <secondary>command</secondary>
3877 <primary>commands</primary>
3879 <secondary>tokens</secondary>
3883 <primary>listing</primary>
3885 <secondary>tokens held by issuer</secondary>
3889 <primary>commands</primary>
3891 <secondary>klog</secondary>
3895 <primary>klog command</primary>
3899 <primary>server process</primary>
3901 <secondary>creating ticket (tokens) for</secondary>
3905 <primary>tickets</primary>
3907 <secondary></secondary>
3913 <primary>tokens</primary>
3915 <secondary>creating for server process</secondary>
3919 <primary>authenticated identity</primary>
3921 <secondary>acquiring with klog command</secondary>
3925 <primary>unlog command</primary>
3929 <primary>commands</primary>
3931 <secondary>unlog</secondary>
3935 <primary>discarding</primary>
3937 <secondary>tokens</secondary>
3941 <primary>tokens</primary>
3943 <secondary>discarding with unlog command</secondary>
3947 <sect2 id="Header_81">
3948 <title>Obtaining, Displaying, and Discarding Tokens</title>
3950 <para>Once logged in, a user can obtain a token at any time with the
3951 <emphasis role="bold">klog</emphasis> command. If a valid token
3952 already exists, the new one overwrites it. If a PAG already exists,
3953 the new token is associated with it.</para>
3955 <para>By default, the <emphasis role="bold">klog</emphasis> command
3956 authenticates the issuer using the identity currently logged in to
3957 the local file system. To authenticate as a different identity, use
3958 the <emphasis role="bold">-principal</emphasis> argument. To obtain
3959 a token for a foreign cell, use the <emphasis
3960 role="bold">-cell</emphasis> argument (it can be combined with the
3961 <emphasis role="bold">-principal</emphasis> argument). See the
3962 OpenAFS User Guide and the entry for the <emphasis
3963 role="bold">klog</emphasis> command in the OpenAFS Administration
3966 <para>To discard either all tokens or the token for a particular
3967 cell, issue the <emphasis role="bold">unlog</emphasis> command. The
3968 command affects only the tokens associated with the current command
3969 shell. See the OpenAFS User Guideand the entry for the <emphasis
3970 role="bold">unlog</emphasis> command in the OpenAFS Administration
3973 <para>To display the tokens associated with the current command
3974 shell, issue the <emphasis role="bold">tokens</emphasis>
3975 command. The following examples illustrate its output in various
3978 <para>If the issuer is not authenticated in any cell:</para>
3981 % <emphasis role="bold">tokens</emphasis>
3982 Tokens held by the Cache Manager:
3986 <para>The following shows the output for a user with AFS UID 1000 in
3987 the Example Corporation cell:</para>
3990 % <emphasis role="bold">tokens</emphasis>
3991 Tokens held by the Cache Manager:
3992 User's (AFS ID 1000) tokens for afs@example.com [Expires Jun 2 10:00]
3996 <para>The following shows the output for a user who is authenticated
3997 in Example Corporation cell, the Example Organization cell and the
3998 Example Network cell. The user has different AFS UIDs in the three
3999 cells. Tokens for the last cell are expired:</para>
4002 % <emphasis role="bold">tokens</emphasis>
4003 Tokens held by the Cache Manager:
4004 User's (AFS ID 1000) tokens for afs@example.com [Expires Jun 2 10:00]
4005 User's (AFS ID 4286) tokens for afs@example.org [Expires Jun 3 1:34]
4006 User's (AFS ID 22) tokens for afs@example.net [>>Expired<<]
4010 <para>The Kerberos version of the <emphasis
4011 role="bold">tokens</emphasis> command (the <emphasis
4012 role="bold">tokens.krb</emphasis> command), also reports information
4013 on the ticket-granting ticket, including the ticket's owner, the
4014 ticket-granting service, and the expiration date, as in the
4015 following example. Also see <link linkend="HDRWQ70">Support for
4016 Kerberos Authentication</link>.</para>
4019 % <emphasis role="bold">tokens.krb</emphasis>
4020 Tokens held by the Cache Manager:
4021 User's (AFS ID 1000) tokens for afs@example.com [Expires Jun 2 10:00]
4022 User smith's tokens for krbtgt.EXAMPLE.COM@example.com [Expires Jun 2 10:00]
4027 <sect2 id="Header_82">
4028 <title>Setting Default Token Lifetimes for Users</title>
4031 <primary>tokens</primary>
4033 <secondary>setting default lifetimes for users</secondary>
4036 <para>The maximum lifetime of a user token is the smallest of the
4037 ticket lifetimes recorded in the following three Authentication
4038 Database entries. The <emphasis role="bold">kas examine</emphasis>
