<?xml version="1.0" encoding="UTF-8"?>
+
<chapter id="HDRWQ5">
<title>An Overview of OpenAFS Administration</title>
- <para>This chapter provides a broad overview of the concepts and organization of AFS. It is strongly recommended that anyone
- involved in administering an AFS cell read this chapter before beginning to issue commands.</para>
+ <para>This chapter provides a broad overview of the concepts and
+ organization of AFS. It is strongly recommended that anyone involved in
+ administering an AFS cell read this chapter before beginning to issue
+ commands.</para>
<sect1 id="HDRWQ6">
<title>A Broad Overview of AFS</title>
- <para>This section introduces most of the key terms and concepts necessary for a basic understanding of AFS. For a more detailed
- discussion, see <link linkend="HDRWQ7">More Detailed Discussions of Some Basic Concepts</link>.</para>
+ <para>This section introduces most of the key terms and concepts
+ necessary for a basic understanding of AFS. For a more detailed
+ discussion, see <link linkend="HDRWQ7">More Detailed Discussions of
+ Some Basic Concepts</link>.</para>
<sect2 renderas="sect3">
<title>AFS: A Distributed File System</title>
- <para>AFS is a distributed file system that enables users to share and access all of the files stored in a network of
- computers as easily as they access the files stored on their local machines. The file system is called distributed for this
- exact reason: files can reside on many different machines (be distributed across them), but are available to users on every
- machine.</para>
+ <para>AFS is a distributed file system that enables users to share
+ and access all of the files stored in a network of computers as
+ easily as they access the files stored on their local machines. The
+ file system is called distributed for this exact reason: files can
+ reside on many different machines (be distributed across them), but
+ are available to users on every machine.</para>
</sect2>
<sect2 renderas="sect3">
<title>Servers and Clients</title>
- <para>In fact, AFS stores files on a subset of the machines in a network, called file server machines. File server machines
- provide file storage and delivery service, along with other specialized services, to the other subset of machines in the
- network, the client machines. These machines are called clients because they make use of the servers' services while doing
- their own work. In a standard AFS configuration, clients provide computational power, access to the files in AFS and other
- "general purpose" tools to the users seated at their consoles. There are generally many more client workstations than file
- server machines.</para>
-
- <para>AFS file server machines run a number of server processes, so called because each provides a distinct specialized
- service: one handles file requests, another tracks file location, a third manages security, and so on. To avoid confusion, AFS
- documentation always refers to server machines and server processes, not simply to servers. For a more detailed description of
- the server processes, see <link linkend="HDRWQ17">AFS Server Processes and the Cache Manager</link>.</para>
+ <para>In fact, AFS stores files on a subset of the machines in a
+ network, called file server machines. File server machines provide
+ file storage and delivery service, along with other specialized
+ services, to the other subset of machines in the network, the client
+ machines. These machines are called clients because they make use of
+ the servers' services while doing their own work. In a standard AFS
+ configuration, clients provide computational power, access to the
+ files in AFS and other "general purpose" tools to the users seated
+ at their consoles. There are generally many more client workstations
+ than file server machines.</para>
+
+ <para>AFS file server machines run a number of server processes, so
+ called because each provides a distinct specialized service: one
+ handles file requests, another tracks file location, a third manages
+ security, and so on. To avoid confusion, AFS documentation always
+ refers to server machines and server processes, not simply to
+ servers. For a more detailed description of the server processes,
+ see <link linkend="HDRWQ17">AFS Server Processes and the Cache
+ Manager</link>.</para>
</sect2>
<sect2 renderas="sect3">
<title>Cells</title>
- <para>A cell is an administratively independent site running AFS. As a cell's system administrator, you make many decisions
- about configuring and maintaining your cell in the way that best serves its users, without having to consult the
- administrators in other cells. For example, you determine how many clients and servers to have, where to put files, and how to
- allocate client machines to users.</para>
+ <para>A cell is an administratively independent site running AFS. As
+ a cell's system administrator, you make many decisions about
+ configuring and maintaining your cell in the way that best serves
+ its users, without having to consult the administrators in other
+ cells. For example, you determine how many clients and servers to
+ have, where to put files, and how to allocate client machines to
+ users.</para>
</sect2>
<sect2 renderas="sect3">
<title>Transparent Access and the Uniform Namespace</title>
- <para>Although your AFS cell is administratively independent, you probably want to organize the local collection of files
- (your filespace or tree) so that users from other cells can also access the information in it. AFS enables cells to combine
- their local filespaces into a global filespace, and does so in such a way that file access is transparent--users do not need
- to know anything about a file's location in order to access it. All they need to know is the pathname of the file, which looks
- the same in every cell. Thus every user at every machine sees the collection of files in the same way, meaning that AFS
- provides a uniform namespace to its users.</para>
+ <para>Although your AFS cell is administratively independent, you
+ probably want to organize the local collection of files (your
+ filespace or tree) so that users from other cells can also access
+ the information in it. AFS enables cells to combine their local
+ filespaces into a global filespace, and does so in such a way that
+ file access is transparent--users do not need to know anything about
+ a file's location in order to access it. All they need to know is
+ the pathname of the file, which looks the same in every cell. Thus
+ every user at every machine sees the collection of files in the same
+ way, meaning that AFS provides a uniform namespace to its
+ users.</para>
</sect2>
<sect2 renderas="sect3">
<title>Volumes</title>
- <para>AFS groups files into volumes, making it possible to distribute files across many machines and yet maintain a uniform
- namespace. A volume is a unit of disk space that functions like a container for a set of related files, keeping them all
- together on one partition. Volumes can vary in size, but are (by definition) smaller than a partition.</para>
-
- <para>Volumes are important to system administrators and users for several reasons. Their small size makes them easy to move
- from one partition to another, or even between machines. The system administrator can maintain maximum efficiency by moving
- volumes to keep the load balanced evenly. In addition, volumes correspond to directories in the filespace--most cells store
- the contents of each user home directory in a separate volume. Thus the complete contents of the directory move together when
- the volume moves, making it easy for AFS to keep track of where a file is at a certain time. Volume moves are recorded
- automatically, so users do not have to keep track of file locations.</para>
+ <para>AFS groups files into volumes, making it possible to
+ distribute files across many machines and yet maintain a uniform
+ namespace. A volume is a unit of disk space that functions like a
+ container for a set of related files, keeping them all together on
+ one partition. Volumes can vary in size, but are (by definition)
+ smaller than a partition.</para>
+
+ <para>Volumes are important to system administrators and users for
+ several reasons. Their small size makes them easy to move from one
+ partition to another, or even between machines. The system
+ administrator can maintain maximum efficiency by moving volumes to
+ keep the load balanced evenly. In addition, volumes correspond to
+ directories in the filespace--most cells store the contents of each
+ user home directory in a separate volume. Thus the complete contents
+ of the directory move together when the volume moves, making it easy
+ for AFS to keep track of where a file is at a certain time. Volume
+ moves are recorded automatically, so users do not have to keep track
+ of file locations.</para>
</sect2>
<sect2 renderas="sect3">
<title>Efficiency Boosters: Replication and Caching</title>
- <para>AFS incorporates special features on server machines and client machines that help make it efficient and
- reliable.</para>
-
- <para>On server machines, AFS enables administrators to replicate commonly-used volumes, such as those containing binaries for
- popular programs. Replication means putting an identical read-only copy (sometimes called a clone) of a volume on more than
- one file server machine. The failure of one file server machine housing the volume does not interrupt users' work, because the
- volume's contents are still available from other machines. Replication also means that one machine does not become
- overburdened with requests for files from a popular volume.</para>
-
- <para>On client machines, AFS uses caching to improve efficiency. When a user on a client workstation requests a file, the
- Cache Manager on the client sends a request for the data to the File Server process running on the proper file server machine.