4039 command reports the lifetime as <computeroutput>Max ticket
4040 lifetime</computeroutput>. Administrators who have the
4041 <computeroutput>ADMIN</computeroutput> flag on their Authentication
4042 Database entry can use the <emphasis
4043 role="bold">-lifetime</emphasis> argument to the <emphasis
4044 role="bold">kas setfields</emphasis> command to set an entry's
4048 <para>The <emphasis role="bold">afs</emphasis> entry, which
4049 corresponds to the AFS server processes. The default is 100
4054 <para>The <emphasis role="bold">krbtgt</emphasis>.cellname
4055 entry, which corresponds to the ticket-granting ticket used
4056 internally in generating the token. The default is 720 hours
4061 <para>The entry for the user of the AFS-modified login utility
4062 or issuer of the <emphasis role="bold">klog</emphasis>
4063 command. The default is 25 hours for user entries created
4064 using the AFS 3.1 or later version of the Authentication
4065 Server, and 100 hours for user entries created using the AFS
4066 3.0 version of the Authentication Server. A user can use the
4067 <emphasis role="bold">kas examine</emphasis> command to
4068 display his or her own Authentication Database entry.</para>
4074 <para>An AFS-modified login utility always grants a token with a
4075 lifetime calculated from the previously described three
4076 values. When issuing the <emphasis role="bold">klog</emphasis>
4077 command, a user can request a lifetime shorter than the default by
4078 using the <emphasis role="bold">-lifetime</emphasis> argument. For
4079 further information, see the OpenAFS User Guide and the <emphasis
4080 role="bold">klog</emphasis> reference page in the OpenAFS
4081 Administration Reference.</para>
4085 <sect2 id="Header_83">
4086 <title>Changing Passwords</title>
4089 <primary>password</primary>
4091 <secondary>changing in AFS</secondary>
4095 <primary>kpasswd command</primary>
4099 <primary>commands</primary>
4101 <secondary>kpasswd</secondary>
4105 <primary>kas commands</primary>
4107 <secondary>setpassword</secondary>
4111 <primary>commands</primary>
4113 <secondary>kas setpassword</secondary>
4116 <para>Regular AFS users can change their own passwords by using
4117 either the <emphasis role="bold">kpasswd</emphasis> or <emphasis
4118 role="bold">kas setpassword</emphasis> command. The commands prompt
4119 for the current password and then twice for the new password, to
4120 screen out typing errors.</para>
4122 <para>Administrators who have the
4123 <computeroutput>ADMIN</computeroutput> flag on their Authentication
4124 Database entries can change any user's password, either by using the
4125 <emphasis role="bold">kpasswd</emphasis> command (which requires
4126 knowing the current password) or the <emphasis role="bold">kas
4127 setpassword</emphasis> command.</para>
4129 <para>If your cell does not use an AFS-modified login utility,
4130 remember also to change the local password, using the operating
4131 system's password-changing command. For more instructions on
4132 changing passwords, see <link linkend="HDRWQ516">Changing AFS
4133 Passwords</link>.</para>
4136 <sect2 id="Header_84">
4137 <title>Imposing Restrictions on Passwords and Authentication
4140 <para>You can help to make your cell more secure by imposing
4141 restrictions on user passwords and authentication attempts. To
4142 impose the restrictions as you create an account, use the <emphasis
4143 role="bold">A</emphasis> instruction in the <emphasis
4144 role="bold">uss</emphasis> template file as described in <link
4145 linkend="HDRWQ478">Increasing Account Security with the A
4146 Instruction</link>. To set or change the values on an existing
4147 account, use the <emphasis role="bold">kas setfields</emphasis>
4148 command as described in <link linkend="HDRWQ515">Improving Password
4149 and Authentication Security</link>.</para>
4152 <primary>password</primary>
4154 <secondary>expiration</secondary>
4158 <primary>password</primary>
4160 <secondary>lifetime</secondary>
4164 <primary>kas commands</primary>
4166 <secondary>setfields</secondary>
4170 <primary>commands</primary>
4172 <secondary>kas setfields</secondary>
4176 <primary>Authentication Database</primary>
4178 <secondary>password lifetime, setting</secondary>
4182 <primary>password</primary>
4184 <secondary>restricting reuse</secondary>
4187 <para>By default, AFS passwords never expire. Limiting password
4188 lifetime can help improve security by decreasing the time the
4189 password is subject to cracking attempts. You can choose an lifetime
4190 from 1 to 254 days after the password was last changed. It
4191 automatically applies to each new password as it is set. When the
4192 user changes passwords, you can also insist that the new password is
4193 not similar to any of the 20 passwords previously used.</para>
4196 <primary>password</primary>
4198 <secondary>consequences of multiple failed authentication
4199 attempts</secondary>
4203 <primary>kas commands</primary>
4205 <secondary>setfields</secondary>
4209 <primary>commands</primary>
4211 <secondary>kas setfields</secondary>
4215 <primary>authentication</primary>
4217 <secondary>consequences of multiple failures</secondary>
4220 <para>Unscrupulous users can try to gain access to your AFS cell by
4221 guessing an authorized user's password. To protect against this type
4222 of attack, you can limit the number of times that a user can
4223 consecutively fail to provide the correct password. When the limit
4224 is exceeded, the authentication service refuses further
4225 authentication attempts for a specified period of time (the lockout
4226 time). To reenable authentication attempts before the lockout time
4227 expires, an administrator must issue the <emphasis role="bold">kas
4228 unlock</emphasis> command.</para>
4231 <primary>password</primary>
4233 <secondary>checking quality of</secondary>
4237 <primary>kpasswd command</primary>
4241 <primary>commands</primary>
4243 <secondary>kpasswd</secondary>
4247 <primary>kas commands</primary>
4249 <secondary>setpassword</secondary>
4253 <primary>kpwvalid program</primary>
4256 <para>In addition to settings on user's authentication accounts, you
4257 can improve security by automatically checking the quality of new
4258 user passwords. The <emphasis role="bold">kpasswd</emphasis> and
4259 <emphasis role="bold">kas setpassword</emphasis> commands pass the
4260 proposed password to a program or script called <emphasis
4261 role="bold">kpwvalid</emphasis>, if it exists. The <emphasis
4262 role="bold">kpwvalid</emphasis> performs quality checks and returns
4263 a code to indicate whether the password is acceptable. You can
4264 create your own program or modified the sample program included in
4265 the AFS distribution. See the <emphasis
4266 role="bold">kpwvalid</emphasis> reference page in the OpenAFS
4267 Administration Reference.</para>
4269 <para>There are several types of quality checks that can improve
4273 <para>The password is a minimum length</para>
4277 <para>The password is not a word</para>
4281 <para>The password contains both numbers and letters</para>
4287 <sect2 id="HDRWQ70">
4288 <title>Support for Kerberos Authentication</title>
4291 <primary>Kerberos</primary>
4293 <secondary>support for in AFS</secondary>
4297 <primary>commands</primary>
4299 <secondary>klog.krb</secondary>
4303 <primary>commands</primary>
4305 <secondary>pagsh.krb</secondary>
4309 <primary>commands</primary>
4311 <secondary>tokens.krb</secondary>
4315 <primary>klog.krb command</primary>
4319 <primary>pagsh.krb command</primary>
4323 <primary>tokens.krb command</primary>
4326 <para>If your site is using standard Kerberos authentication rather
4327 than the AFS Authentication Server, use the modified versions of the
4328 <emphasis role="bold">klog</emphasis>, <emphasis
4329 role="bold">pagsh</emphasis>, and <emphasis
4330 role="bold">tokens</emphasis> commands that support Kerberos
4331 authentication. The binaries for the modified version of these
4332 commands have the same name as the standard binaries with the
4333 addition of a <emphasis role="bold">.krb</emphasis>
4336 <para>Use either the Kerberos version or the standard command
4337 throughout the cell; do not mix the two versions. AFS Product
4338 Support can provide instructions on installing the Kerberos version
4339 of these four commands. For information on the differences between
4340 the two versions of these commands, see the OpenAFS Administration
4344 <sect1 id="HDRWQ71">
4345 <title>Security and Authorization in AFS</title>
4347 <para>AFS incorporates several features to ensure that only authorized
4348 users gain access to data. This section summarizes the most important
4349 of them and suggests methods for improving security in your
4352 <sect2 id="HDRWQ72">
4353 <title>Some Important Security Features</title>
4356 <primary>security</primary>
4358 <secondary>AFS features</secondary>
4362 <primary>AFS</primary>
4364 <secondary>security features</secondary>
4368 <title>ACLs on Directories</title>