- The user does not need to know which machine this is; the Cache Manager determines file location automatically. The Cache
- Manager receives the file from the File Server process and puts it into the cache, an area of the client machine's local disk
- or memory dedicated to temporary file storage. Caching improves efficiency because the client does not need to send a request
- across the network every time the user wants the same file. Network traffic is minimized, and subsequent access to the file is
- especially fast because the file is stored locally. AFS has a way of ensuring that the cached file stays up-to-date, called a
- callback.</para>
+ <para>AFS incorporates special features on server machines and
+ client machines that help make it efficient and reliable.</para>
+
+ <para>On server machines, AFS enables administrators to replicate
+ commonly-used volumes, such as those containing binaries for popular
+ programs. Replication means putting an identical read-only copy
+ (sometimes called a clone) of a volume on more than one file server
+ machine. The failure of one file server machine housing the volume
+ does not interrupt users' work, because the volume's contents are
+ still available from other machines. Replication also means that one
+ machine does not become overburdened with requests for files from a
+ popular volume.</para>
+
+ <para>On client machines, AFS uses caching to improve
+ efficiency. When a user on a client workstation requests a file, the
+ Cache Manager on the client sends a request for the data to the File
+ Server process running on the proper file server machine. The user
+ does not need to know which machine this is; the Cache Manager
+ determines file location automatically. The Cache Manager receives
+ the file from the File Server process and puts it into the cache, an
+ area of the client machine's local disk or memory dedicated to
+ temporary file storage. Caching improves efficiency because the
+ client does not need to send a request across the network every time
+ the user wants the same file. Network traffic is minimized, and
+ subsequent access to the file is especially fast because the file is
+ stored locally. AFS has a way of ensuring that the cached file stays
+ up-to-date, called a callback.</para>
</sect2>
<sect2 renderas="sect3">
- <title>Security: Mutual Authentication and Access Control Lists</title>
-
- <para>Even in a cell where file sharing is especially frequent and widespread, it is not desirable that every user have equal
- access to every file. One way AFS provides adequate security is by requiring that servers and clients prove their identities
- to one another before they exchange information. This procedure, called mutual authentication, requires that both server and
- client demonstrate knowledge of a "shared secret" (like a password) known only to the two of them. Mutual authentication
- guarantees that servers provide information only to authorized clients and that clients receive information only from
- legitimate servers.</para>
-
- <para>Users themselves control another aspect of AFS security, by determining who has access to the directories they own. For
- any directory a user owns, he or she can build an access control list (ACL) that grants or denies access to the contents of
- the directory. An access control list pairs specific users with specific types of access privileges. There are seven separate
- permissions and up to twenty different people or groups of people can appear on an access control list.</para>
-
- <para>For a more detailed description of AFS's mutual authentication procedure, see <link linkend="HDRWQ75">A More Detailed
- Look at Mutual Authentication</link>. For further discussion of ACLs, see <link linkend="HDRWQ562">Managing Access Control
+ <title>Security: Mutual Authentication and Access Control
+ Lists</title>
+
+ <para>Even in a cell where file sharing is especially frequent and
+ widespread, it is not desirable that every user have equal access to
+ every file. One way AFS provides adequate security is by requiring
+ that servers and clients prove their identities to one another
+ before they exchange information. This procedure, called mutual
+ authentication, requires that both server and client demonstrate
+ knowledge of a "shared secret" (like a password) known only to the
+ two of them. Mutual authentication guarantees that servers provide
+ information only to authorized clients and that clients receive
+ information only from legitimate servers.</para>
+
+ <para>Users themselves control another aspect of AFS security, by
+ determining who has access to the directories they own. For any
+ directory a user owns, he or she can build an access control list
+ (ACL) that grants or denies access to the contents of the
+ directory. An access control list pairs specific users with specific
+ types of access privileges. There are seven separate permissions and
+ up to twenty different people or groups of people can appear on an
+ access control list.</para>
+
+ <para>For a more detailed description of AFS's mutual authentication
+ procedure, see <link linkend="HDRWQ75">A More Detailed Look at
+ Mutual Authentication</link>. For further discussion of ACLs, see
+ <link linkend="HDRWQ562">Managing Access Control
Lists</link>.</para>
</sect2>
</sect1>
<sect1 id="HDRWQ7">
<title>More Detailed Discussions of Some Basic Concepts</title>
- <para>The previous section offered a brief overview of the many concepts that an AFS system administrator needs to understand.
- The following sections examine some important concepts in more detail. Although not all concepts are new to an experienced
- administrator, reading this section helps ensure a common understanding of term and concepts.</para>
+ <para>The previous section offered a brief overview of the many
+ concepts that an AFS system administrator needs to understand. The
+ following sections examine some important concepts in more
+ detail. Although not all concepts are new to an experienced
+ administrator, reading this section helps ensure a common
+ understanding of term and concepts.</para>
<sect2 id="HDRWQ8">
<title>Networks</title>
<secondary>defined</secondary>
</indexterm>
- <para>A <emphasis>network</emphasis> is a collection of interconnected computers able to communicate with each other and
+ <para>A <emphasis>network</emphasis> is a collection of
+ interconnected computers able to communicate with each other and
transfer information back and forth.</para>
- <para>A networked computing environment contrasts with two types of computing environments: <emphasis>mainframe</emphasis> and
- <emphasis>personal</emphasis>. <indexterm>
- <primary>network</primary>
+ <para>A networked computing environment contrasts with two types of
+ computing environments: <emphasis>mainframe</emphasis> and
+ <emphasis>personal</emphasis>.
+ <indexterm>
+ <primary>network</primary>
- <secondary>as computing environment</secondary>
- </indexterm> <indexterm>
- <primary>environment</primary>
+ <secondary>as computing environment</secondary>
+ </indexterm>
+ <indexterm>
+ <primary>environment</primary>
- <secondary>types compared</secondary>
- </indexterm> <itemizedlist>
+ <secondary>types compared</secondary>
+ </indexterm>
+ <itemizedlist>
<listitem>
- <para>A <emphasis>mainframe</emphasis> computing environment is the most traditional. It uses a single powerful computer
- (the mainframe) to do the majority of the work in the system, both file storage and computation. It serves many users,
- who access their files and issue commands to the mainframe via terminals, which generally have only enough computing
- power to accept input from a keyboard and to display data on the screen.</para>
+ <para>A <emphasis>mainframe</emphasis> computing environment
+ is the most traditional. It uses a single powerful computer
+ (the mainframe) to do the majority of the work in the system,
+ both file storage and computation. It serves many users, who
+ access their files and issue commands to the mainframe via
+ terminals, which generally have only enough computing power to
+ accept input from a keyboard and to display data on the
+ screen.</para>
<indexterm>
<primary>mainframe</primary>
</listitem>
<listitem>
- <para>A <emphasis>personal</emphasis> computing environment is a single small computer that serves one (or, at the most,
- a few) users. Like a mainframe computer, the single computer stores all the files and performs all computation. Like a
- terminal, the personal computer provides access to the computer through a keyboard and screen.</para>
+ <para>A <emphasis>personal</emphasis> computing environment is
+ a single small computer that serves one (or, at the most, a
+ few) users. Like a mainframe computer, the single computer
+ stores all the files and performs all computation. Like a
+ terminal, the personal computer provides access to the
+ computer through a keyboard and screen.</para>
<indexterm>
<primary>personal</primary>
<secondary>computing environment</secondary>
</indexterm>
</listitem>
- </itemizedlist></para>
-
- <para>A network can connect computers of any kind, but the typical network running AFS connects high-function personal
- workstations. Each workstation has some computing power and local disk space, usually more than a personal computer or
- terminal, but less than a mainframe. For more about the classes of machines used in an AFS environment, see <link
- linkend="HDRWQ10">Servers and Clients</link>.</para>
+ </itemizedlist>
+ </para>
+
+ <para>A network can connect computers of any kind, but the typical
+ network running AFS connects high-function personal
+ workstations. Each workstation has some computing power and local
+ disk space, usually more than a personal computer or terminal, but
+ less than a mainframe. For more about the classes of machines used
+ in an AFS environment, see <link linkend="HDRWQ10">Servers and
+ Clients</link>.</para>
</sect2>
<sect2 id="HDRWQ9">
<primary>distributed file system</primary>
</indexterm>
- <para>A <emphasis>file system</emphasis> is a collection of files and the facilities (programs and commands) that enable users
- to access the information in the files. All computing environments have file systems. In a mainframe environment, the file
- system consists of all the files on the mainframe's storage disks, whereas in a personal computing environment it consists of
- the files on the computer's local disk.</para>
-
- <para>Networked computing environments often use <emphasis>distributed file systems</emphasis> like AFS. A distributed file
- system takes advantage of the interconnected nature of the network by storing files on more than one computer in the network
- and making them accessible to all of them. In other words, the responsibility for file storage and delivery is "distributed"
- among multiple machines instead of relying on only one. Despite the distribution of responsibility, a distributed file system
- like AFS creates the illusion that there is a single filespace.</para>
+ <para>A <emphasis>file system</emphasis> is a collection of files
+ and the facilities (programs and commands) that enable users to
+ access the information in the files. All computing environments have
+ file systems. In a mainframe environment, the file system consists
+ of all the files on the mainframe's storage disks, whereas in a
+ personal computing environment it consists of the files on the
+ computer's local disk.</para>
+
+ <para>Networked computing environments often use
+ <emphasis>distributed file systems</emphasis> like AFS. A
+ distributed file system takes advantage of the interconnected nature
+ of the network by storing files on more than one computer in the
+ network and making them accessible to all of them. In other words,
+ the responsibility for file storage and delivery is "distributed"
+ among multiple machines instead of relying on only one. Despite the
+ distribution of responsibility, a distributed file system like AFS
+ creates the illusion that there is a single filespace.</para>
</sect2>
<sect2 id="HDRWQ10">
<secondary>definition</secondary>
</indexterm>
- <para>AFS uses a server/client model. In general, a server is a machine, or a process running on a machine, that provides
- specialized services to other machines. A client is a machine or process that makes use of a server's specialized service
- during the course of its own work, which is often of a more general nature than the server's. The functional distinction
- between clients and server is not always strict, however--a server can be considered the client of another server whose
- service it is using.</para>
+ <para>AFS uses a server/client model. In general, a server is a
+ machine, or a process running on a machine, that provides
+ specialized services to other machines. A client is a machine or
+ process that makes use of a server's specialized service during the
+ course of its own work, which is often of a more general nature than
+ the server's. The functional distinction between clients and server
+ is not always strict, however--a server can be considered the client
+ of another server whose service it is using.</para>
- <para>AFS divides the machines on a network into two basic classes, <emphasis>file server machines</emphasis> and
- <emphasis>client machines</emphasis>, and assigns different tasks and responsibilities to each.</para>
+ <para>AFS divides the machines on a network into two basic classes,
+ <emphasis>file server machines</emphasis> and <emphasis>client
+ machines</emphasis>, and assigns different tasks and
+ responsibilities to each.</para>
<formalpara>
<title>File Server Machines</title>
<tertiary>definition</tertiary>
</indexterm>
- <para><emphasis>File server machines</emphasis> store the files in the distributed file system, and a <emphasis>server
- process</emphasis> running on the file server machine delivers and receives files. AFS file server machines run a number of
- <emphasis>server processes</emphasis>. Each process has a special function, such as maintaining databases important to AFS
- administration, managing security or handling volumes. This modular design enables each server process to specialize in one
- area, and thus perform more efficiently. For a description of the function of each AFS server process, see <link
- linkend="HDRWQ17">AFS Server Processes and the Cache Manager</link>.</para>
+ <para><emphasis>File server machines</emphasis> store the files in
+ the distributed file system, and a <emphasis>server
+ process</emphasis> running on the file server machine delivers and
+ receives files. AFS file server machines run a number of
+ <emphasis>server processes</emphasis>. Each process has a special
+ function, such as maintaining databases important to AFS
+ administration, managing security or handling volumes. This
+ modular design enables each server process to specialize in one
+ area, and thus perform more efficiently. For a description of the
+ function of each AFS server process, see <link
+ linkend="HDRWQ17">AFS Server Processes and the Cache
+ Manager</link>.</para>
</formalpara>
- <para>Not all AFS server machines must run all of the server processes. Some processes run on only a few machines because the
- demand for their services is low. Other processes run on only one machine in order to act as a synchronization site. See <link
- linkend="HDRWQ90">The Four Roles for File Server Machines</link>.</para>
+ <para>Not all AFS server machines must run all of the server
+ processes. Some processes run on only a few machines because the
+ demand for their services is low. Other processes run on only one
+ machine in order to act as a synchronization site. See <link
+ linkend="HDRWQ90">The Four Roles for File Server
+ Machines</link>.</para>
<formalpara>
<title>Client Machines</title>
<tertiary>definition</tertiary>
</indexterm>
- <para>The other class of machines are the <emphasis>client machines</emphasis>, which generally work directly for users,
- providing computational power and other general purpose tools. Clients also provide users with access to the files stored on
- the file server machines. Clients do not run any special processes per se, but do use a modified kernel that enables them to
- communicate with the AFS server processes running on the file server machines and to cache files. This collection of kernel
- modifications is referred to as the Cache Manager; see <link linkend="HDRWQ28">The Cache Manager</link>. There are usually
- many more client machines in a cell than file server machines.</para>
+ <para>The other class of machines are the <emphasis>client
+ machines</emphasis>, which generally work directly for users,
+ providing computational power and other general purpose
+ tools. Clients also provide users with access to the files stored
+ on the file server machines. Clients do not run any special
+ processes per se, but do use a modified kernel that enables them
+ to communicate with the AFS server processes running on the file
+ server machines and to cache files. This collection of kernel
+ modifications is referred to as the Cache Manager; see <link
+ linkend="HDRWQ28">The Cache Manager</link>. There are usually many
+ more client machines in a cell than file server machines.</para>
</formalpara>
<formalpara>
<tertiary>as typical AFS machine</tertiary>
</indexterm>
- <para>In the most typical AFS configuration, both file server machines and client machines are high-function workstations
- with disk drives. While this configuration is not required, it does have some advantages.</para>
+ <para>In the most typical AFS configuration, both file server
+ machines and client machines are high-function workstations with
+ disk drives. While this configuration is not required, it does
+ have some advantages.</para>
</formalpara>
- <para>There are several advantages to using personal workstations as file server machines. One is that it is easy to expand
- the network by adding another file server machine. It is also easy to increase storage space by adding disks to existing
- machines. Using workstations rather than more powerful mainframes makes it more economical to use multiple file server
- machines rather than one. Multiple file server machines provide an increase in system availability and reliability if popular
- files are available on more than one machine.</para>
-
- <para>The advantage of using workstations as clients is that caching on the local disk speeds the delivery of files to