4370 <para>Files in AFS are protected by the access control list (ACL)
4371 associated with their parent directory. The ACL defines which
4372 users or groups can access the data in the directory, and in what
4373 way. See <link linkend="HDRWQ562">Managing Access Control
4374 Lists</link>.</para>
4378 <title>Mutual Authentication Between Client and Server</title>
4380 <para>When an AFS client and server process communicate, each
4381 requires the other to prove its identity during mutual
4382 authentication, which involves the exchange of encrypted
4383 information that only valid parties can decrypt and respond
4384 to. For a detailed description of the mutual authentication
4385 process, see <link linkend="HDRWQ75">A More Detailed Look at
4386 Mutual Authentication</link>.</para>
4389 <para>AFS server processes mutually authenticate both with one
4390 another and with processes that represent human users. After mutual
4391 authentication is complete, the server and client have established
4392 an authenticated connection, across which they can communicate
4393 repeatedly without having to authenticate again until the connection
4394 expires or one of the parties closes it. Authenticated connections
4395 have varying lifetimes.</para>
4398 <title>Tokens</title>
4400 <para>In order to access AFS files, users must prove their
4401 identities to the AFS authentication service by providing the
4402 correct AFS password. If the password is correct, the
4403 authentication service sends the user a token as evidence of
4404 authenticated status. See <link linkend="HDRWQ63">Login and
4405 Authentication in AFS</link>.</para>
4408 <para>Servers assign the user identity <emphasis
4409 role="bold">anonymous</emphasis> to users and processes that do not
4410 have a valid token. The <emphasis role="bold">anonymous</emphasis>
4411 identity has only the access granted to the <emphasis
4412 role="bold">system:anyuser</emphasis> group on ACLs.</para>
4415 <title>Authorization Checking</title>
4417 <para>Mutual authentication establishes that two parties
4418 communicating with one another are actually who they claim to be.
4419 For many functions, AFS server processes also check that the
4420 client whose identity they have verified is also authorized to
4421 make the request. Different requests require different kinds of
4422 privilege. See <link linkend="HDRWQ73">Three Types of
4423 Privilege</link>.</para>
4427 <title>Encrypted Network Communications</title>
4430 <primary>network</primary>
4432 <secondary>encrypted communication in AFS</secondary>
4436 <primary>encrypted network communication</primary>
4440 <primary>security</primary>
4442 <secondary>encrypted network communication</secondary>
4445 <para>The AFS server processes encrypt particularly sensitive
4446 information before sending it back to clients. Even if an
4447 unauthorized party is able to eavesdrop on an authenticated
4448 connection, they cannot decipher encrypted data without the proper
4452 <para>The following AFS commands encrypt data because they involve
4453 server encryption keys and passwords:
4456 <para>The <emphasis role="bold">bos addkey</emphasis> command,
4457 which adds a server encryption key to the <emphasis
4458 role="bold">/usr/afs/etc/KeyFile</emphasis> file</para>
4462 <para>The <emphasis role="bold">bos listkeys</emphasis>
4463 command, which lists the server encryption keys from the
4464 <emphasis role="bold">/usr/afs/etc/KeyFile</emphasis>
4469 <para>The <emphasis role="bold">kpasswd</emphasis> command,
4470 which changes a password in the Authentication Database</para>
4474 <para>Most commands in the <emphasis
4475 role="bold">kas</emphasis> command suite</para>
4480 <para>In addition, the Update Server
4481 encrypts sensitive information (such as the contents of <emphasis
4482 role="bold">KeyFile</emphasis>) when distributing it. Other commands
4483 in the <emphasis role="bold">bos</emphasis> suite and the commands
4484 in the <emphasis role="bold">fs</emphasis>, <emphasis
4485 role="bold">pts</emphasis> and <emphasis role="bold">vos</emphasis>
4486 suites do not encrypt data before transmitting it.</para>
4489 <sect2 id="HDRWQ73">
4490 <title>Three Types of Privilege</title>
4492 <para>AFS uses three separate types of privilege for the reasons
4493 discussed in <link linkend="HDRWQ585">The Reason for Separate
4497 <para>Membership in the <emphasis
4498 role="bold">system:administrators</emphasis> group. Members
4499 are entitled to issue any <emphasis role="bold">pts</emphasis>