- application programs. (For an explanation of caching, see <link linkend="HDRWQ16">Caching and Callbacks</link>.) Diskless
- machines can access AFS if they are running NFS(R) and the NFS/AFS Translator, an optional component of the AFS
- distribution.</para>
+ <para>There are several advantages to using personal workstations as
+ file server machines. One is that it is easy to expand the network
+ by adding another file server machine. It is also easy to increase
+ storage space by adding disks to existing machines. Using
+ workstations rather than more powerful mainframes makes it more
+ economical to use multiple file server machines rather than
+ one. Multiple file server machines provide an increase in system
+ availability and reliability if popular files are available on more
+ than one machine.</para>
+
+ <para>The advantage of using workstations as clients is that caching
+ on the local disk speeds the delivery of files to application
+ programs. (For an explanation of caching, see <link
+ linkend="HDRWQ16">Caching and Callbacks</link>.) Diskless machines
+ can access AFS if they are running NFS(R) and the NFS/AFS
+ Translator, an optional component of the AFS distribution.</para>
</sect2>
<sect2 id="HDRWQ11">
<primary>cell</primary>
</indexterm>
- <para>A <emphasis>cell</emphasis> is an independently administered site running AFS. In terms of hardware, it consists of a
- collection of file server machines and client machines defined as belonging to the cell; a machine can only belong to one cell
- at a time. Users also belong to a cell in the sense of having an account in it, but unlike machines can belong to (have an
- account in) multiple cells. To say that a cell is administratively independent means that its administrators determine many
- details of its configuration without having to consult administrators in other cells or a central authority. For example, a
- cell administrator determines how many machines of different types to run, where to put files in the local tree, how to
- associate volumes and directories, and how much space to allocate to each user.</para>
-
- <para>The terms <emphasis>local cell</emphasis> and <emphasis>home cell</emphasis> are equivalent, and refer to the cell in
- which a user has initially authenticated during a session, by logging onto a machine that belongs to that cell. All other
- cells are referred to as <emphasis>foreign</emphasis> from the user's perspective. In other words, throughout a login session,
- a user is accessing the filespace through a single Cache Manager--the one on the machine to which he or she initially logged
- in--whose cell membership defines the local cell. All other cells are considered foreign during that login session, even if
- the user authenticates in additional cells or uses the <emphasis role="bold">cd</emphasis> command to change directories into
- their file trees.</para>
+ <para>A <emphasis>cell</emphasis> is an independently administered
+ site running AFS. In terms of hardware, it consists of a collection
+ of file server machines and client machines defined as belonging to
+ the cell; a machine can only belong to one cell at a time. Users
+ also belong to a cell in the sense of having an account in it, but
+ unlike machines can belong to (have an account in) multiple
+ cells. To say that a cell is administratively independent means that
+ its administrators determine many details of its configuration
+ without having to consult administrators in other cells or a central
+ authority. For example, a cell administrator determines how many
+ machines of different types to run, where to put files in the local
+ tree, how to associate volumes and directories, and how much space
+ to allocate to each user.</para>
+
+ <para>The terms <emphasis>local cell</emphasis> and <emphasis>home
+ cell</emphasis> are equivalent, and refer to the cell in which a
+ user has initially authenticated during a session, by logging onto a
+ machine that belongs to that cell. All other cells are referred to
+ as <emphasis>foreign</emphasis> from the user's perspective. In
+ other words, throughout a login session, a user is accessing the
+ filespace through a single Cache Manager--the one on the machine to
+ which he or she initially logged in--whose cell membership defines
+ the local cell. All other cells are considered foreign during that
+ login session, even if the user authenticates in additional cells or
+ uses the <emphasis role="bold">cd</emphasis> command to change
+ directories into their file trees.</para>
<indexterm>
<primary>local cell</primary>
<secondary>foreign</secondary>
</indexterm>
- <para>It is possible to maintain more than one cell at a single geographical location. For instance, separate departments on a
- university campus or in a corporation can choose to administer their own cells. It is also possible to have machines at
- geographically distant sites belong to the same cell; only limits on the speed of network communication determine how
- practical this is.</para>
-
- <para>Despite their independence, AFS cells generally agree to make their local filespace visible to other AFS cells, so that
- users in different cells can share files if they choose. If your cell is to participate in the "global" AFS namespace, it must
- comply with a few basic conventions governing how the local filespace is configured and how the addresses of certain file
- server machines are advertised to the outside world.</para>
+ <para>It is possible to maintain more than one cell at a single
+ geographical location. For instance, separate departments on a
+ university campus or in a corporation can choose to administer their
+ own cells. It is also possible to have machines at geographically
+ distant sites belong to the same cell; only limits on the speed of
+ network communication determine how practical this is.</para>
+
+ <para>Despite their independence, AFS cells generally agree to make
+ their local filespace visible to other AFS cells, so that users in
+ different cells can share files if they choose. If your cell is to
+ participate in the "global" AFS namespace, it must comply with a few
+ basic conventions governing how the local filespace is configured
+ and how the addresses of certain file server machines are advertised
+ to the outside world.</para>
</sect2>
<sect2 id="HDRWQ12">
<secondary>transparent (AFS feature)</secondary>
</indexterm>
- <para>One of the features that makes AFS easy to use is that it provides transparent access to the files in a cell's
- filespace. Users do not have to know which file server machine stores a file in order to access it; they simply provide the
- file's pathname, which AFS automatically translates into a machine location.</para>
-
- <para>In addition to transparent access, AFS also creates a <emphasis>uniform namespace</emphasis>--a file's pathname is
- identical regardless of which client machine the user is working on. The cell's file tree looks the same when viewed from any
- client because the cell's file server machines store all the files centrally and present them in an identical manner to all
+ <para>One of the features that makes AFS easy to use is that it
+ provides transparent access to the files in a cell's
+ filespace. Users do not have to know which file server machine
+ stores a file in order to access it; they simply provide the file's
+ pathname, which AFS automatically translates into a machine
+ location.</para>
+
+ <para>In addition to transparent access, AFS also creates a
+ <emphasis>uniform namespace</emphasis>--a file's pathname is
+ identical regardless of which client machine the user is working
+ on. The cell's file tree looks the same when viewed from any client
+ because the cell's file server machines store all the files
+ centrally and present them in an identical manner to all
clients.</para>
- <para>To enable the transparent access and the uniform namespace features, the system administrator must follow a few simple
- conventions in configuring client machines and file trees. For details, see <link linkend="HDRWQ39">Making Other Cells Visible
- in Your Cell</link>.</para>
+ <para>To enable the transparent access and the uniform namespace
+ features, the system administrator must follow a few simple
+ conventions in configuring client machines and file trees. For
+ details, see <link linkend="HDRWQ39">Making Other Cells Visible in
+ Your Cell</link>.</para>
</sect2>
<sect2 id="HDRWQ13">
<secondary>definition</secondary>
</indexterm>
- <para>A <emphasis>volume</emphasis> is a conceptual container for a set of related files that keeps them all together on one
- file server machine partition. Volumes can vary in size, but are (by definition) smaller than a partition. Volumes are the
- main administrative unit in AFS, and have several characteristics that make administrative tasks easier and help improve
- overall system performance. <itemizedlist>
+ <para>A <emphasis>volume</emphasis> is a conceptual container for a
+ set of related files that keeps them all together on one file server
+ machine partition. Volumes can vary in size, but are (by definition)
+ smaller than a partition. Volumes are the main administrative unit
+ in AFS, and have several characteristics that make administrative
+ tasks easier and help improve overall system
+ performance. <itemizedlist>
<listitem>
- <para>The relatively small size of volumes makes them easy to move from one partition to another, or even between
+ <para>The relatively small size of volumes makes them easy to
+ move from one partition to another, or even between
machines.</para>
</listitem>
<listitem>
- <para>You can maintain maximum system efficiency by moving volumes to keep the load balanced evenly among the different
- machines. If a partition becomes full, the small size of individual volumes makes it easy to find enough room on other
+ <para>You can maintain maximum system efficiency by moving
+ volumes to keep the load balanced evenly among the different
+ machines. If a partition becomes full, the small size of
+ individual volumes makes it easy to find enough room on other
machines for them.</para>
<indexterm>
</listitem>
<listitem>
- <para>Each volume corresponds logically to a directory in the file tree and keeps together, on a single partition, all
- the data that makes up the files in the directory. By maintaining (for example) a separate volume for each user's home
- directory, you keep all of the user's files together, but separate from those of other users. This is an administrative
- convenience that is impossible if the partition is the smallest unit of storage.</para>
+ <para>Each volume corresponds logically to a directory in the
+ file tree and keeps together, on a single partition, all the
+ data that makes up the files in the directory. By maintaining
+ (for example) a separate volume for each user's home
+ directory, you keep all of the user's files together, but
+ separate from those of other users. This is an administrative
+ convenience that is impossible if the partition is the
+ smallest unit of storage.</para>
<indexterm>
<primary>volume</primary>
</listitem>
<listitem>
- <para>The directory/volume correspondence also makes transparent file access possible, because it simplifies the process
- of file location. All files in a directory reside together in one volume and in order to find a file, a file server
- process need only know the name of the file's parent directory, information which is included in the file's pathname.