4500 command and those <emphasis role="bold">fs</emphasis> commands
4501 that set volume quota. By default, they also implicitly have
4502 the <emphasis role="bold">a</emphasis> (<emphasis
4503 role="bold">administer</emphasis>) and <emphasis
4504 role="bold">l</emphasis> (<emphasis
4505 role="bold">lookup</emphasis>) permissions on every ACL in the
4506 file tree even if the ACL does not include an entry for
4511 <para>The <computeroutput>ADMIN</computeroutput> flag on the
4512 Authentication Database entry. An administrator with this flag
4513 can issue any <emphasis role="bold">kas</emphasis>
4518 <para>Inclusion in the <emphasis
4519 role="bold">/usr/afs/etc/UserList</emphasis> file. An
4520 administrator whose username appears in this file can issue
4521 any <emphasis role="bold">bos</emphasis>, <emphasis
4522 role="bold">vos</emphasis>, or <emphasis
4523 role="bold">backup</emphasis> command (although some <emphasis
4524 role="bold">backup</emphasis> commands require additional
4525 privilege as described in <link linkend="HDRWQ260">Granting
4526 Administrative Privilege to Backup Operators</link>).</para>
4532 <sect2 id="Header_89">
4533 <title>Authorization Checking versus Authentication</title>
4535 <para>AFS distinguishes between authentication and authorization
4536 checking. Authentication refers to the process of proving
4537 identity. Authorization checking refers to the process of verifying
4538 that an authenticated identity is allowed to perform a certain
4541 <para>AFS implements authentication at the level of
4542 connections. Each time two parties establish a new connection, they
4543 mutually authenticate. In general, each issue of an AFS command
4544 establishes a new connection between AFS server process and
4547 <para>AFS implements authorization checking at the level of server
4548 machines. If authorization checking is enabled on a server machine,
4549 then all of the server processes running on it provide services only
4550 to authorized users. If authorization checking is disabled on a
4551 server machine, then all of the server processes perform any action
4552 for anyone. Obviously, disabling authorization checking is an
4553 extreme security exposure. For more information, see <link
4554 linkend="HDRWQ123">Managing Authentication and Authorization
4555 Requirements</link>.</para>
4558 <sect2 id="HDRWQ74">
4559 <title>Improving Security in Your Cell</title>
4562 <primary>security</primary>
4564 <secondary>suggestions for improving</secondary>
4567 <para>You can improve the level of security in your cell by
4568 configuring user accounts, server machines, and system administrator
4569 accounts in the indicated way.</para>
4572 <title>User Accounts</title>
4577 <para>Use an AFS-modified login utility, or include the
4578 <emphasis role="bold">-setpag</emphasis> flag to the
4579 <emphasis role="bold">klog</emphasis> command, to associate
4580 the credential structure that houses tokens with a PAG
4581 rather than a UNIX UID. This prevents users from inheriting
4582 someone else's tokens by assuming their UNIX identity. For
4583 further discussion, see <link linkend="HDRWQ64">Identifying
4584 AFS Tokens by PAG</link>.</para>
4588 <para>Encourage users to issue the <emphasis
4589 role="bold">unlog</emphasis> command to destroy their tokens
4590 before logging out. This forestalls attempts to access
4591 tokens left behind kernel memory. Consider including the
4592 <emphasis role="bold">unlog</emphasis> command in every
4593 user's <emphasis role="bold">.logout</emphasis> file or
4601 <title>Server Machines</title>
4606 <para>Disable authorization checking only in emergencies or
4607 for very brief periods of time. It is best to work at the
4608 console of the affected machine during this time, to prevent
4609 anyone else from accessing the machine through the
4614 <para>Change the AFS server encryption key on a frequent and
4615 regular schedule. Make it difficult to guess (a long string
4616 including nonalphabetic characters, for instance). Unlike
4617 user passwords, the password from which the AFS key is
4618 derived can be longer than eight characters, because it is
4619 never used during login. The <emphasis role="bold">kas
4620 setpassword</emphasis> command accepts a password hundreds
4621 of characters long. For instructions, see <link
4622 linkend="HDRWQ355">Managing Server Encryption
4627 <para>As much as possible, limit the number of people who
4628 can login at a server machine's console or remotely.