- AFS knows how to translate the directory name into a volume name, and automatically tracks every volume's location, even
- when a volume is moved from machine to machine. For more about the directory/volume correspondence, see <link
- linkend="HDRWQ14">Mount Points</link>.</para>
+ <para>The directory/volume correspondence also makes
+ transparent file access possible, because it simplifies the
+ process of file location. All files in a directory reside
+ together in one volume and in order to find a file, a file
+ server process need only know the name of the file's parent
+ directory, information which is included in the file's
+ pathname. AFS knows how to translate the directory name into
+ a volume name, and automatically tracks every volume's
+ location, even when a volume is moved from machine to
+ machine. For more about the directory/volume correspondence,
+ see <link linkend="HDRWQ14">Mount Points</link>.</para>
</listitem>
<listitem>
- <para>Volumes increase file availability through replication and backup.</para>
+ <para>Volumes increase file availability through replication
+ and backup.</para>
<indexterm>
<primary>volume</primary>
</listitem>
<listitem>
- <para>Replication (placing copies of a volume on more than one file server machine) makes the contents more reliably
- available; for details, see <link linkend="HDRWQ15">Replication</link>. Entire sets of volumes can be backed up to tape
- and restored to the file system; see <link linkend="HDRWQ248">Configuring the AFS Backup System</link> and <link
- linkend="HDRWQ283">Backing Up and Restoring AFS Data</link>. In AFS, backup also refers to recording the state of a
- volume at a certain time and then storing it (either on tape or elsewhere in the file system) for recovery in the event
- files in it are accidentally deleted or changed. See <link linkend="HDRWQ201">Creating Backup Volumes</link>.</para>
+ <para>Replication (placing copies of a volume on more than one
+ file server machine) makes the contents more reliably
+ available; for details, see <link
+ linkend="HDRWQ15">Replication</link>. Entire sets of volumes
+ can be backed up to tape and restored to the file system; see
+ <link linkend="HDRWQ248">Configuring the AFS Backup
+ System</link> and <link linkend="HDRWQ283">Backing Up and
+ Restoring AFS Data</link>. In AFS, backup also refers to
+ recording the state of a volume at a certain time and then
+ storing it (either on tape or elsewhere in the file system)
+ for recovery in the event files in it are accidentally deleted
+ or changed. See <link linkend="HDRWQ201">Creating Backup
+ Volumes</link>.</para>
</listitem>
<listitem>
- <para>Volumes are the unit of resource management. A space quota associated with each volume sets a limit on the maximum
- volume size. See <link linkend="HDRWQ234">Setting and Displaying Volume Quota and Current Size</link>.</para>
+ <para>Volumes are the unit of resource management. A space
+ quota associated with each volume sets a limit on the maximum
+ volume size. See <link linkend="HDRWQ234">Setting and
+ Displaying Volume Quota and Current Size</link>.</para>
<indexterm>
<primary>volume</primary>
<tertiary>resource management</tertiary>
</indexterm>
</listitem>
- </itemizedlist></para>
+ </itemizedlist>
+ </para>
</sect2>
<sect2 id="HDRWQ14">
<secondary>definition</secondary>
</indexterm>
- <para>The previous section discussed how each volume corresponds logically to a directory in the file system: the volume keeps
- together on one partition all the data in the files residing in the directory. The directory that corresponds to a volume is
- called its <emphasis>root directory</emphasis>, and the mechanism that associates the directory and volume is called a
- <emphasis>mount point</emphasis>. A mount point is similar to a symbolic link in the file tree that specifies which volume
- contains the files kept in a directory. A mount point is not an actual symbolic link; its internal structure is
- different.</para>
+ <para>The previous section discussed how each volume corresponds
+ logically to a directory in the file system: the volume keeps
+ together on one partition all the data in the files residing in the
+ directory. The directory that corresponds to a volume is called its
+ <emphasis>root directory</emphasis>, and the mechanism that
+ associates the directory and volume is called a <emphasis>mount
+ point</emphasis>. A mount point is similar to a symbolic link in the
+ file tree that specifies which volume contains the files kept in a
+ directory. A mount point is not an actual symbolic link; its
+ internal structure is different.</para>
<note>
- <para>You must not create a symbolic link to a file whose name begins with the number sign (#) or the percent sign (%),
- because the Cache Manager interprets such a link as a mount point to a regular or read/write volume, respectively.</para>
+ <para>You must not create a symbolic link to a file whose name
+ begins with the number sign (#) or the percent sign (%), because
+ the Cache Manager interprets such a link as a mount point to a
+ regular or read/write volume, respectively.</para>
</note>
<indexterm>
<secondary>mounting</secondary>
</indexterm>
- <para>The use of mount points means that many of the elements in an AFS file tree that look and function just like standard
- UNIX file system directories are actually mount points. In form, a mount point is a one-line file that names the volume
- containing the data for files in the directory. When the Cache Manager (see <link linkend="HDRWQ28">The Cache Manager</link>)
- encounters a mount point--for example, in the course of interpreting a pathname--it looks in the volume named in the mount
- point. In the volume the Cache Manager finds an actual UNIX-style directory element--the volume's root directory--that lists
- the files contained in the directory/volume. The next element in the pathname appears in that list.</para>
-
- <para>A volume is said to be <emphasis>mounted</emphasis> at the point in the file tree where there is a mount point pointing
- to the volume. A volume's contents are not visible or accessible unless it is mounted.</para>
+ <para>The use of mount points means that many of the elements in an
+ AFS file tree that look and function just like standard UNIX file
+ system directories are actually mount points. In form, a mount point
+ is a one-line file that names the volume containing the data for
+ files in the directory. When the Cache Manager (see <link
+ linkend="HDRWQ28">The Cache Manager</link>) encounters a mount
+ point--for example, in the course of interpreting a pathname--it
+ looks in the volume named in the mount point. In the volume the
+ Cache Manager finds an actual UNIX-style directory element--the
+ volume's root directory--that lists the files contained in the
+ directory/volume. The next element in the pathname appears in that
+ list.</para>
+
+ <para>A volume is said to be <emphasis>mounted</emphasis> at the
+ point in the file tree where there is a mount point pointing to the
+ volume. A volume's contents are not visible or accessible unless it
+ is mounted.</para>
</sect2>
<sect2 id="HDRWQ15">
<primary>clone</primary>
</indexterm>
- <para><emphasis>Replication</emphasis> refers to making a copy, or <emphasis>clone</emphasis>, of a source read/write volume
- and then placing the copy on one or more additional file server machines in a cell. One benefit of replicating a volume is
- that it increases the availability of the contents. If one file server machine housing the volume fails, users can still
- access the volume on a different machine. No one machine need become overburdened with requests for a popular file, either,
- because the file is available from several machines.</para>
-
- <para>Replication is not necessarily appropriate for cells with limited disk space, nor are all types of volumes equally
- suitable for replication (replication is most appropriate for volumes that contain popular files that do not change very
- often). For more details, see <link linkend="HDRWQ50">When to Replicate Volumes</link>.</para>
+ <para><emphasis>Replication</emphasis> refers to making a copy, or
+ <emphasis>clone</emphasis>, of a source read/write volume and then
+ placing the copy on one or more additional file server machines in a
+ cell. One benefit of replicating a volume is that it increases the
+ availability of the contents. If one file server machine housing the
+ volume fails, users can still access the volume on a different
+ machine. No one machine need become overburdened with requests for a
+ popular file, either, because the file is available from several
+ machines.</para>
+
+ <para>Replication is not necessarily appropriate for cells with
+ limited disk space, nor are all types of volumes equally suitable
+ for replication (replication is most appropriate for volumes that
+ contain popular files that do not change very often). For more
+ details, see <link linkend="HDRWQ50">When to Replicate
+ Volumes</link>.</para>
</sect2>
<sect2 id="HDRWQ16">
<primary>caching</primary>
</indexterm>
- <para>Just as replication increases system availability, <emphasis>caching</emphasis> increases the speed and efficiency of
- file access in AFS. Each AFS client machine dedicates a portion of its local disk or memory to a cache where it stores data
- temporarily. Whenever an application program (such as a text editor) running on a client machine requests data from an AFS
- file, the request passes through the Cache Manager. The Cache Manager is a portion of the client machine's kernel that
- translates file requests from local application programs into cross-network requests to the <emphasis>File Server
- process</emphasis> running on the file server machine storing the file. When the Cache Manager receives the requested data
- from the File Server, it stores it in the cache and then passes it on to the application program.</para>
-
- <para>Caching improves the speed of data delivery to application programs in the following ways:</para>
+ <para>Just as replication increases system availability,
+ <emphasis>caching</emphasis> increases the speed and efficiency of
+ file access in AFS. Each AFS client machine dedicates a portion of
+ its local disk or memory to a cache where it stores data
+ temporarily. Whenever an application program (such as a text editor)
+ running on a client machine requests data from an AFS file, the
+ request passes through the Cache Manager. The Cache Manager is a
+ portion of the client machine's kernel that translates file requests
+ from local application programs into cross-network requests to the
+ <emphasis>File Server process</emphasis> running on the file server
+ machine storing the file. When the Cache Manager receives the
+ requested data from the File Server, it stores it in the cache and
+ then passes it on to the application program.</para>
+
+ <para>Caching improves the speed of data delivery to application
+ programs in the following ways:</para>
<itemizedlist>
<listitem>
- <para>When the application program repeatedly asks for data from the same file, it is already on the local disk. The
- application does not have to wait for the Cache Manager to request and receive the data from the File Server.</para>
+ <para>When the application program repeatedly asks for data from
+ the same file, it is already on the local disk. The application
+ does not have to wait for the Cache Manager to request and
+ receive the data from the File Server.</para>
</listitem>
<listitem>
- <para>Caching data eliminates the need for repeated request and transfer of the same data, so network traffic is reduced.
- Thus, initial requests and other traffic can get through more quickly.</para>
+ <para>Caching data eliminates the need for repeated request and
+ transfer of the same data, so network traffic is reduced. Thus,
+ initial requests and other traffic can get through more
+ quickly.</para>
<indexterm>
<primary>AFS</primary>
<secondary>cached data</secondary>
</indexterm>
- <para>While caching provides many advantages, it also creates the problem of maintaining consistency among the many cached
- copies of a file and the source version of a file. This problem is solved using a mechanism referred to as a
- <emphasis>callback</emphasis>.</para>
+ <para>While caching provides many advantages, it also creates the
+ problem of maintaining consistency among the many cached copies of a
+ file and the source version of a file. This problem is solved using
+ a mechanism referred to as a <emphasis>callback</emphasis>.</para>
- <para>A callback is a promise by a File Server to a Cache Manager to inform the latter when a change is made to any of the
- data delivered by the File Server. Callbacks are used differently based on the type of file delivered by the File Server:
- <itemizedlist>
+ <para>A callback is a promise by a File Server to a Cache Manager to
+ inform the latter when a change is made to any of the data delivered
+ by the File Server. Callbacks are used differently based on the type
+ of file delivered by the File Server: <itemizedlist>
<listitem>
- <para>When a File Server delivers a writable copy of a file (from a read/write volume) to the Cache Manager, the File
- Server sends along a callback with that file. If the source version of the file is changed by another user, the File
- Server breaks the callback associated with the cached version of that file--indicating to the Cache Manager that it
- needs to update the cached copy.</para>
+ <para>When a File Server delivers a writable copy of a file
+ (from a read/write volume) to the Cache Manager, the File
+ Server sends along a callback with that file. If the source
+ version of the file is changed by another user, the File
+ Server breaks the callback associated with the cached version
+ of that file--indicating to the Cache Manager that it needs to
+ update the cached copy.</para>
</listitem>
<listitem>
- <para>When a File Server delivers a file from a read-only volume to the Cache Manager, the File Server sends along a
- callback associated with the entire volume (so it does not need to send any more callbacks when it delivers additional
- files from the volume). Only a single callback is required per accessed read-only volume because files in a read-only
- volume can change only when a new version of the complete volume is released. All callbacks associated with the old
- version of the volume are broken at release time.</para>
- </listitem>
- </itemizedlist></para>
-
- <para>The callback mechanism ensures that the Cache Manager always requests the most up-to-date version of a file. However, it
- does not ensure that the user necessarily notices the most current version as soon as the Cache Manager has it. That depends
- on how often the application program requests additional data from the File System or how often it checks with the Cache
- Manager.</para>
+ <para>When a File Server delivers a file from a read-only
+ volume to the Cache Manager, the File Server sends along a
+ callback associated with the entire volume (so it does not
+ need to send any more callbacks when it delivers additional
+ files from the volume). Only a single callback is required per
+ accessed read-only volume because files in a read-only volume
+ can change only when a new version of the complete volume is
+ released. All callbacks associated with the old version of the
+ volume are broken at release time.</para>
+ </listitem> </itemizedlist></para>
+
+ <para>The callback mechanism ensures that the Cache Manager always
+ requests the most up-to-date version of a file. However, it does not
+ ensure that the user necessarily notices the most current version as
+ soon as the Cache Manager has it. That depends on how often the
+ application program requests additional data from the File System or
+ how often it checks with the Cache Manager.</para>
</sect2>
</sect1>
<tertiary>list of AFS</tertiary>
</indexterm>
- <para>As mentioned in <link linkend="HDRWQ10">Servers and Clients</link>, AFS file server machines run a number of processes,
- each with a specialized function. One of the main responsibilities of a system administrator is to make sure that processes are
- running correctly as much of the time as possible, using the administrative services that the server processes provide.</para>
-
- <para>The following list briefly describes the function of each server process and the Cache Manager; the following sections
- then discuss the important features in more detail.</para>
-
- <para>The <emphasis>File Server</emphasis>, the most fundamental of the servers, delivers data files from the file server
- machine to local workstations as requested, and stores the files again when the user saves any changes to the files.</para>
-
- <para>The <emphasis>Basic OverSeer Server (BOS Server)</emphasis> ensures that the other server processes on its server machine
- are running correctly as much of the time as possible, since a server is useful only if it is available. The BOS Server relieves
- system administrators of much of the responsibility for overseeing system operations.</para>
-
- <para>The third-party <emphasis>Kerberos Server</emphasis> replaces the old <emphasis>Authentication Server</emphasis> and helps ensure that communications on the network are secure. It verifies
- user identities at login and provides the facilities through which participants in transactions prove their identities to one
- another (mutually authenticate).</para>
-
- <para>The Protection Server helps users control who has access to their files and directories. Users can grant access to several
- other users at once by putting them all in a group entry in the Protection Database maintained by the Protection Server.</para>
-
- <para>The <emphasis>Volume Server</emphasis> performs all types of volume manipulation. It helps the administrator move volumes
- from one server machine to another to balance the workload among the various machines.</para>