4629 Imposing this limit is an extra security precaution rather
4630 than a necessity. The machine cannot serve as an AFS client
4631 in this case.</para>
4635 <para>Particularly limit access to the local superuser
4636 <emphasis role="bold">root</emphasis> account on a server
4637 machine. The local superuser <emphasis
4638 role="bold">root</emphasis> has free access to important
4639 administrative subdirectories of the <emphasis
4640 role="bold">/usr/afs</emphasis> directory, as described in
4641 <link linkend="HDRWQ53">AFS Files on the Local
4645 <primary>root superuser</primary>
4647 <secondary>limiting logins</secondary>
4652 <para>As in any computing environment, server machines must
4653 be located in a secured area. Any other security measures
4654 are effectively worthless if unauthorized people can access
4655 the computer hardware.</para>
4662 <title>System Administrators</title>
4667 <para>Limit the number of system administrators in your
4668 cell. Limit the use of system administrator accounts on
4669 publicly accessible workstations. Such machines are not
4670 secure, so unscrupulous users can install programs that try
4671 to steal tokens or passwords. If administrators must use
4672 publicly accessible workstations at times, they must issue
4673 the <emphasis role="bold">unlog</emphasis> command before
4674 leaving the machine.</para>
4678 <para>Create an administrative account for each
4679 administrator separate from the personal account, and assign
4680 AFS privileges only to the administrative account. The
4681 administrators must authenticate to the administrative
4682 accounts to perform duties that require privilege, which
4683 provides a useful audit trail as well.</para>
4687 <para>Administrators must not leave a machine unattended
4688 while they have valid tokens. Issue the <emphasis
4689 role="bold">unlog</emphasis> command before leaving.</para>
4693 <para>Use the <emphasis role="bold">-lifetime</emphasis>
4694 argument to the <emphasis role="bold">kas
4695 setfields</emphasis> command to set the token lifetime for
4696 administrative accounts to a fairly short amount of time.
4697 The default lifetime for AFS tokens is 25 hours, but 30 or
4698 60 minutes is possibly a more reasonable lifetime for
4699 administrative tokens. The tokens for administrators who
4700 initiate AFS Backup System operations must last somewhat
4701 longer, because it can take several hours to complete some
4702 dump operations, depending on the speed of the tape device
4703 and the network connecting it to the file server machines
4704 that house the volumes is it accessing.</para>
4708 <para>Limit administrators' use of the <emphasis
4709 role="bold">telnet</emphasis> program. It sends unencrypted
4710 passwords across the network. Similarly, limit use of other
4711 remote programs such as <emphasis role="bold">rsh</emphasis>
4712 and <emphasis role="bold">rcp</emphasis>, which send
4713 unencrypted tokens across the network.</para>
4720 <sect2 id="HDRWQ75">
4721 <title>A More Detailed Look at Mutual Authentication</title>
4724 <primary>mutual authentication</primary>
4728 <primary>distributed file system</primary>
4730 <secondary>security issues</secondary>
4734 <primary>shared secret</primary>
4738 <primary>server encryption key</primary>
4740 <secondary>defined</secondary>
4743 <para>As in any file system, security is a prime concern in AFS. A
4744 file system that makes file sharing easy is not useful if it makes
4745 file sharing mandatory, so AFS incorporates several features that
4746 prevent unauthorized users from accessing data. Security in a
4747 networked environment is difficult because almost all procedures
4748 require transmission of information across wires that almost anyone
4749 can tap into. Also, many machines on networks are powerful enough
4750 that unscrupulous users can monitor transactions or even intercept
4751 transmissions and fake the identity of one of the
4752 participants.</para>
4754 <para>The most effective precaution against eavesdropping and
4755 information theft or fakery is for servers and clients to accept the
4756 claimed identity of the other party only with sufficient proof. In
4757 other words, the nature of the network forces all parties on the
4758 network to assume that the other party in a transaction is not
4759 genuine until proven so. Mutual authentication is the means through
4760 which parties prove their genuineness.</para>
4762 <para>Because the measures needed to prevent fakery must be quite
4763 sophisticated, the implementation of mutual authentication
4764 procedures is complex. The underlying concept is simple, however:
4765 parties prove their identities by demonstrating knowledge of a
4766 shared secret. A shared secret is a piece of information known only
4767 to the parties who are mutually authenticating (they can sometimes
4768 learn it in the first place from a trusted third party or some other
4769 source). The party who originates the transaction presents the
4770 shared secret and refuses to accept the other party as valid until
4771 it shows that it knows the secret too.</para>
4773 <para>The most common form of shared secret in AFS transactions is
4774 the encryption key, also referred to simply as a key. The two
4775 parties use their shared key to encrypt the packets of information
4776 they send and to decrypt the ones they receive. Encryption using
4777 keys actually serves two related purposes. First, it protects