-
- <para>The <emphasis>Volume Location Server (VL Server)</emphasis> maintains the Volume Location Database (VLDB), in which it
- records the location of volumes as they move from file server machine to file server machine. This service is the key to
- transparent file access for users.</para>
-
- <para>The <emphasis>Update Server</emphasis> distributes new versions of AFS server process software and configuration
- information to all file server machines. It is crucial to stable system performance that all server machines run the same
- software.</para>
-
- <para>The <emphasis>Backup Server</emphasis> maintains the Backup Database, in which it stores information related to the Backup
- System. It enables the administrator to back up data from volumes to tape. The data can then be restored from tape in the event
- that it is lost from the file system.</para>
-
- <para>The <emphasis>Salvager</emphasis> is not a server in the sense that others are. It runs only after the File Server or
- Volume Server fails; it repairs any inconsistencies caused by the failure. The system administrator can invoke it directly if
- necessary.</para>
-
- <para>The <emphasis>Network Time Protocol Daemon (NTPD)</emphasis> is not an AFS server process per se, but plays a vital role
- nonetheless. It synchronizes the internal clock on a file server machine with those on other machines. Synchronized clocks are
- particularly important for correct functioning of the AFS distributed database technology (known as Ubik); see <link
- linkend="HDRWQ103">Configuring the Cell for Proper Ubik Operation</link>. The NTPD is usually provided with the operating system.</para>
-
- <para>The <emphasis>Cache Manager</emphasis> is the one component in this list that resides on AFS client rather than file
- server machines. It not a process per se, but rather a part of the kernel on AFS client machines that communicates with AFS
- server processes. Its main responsibilities are to retrieve files for application programs running on the client and to maintain
- the files in the cache.</para>
+ <para>As mentioned in <link linkend="HDRWQ10">Servers and
+ Clients</link>, AFS file server machines run a number of processes,
+ each with a specialized function. One of the main responsibilities of
+ a system administrator is to make sure that processes are running
+ correctly as much of the time as possible, using the administrative
+ services that the server processes provide.</para>
+
+ <para>The following list briefly describes the function of each server
+ process and the Cache Manager; the following sections then discuss the
+ important features in more detail.</para>
+
+ <para>The <emphasis>File Server</emphasis>, the most fundamental of
+ the servers, delivers data files from the file server machine to local
+ workstations as requested, and stores the files again when the user
+ saves any changes to the files.</para>
+
+ <para>The <emphasis>Basic OverSeer Server (BOS Server)</emphasis>
+ ensures that the other server processes on its server machine are
+ running correctly as much of the time as possible, since a server is
+ useful only if it is available. The BOS Server relieves system
+ administrators of much of the responsibility for overseeing system
+ operations.</para>
+
+ <para>The third-party <emphasis>Kerberos Server</emphasis> replaces
+ the old <emphasis>Authentication Server</emphasis> and helps ensure
+ that communications on the network are secure. It verifies user
+ identities at login and provides the facilities through which
+ participants in transactions prove their identities to one another
+ (mutually authenticate).</para>
+
+ <para>The Protection Server helps users control who has access to
+ their files and directories. Users can grant access to several other
+ users at once by putting them all in a group entry in the Protection
+ Database maintained by the Protection Server.</para>
+
+ <para>The <emphasis>Volume Server</emphasis> performs all types of
+ volume manipulation. It helps the administrator move volumes from one
+ server machine to another to balance the workload among the various
+ machines.</para>
+
+ <para>The <emphasis>Volume Location Server (VL Server)</emphasis>
+ maintains the Volume Location Database (VLDB), in which it records the
+ location of volumes as they move from file server machine to file
+ server machine. This service is the key to transparent file access for
+ users.</para>
+
+ <para>The <emphasis>Update Server</emphasis> distributes new versions
+ of AFS server process software and configuration information to all
+ file server machines. It is crucial to stable system performance that
+ all server machines run the same software.</para>
+
+ <para>The <emphasis>Backup Server</emphasis> maintains the Backup
+ Database, in which it stores information related to the Backup
+ System. It enables the administrator to back up data from volumes to
+ tape. The data can then be restored from tape in the event that it is
+ lost from the file system.</para>
+
+ <para>The <emphasis>Salvager</emphasis> is not a server in the sense
+ that others are. It runs only after the File Server or Volume Server
+ fails; it repairs any inconsistencies caused by the failure. The
+ system administrator can invoke it directly if necessary.</para>
+
+ <para>The <emphasis>Network Time Protocol Daemon (NTPD)</emphasis> is
+ not an AFS server process per se, but plays a vital role
+ nonetheless. It synchronizes the internal clock on a file server
+ machine with those on other machines. Synchronized clocks are
+ particularly important for correct functioning of the AFS distributed
+ database technology (known as Ubik); see <link
+ linkend="HDRWQ103">Configuring the Cell for Proper Ubik
+ Operation</link>. The NTPD is usually provided with the operating
+ system.</para>
+
+ <para>The <emphasis>Cache Manager</emphasis> is the one component in
+ this list that resides on AFS client rather than file server
+ machines. It not a process per se, but rather a part of the kernel on
+ AFS client machines that communicates with AFS server processes. Its
+ main responsibilities are to retrieve files for application programs
+ running on the client and to maintain the files in the cache.</para>
<sect2 id="HDRWQ18">
<title>The File Server</title>
<secondary>description</secondary>
</indexterm>
- <para>The <emphasis>File Server</emphasis> is the most fundamental of the AFS server processes and runs on each file server
- machine. It provides the same services across the network that the UNIX file system provides on the local disk: <itemizedlist>
+ <para>The <emphasis>File Server</emphasis> is the most fundamental
+ of the AFS server processes and runs on each file server machine. It
+ provides the same services across the network that the UNIX file
+ system provides on the local disk: <itemizedlist>
<listitem>
- <para>Delivering programs and data files to client workstations as requested and storing them again when the client
- workstation finishes with them.</para>
+ <para>Delivering programs and data files to client
+ workstations as requested and storing them again when the
+ client workstation finishes with them.</para>
</listitem>
<listitem>
- <para>Maintaining the hierarchical directory structure that users create to organize their files.</para>
- </listitem>
+ <para>Maintaining the hierarchical directory structure that
+ users create to organize their files.</para> </listitem>
<listitem>
- <para>Handling requests for copying, moving, creating, and deleting files and directories.</para>
- </listitem>
+ <para>Handling requests for copying, moving, creating, and
+ deleting files and directories.</para> </listitem>
<listitem>
- <para>Keeping track of status information about each file and directory (including its size and latest modification
+ <para>Keeping track of status information about each file and
+ directory (including its size and latest modification
time).</para>
</listitem>
<listitem>
- <para>Making sure that users are authorized to perform the actions they request on particular files or
+ <para>Making sure that users are authorized to perform the
+ actions they request on particular files or
directories.</para>
</listitem>
</listitem>
<listitem>
- <para>Granting advisory locks (corresponding to UNIX locks) on request.</para>
- </listitem>
- </itemizedlist></para>
+ <para>Granting advisory locks (corresponding to UNIX locks) on
+ request.</para> </listitem>
+ </itemizedlist>
+ </para>
</sect2>
<sect2 id="HDRWQ19">
<secondary>description</secondary>
</indexterm>
- <para>The <emphasis>Basic OverSeer Server (BOS Server)</emphasis> reduces the demands on system administrators by constantly
- monitoring the processes running on its file server machine. It can restart failed processes automatically and provides a
- convenient interface for administrative tasks.</para>
+ <para>The <emphasis>Basic OverSeer Server (BOS Server)</emphasis>
+ reduces the demands on system administrators by constantly