4778 messages as they cross the network, preventing anyone who does not
4779 know the key from eavesdropping. Second, ability to encrypt and
4780 decrypt messages successfully indicates that the parties are using
4781 the key (it is their shared secret). If they are using different
4782 keys, messages remain scrambled and unintelligible after
4785 <para>The following sections describe AFS's mutual authentication
4786 procedures in more detail. Feel free to skip these sections if you
4787 are not interested in the mutual authentication process.</para>
4789 <sect3 id="Header_92">
4790 <title>Simple Mutual Authentication</title>
4792 <para>Simple mutual authentication involves only one encryption
4793 key and two parties, generally a client and server. The client
4794 contacts the server by sending a challenge message encrypted with
4795 a key known only to the two of them. The server decrypts the
4796 message using its key, which is the same as the client's if they
4797 really do share the same secret. The server responds to the
4798 challenge and uses its key to encrypt its response. The client
4799 uses its key to decrypt the server's response, and if it is
4800 correct, then the client can be sure that the server is genuine:
4801 only someone who knows the same key as the client can decrypt the
4802 challenge and answer it correctly. On its side, the server
4803 concludes that the client is genuine because the challenge message
4804 made sense when the server decrypted it.</para>
4806 <para>AFS uses simple mutual authentication to verify user
4807 identities during the first part of the login procedure. In that
4808 case, the key is based on the user's password.</para>
4811 <sect3 id="HDRWQ76">
4812 <title>Complex Mutual Authentication</title>
4814 <para>Complex mutual authentication involves three encryption keys
4815 and three parties. All secure AFS transactions (except the first
4816 part of the login process) employ complex mutual
4817 authentication.</para>
4820 <primary>ticket-granter</primary>
4824 <primary>server encryption key</primary>
4828 <primary>tokens</primary>
4830 <secondary>data in</secondary>
4833 <para>When a client wishes to communicate with a server, it first
4834 contacts a third party called a ticket-granter. The ticket-granter
4835 and the client mutually authenticate using the simple
4836 procedure. When they finish, the ticket-granter gives the client a
4837 server ticket (or simply ticket) as proof that it (the
4838 ticket-granter) has preverified the identity of the client. The
4839 ticket-granter encrypts the ticket with the first of the three
4840 keys, called the server encryption key because it is known only to
4841 the ticket-granter and the server the client wants to contact. The
4842 client does not know this key.</para>
4844 <para>The ticket-granter sends several other pieces of information
4845 along with the ticket. They enable the client to use the ticket
4846 effectively despite being unable to decrypt the ticket
4847 itself. Along with the ticket, the items constitute a token:
4850 <para>A session key, which is the second encryption key
4851 involved in mutual authentication. The ticket-granter
4852 invents the session key at random as the shared secret
4853 between client and server. For reasons explained further
4854 below, the ticket-granter also puts a copy of the session
4855 key inside the ticket. The client and server use the session
4856 key to encrypt messages they send to one another during
4857 their transactions. The ticket-granter invents a different
4858 session key for each connection between a client and a
4859 server (there can be several transactions during a single
4863 <primary>session key</primary>
4868 <para>The name of the server for which the ticket is valid
4869 (and so which server encryption key encrypts the ticket
4874 <para>A ticket lifetime indicator. The default lifetime of
4875 AFS server tickets is 100 hours. If the client wants to
4876 contact the server again after the ticket expires, it must
4877 contact the ticket-granter to get a new ticket.</para>
4882 <para>The ticket-granter seals the entire token with the third key
4883 involved in complex mutual authentication--the key known only to
4884 it (the ticket-granter) and the client. In some cases, this third
4885 key is derived from the password of the human user whom the client
4888 <para>Now that the client has a valid server ticket, it is ready
4889 to contact the server. It sends the server two things:
4892 <para>The server ticket. This is encrypted with the server
4893 encryption key.</para>
4897 <para>Its request message, encrypted with the session
4898 key. Encrypting the message protects it as it crosses the
4899 network, since only the server/client pair for whom the
4900 ticket-granter invented the session key know it.</para>
4905 <para>At this point, the server does not know the session key,
4906 because the ticket-granter just created it. However, the
4907 ticket-granter put a copy of the session key inside the
4908 ticket. The server uses the server encryption key to decrypts the
4909 ticket and learns the session key. It then uses the session key to
4910 decrypt the client's request message. It generates a response and
4911 sends it to the client. It encrypts the response with the session
4912 key to protect it as it crosses the network.</para>
4914 <para>This step is the heart of mutual authentication between
4915 client and server, because it proves to both parties that they
4916 know the same secret:
4919 <para>The server concludes that the client is authorized to
4920 make a request because the request message makes sense when
4921 the server decrypts it using the session key. If the client
4922 uses a different session key than the one the server finds
4923 inside the ticket, then the request message remains
4924 unintelligible even after decryption. The two copies of the
4925 session key (the one inside the ticket and the one the
4926 client used) can only be the same if they both came from the
4927 ticket-granter. The client cannot fake knowledge of the
4928 session key because it cannot look inside the ticket, sealed
4929 as it is with the server encryption key known only to the
4930 server and the ticket-granter. The server trusts the
4931 ticket-granter to give tokens only to clients with whom it
4932 (the ticket-granter) has authenticated, so the server
4933 decides the client is legitimate.</para>
4935 <para>(Note that there is no direct communication between
4936 the ticket-granter and the server, even though their
4937 relationship is central to ticket-based mutual
4938 authentication. They interact only indirectly, via the
4939 client's possession of a ticket sealed with their shared
4944 <para>The client concludes that the server is genuine and
4945 trusts the response it gets back from the server, because
4946 the response makes sense after the client decrypts it using
4947 the session key. This indicates that the server encrypted
4948 the response with the same session key as the client
4949 knows. The only way for the server to learn that matching
4950 session key is to decrypt the ticket first. The server can
4951 only decrypt the ticket because it shares the secret of the
4952 server encryption key with the ticket-granter. The client
4953 trusts the ticket-granter to give out tickets only for
4954 legitimate servers, so the client accepts a server that can
4955 decrypt the ticket as genuine, and accepts its
4964 <sect1 id="HDRWQ77">
4965 <title>Backing Up AFS Data</title>
4967 <para>AFS provides two related facilities that help the administrator
4968 back up AFS data: backup volumes and the AFS Backup System.</para>
4970 <sect2 id="Header_95">
4971 <title>Backup Volumes</title>
4973 <para>The first facility is the backup volume, which you create by
4974 cloning a read/write volume. The backup volume is read-only and so
4975 preserves the state of the read/write volume at the time the clone
4978 <para>Backup volumes can ease administration if you mount them in
4979 the file system and make their contents available to users. For
4980 example, it often makes sense to mount the backup version of each
4981 user volume as a subdirectory of the user's home directory. A
4982 conventional name for this mount point is <emphasis
4983 role="bold">OldFiles</emphasis>. Create a new version of the backup
4984 volume (that is, reclone the read/write) once a day to capture any
4985 changes that were made since the previous backup. If a user
4986 accidentally removes or changes data, the user can restore it from
4987 the backup volume, rather than having to ask you to restore
4990 <para>The OpenAFS User Guide does not mention backup volumes, so
4991 regular users do not know about them if you decide not to use
4992 them. This implies that if you <emphasis role="bold">do</emphasis>
4993 make backup versions of user volumes, you need to tell your users
4994 about how the backup works and where you have mounted it.</para>
4996 <para>Users are often concerned that the data in a backup volume
4997 counts against their volume quota and some of them even want to
4998 remove the <emphasis role="bold">OldFiles</emphasis> mount point. It
4999 does not, because the backup volume is a separate volume. The only
5000 amount of space it uses in the user's volume is the amount needed
5001 for the mount point, which is about the same as the amount needed
5002 for a standard directory element.</para>
5004 <para>Backup volumes are discussed in detail in <link
5005 linkend="HDRWQ201">Creating Backup Volumes</link>.</para>
5008 <sect2 id="Header_96">
5009 <title>The AFS Backup System</title>
5011 <para>Backup volumes can reduce restoration requests, but they
5012 reside on disk and so do not protect data from loss due to hardware
5013 failure. Like any file system, AFS is vulnerable to this sort of
5016 <para>To protect your cell's users from permanent loss of data, you
5017 are strongly urged to back up your file system to tape on a regular
5018 and frequent schedule. The AFS Backup System is available to ease
5019 the administration and performance of backups. For detailed
5020 information about the AFS Backup System, see <link
5021 linkend="HDRWQ248">Configuring the AFS Backup System</link> and
5022 <link linkend="HDRWQ283">Backing Up and Restoring AFS
5027 <sect1 id="HDRWQ79">
5028 <title>Accessing AFS through NFS</title>
5030 <para>Users of NFS client machines can access the AFS filespace by
5031 mounting the <emphasis role="bold">/afs</emphasis> directory of an AFS
5032 client machine that is running the NFS/AFS Translator. This is a
5033 particular advantage in cells already running NFS who want to access
5034 AFS using client machines for which AFS is not available. See <link
5035 linkend="HDRWQ595">Appendix A, Managing the NFS/AFS
5036 Translator</link>.</para>
git://git.openafs.org / openafs.git / blob