+ monitoring the processes running on its file server machine. It can
+ restart failed processes automatically and provides a convenient
+ interface for administrative tasks.</para>
- <para>The BOS Server runs on every file server machine. Its primary function is to minimize system outages. It also</para>
+ <para>The BOS Server runs on every file server machine. Its primary
+ function is to minimize system outages. It also</para>
<itemizedlist>
<listitem>
- <para>Constantly monitors the other server processes (on the local machine) to make sure they are running
- correctly.</para>
+ <para>Constantly monitors the other server processes (on the
+ local machine) to make sure they are running correctly.</para>
</listitem>
<listitem>
- <para>Automatically restarts failed processes, without contacting a human operator. When restarting multiple server
- processes simultaneously, the BOS server takes interdependencies into account and initiates restarts in the correct
- order.</para>
+ <para>Automatically restarts failed processes, without
+ contacting a human operator. When restarting multiple server
+ processes simultaneously, the BOS server takes interdependencies
+ into account and initiates restarts in the correct order.</para>
<indexterm>
<primary>system outages</primary>
</listitem>
<listitem>
- <para>Accepts requests from the system administrator. Common reasons to contact BOS are to verify the status of server
- processes on file server machines, install and start new processes, stop processes either temporarily or permanently, and
+ <para>Accepts requests from the system administrator. Common
+ reasons to contact BOS are to verify the status of server
+ processes on file server machines, install and start new
+ processes, stop processes either temporarily or permanently, and
restart dead processes manually.</para>
</listitem>
<listitem>
- <para>Helps system administrators to manage system configuration information. The BOS server automates the process of
- adding and changing <emphasis>server encryption keys</emphasis>, which are important in mutual authentication. The BOS
- Server also provides a simple interface for modifying two files that contain information about privileged users and
- certain special file server machines. For more details about these configuration files, see <link linkend="HDRWQ85">Common
- Configuration Files in the /usr/afs/etc Directory</link>.</para>
- </listitem>
- </itemizedlist>
+ <para>Helps system administrators to manage system configuration
+ information. The BOS server automates the process of adding and
+ changing <emphasis>server encryption keys</emphasis>, which are
+ important in mutual authentication. The BOS Server also provides
+ a simple interface for modifying two files that contain
+ information about privileged users and certain special file
+ server machines. For more details about these configuration
+ files, see <link linkend="HDRWQ85">Common Configuration Files in
+ the /usr/afs/etc Directory</link>.</para>
+ </listitem> </itemizedlist>
</sect2>
<sect2 id="HDRWQ20">
<indexterm>
<primary>Kerberos Server</primary>
-
<secondary>description</secondary>
</indexterm>
<indexterm>
<primary>Authentication Server</primary>
-
<secondary>description</secondary>
<seealso>Kerberos Server</seealso>
</indexterm>
<secondary>Kerberos Server</secondary>
</indexterm>
-
-
- <para>The <emphasis>Kerberos Server</emphasis> performs two main functions related to network security: <itemizedlist>
+ <para>The <emphasis>Kerberos Server</emphasis> performs two main
+ functions related to network security: <itemizedlist>
<listitem>
- <para>Verifying the identity of users as they log into the system by requiring that they provide a password. The
- Kerberos Server grants the user a ticket, which is converted into a token to prove to AFS server processes that the user has authenticated. For more
- on tokens, see <link linkend="HDRWQ76">Complex Mutual Authentication</link>.</para>
+ <para>Verifying the identity of users as they log into the
+ system by requiring that they provide a password. The Kerberos
+ Server grants the user a ticket, which is converted into a
+ token to prove to AFS server processes that the user has
+ authenticated. For more on tokens, see <link
+ linkend="HDRWQ76">Complex Mutual Authentication</link>.</para>
</listitem>
<listitem>
- <para>Providing the means through which server and client processes prove their identities to each other (mutually
- authenticate). This helps to create a secure environment in which to send cross-network messages.</para>
- </listitem>
- </itemizedlist></para>
+ <para>Providing the means through which server and client
+ processes prove their identities to each other (mutually
+ authenticate). This helps to create a secure environment in
+ which to send cross-network messages.</para>
+ </listitem> </itemizedlist></para>
<para>The Kerberos Server is a required service which is provided by
a third-party Kerberos server that supports version 5 of the
operating systems or may be acquired separately. MIT Kerberos,
Heimdal, and Microsoft Active Directory are known to work with
OpenAFS as a Kerberos Server. (Most Kerberos commands begin with
- the letter
- <emphasis role="bold">k</emphasis>). This technology was originally developed by the Massachusetts Institute of Technology's
+ the letter <emphasis role="bold">k</emphasis>). This technology was
+ originally developed by the Massachusetts Institute of Technology's
Project Athena.</para>
- <para>The Kerberos Server also maintains the <emphasis>Authentication Database</emphasis>, in which it stores user
- passwords converted into encryption key form as well as the AFS server encryption key. To learn more about the procedures AFS
- uses to verify user identity and during mutual authentication, see <link linkend="HDRWQ75">A More Detailed Look at Mutual
+ <para>The Kerberos Server also maintains the
+ <emphasis>Authentication Database</emphasis>, in which it stores
+ user passwords converted into encryption key form as well as the AFS
+ server encryption key. To learn more about the procedures AFS uses
+ to verify user identity and during mutual authentication, see <link
+ linkend="HDRWQ75">A More Detailed Look at Mutual
Authentication</link>.</para>
<note><para>The <emphasis>Authentication Server</emphasis> known as
the Kerberos Server. All references to the <emphasis>Kerberos
Server</emphasis> in this guide refer to a Kerberos 5
server.</para></note>
-
<indexterm>
<primary>AFS</primary>
<secondary>in UNIX</secondary>
</indexterm>
- <para>The <emphasis>Protection Server</emphasis> is the key to AFS's refinement of the normal UNIX methods for protecting
- files and directories from unauthorized use. The refinements include the following: <itemizedlist>
+ <para>The <emphasis>Protection Server</emphasis> is the key to AFS's
+ refinement of the normal UNIX methods for protecting files and
+ directories from unauthorized use. The refinements include the
+ following: <itemizedlist>
<listitem>
- <para>Defining seven access permissions rather than the standard UNIX file system's three. In conjunction with the UNIX
- mode bits associated with each file and directory element, AFS associates an <emphasis>access control list
- (ACL)</emphasis> with each directory. The ACL specifies which users have which of the seven specific permissions for the
- directory and all the files it contains. For a definition of AFS's seven access permissions and how users can set them
- on access control lists, see <link linkend="HDRWQ562">Managing Access Control Lists</link>.</para>
+ <para>Defining seven access permissions rather than the
+ standard UNIX file system's three. In conjunction with the
+ UNIX mode bits associated with each file and directory
+ element, AFS associates an <emphasis>access control list
+ (ACL)</emphasis> with each directory. The ACL specifies which
+ users have which of the seven specific permissions for the
+ directory and all the files it contains. For a definition of
+ AFS's seven access permissions and how users can set them on
+ access control lists, see <link linkend="HDRWQ562">Managing
+ Access Control Lists</link>.</para>
<indexterm>
<primary>access</primary>
</listitem>
<listitem>
- <para>Enabling users to grant permissions to numerous individual users--a different combination to each individual if
- desired. UNIX protection distinguishes only between three user or groups: the owner of the file, members of a single
- specified group, and everyone who can access the local file system.</para>
+ <para>Enabling users to grant permissions to numerous
+ individual users--a different combination to each individual
+ if desired. UNIX protection distinguishes only between three
+ user or groups: the owner of the file, members of a single
+ specified group, and everyone who can access the local file
+ system.</para>
</listitem>
<listitem>
- <para>Enabling users to define their own groups of users, recorded in the <emphasis>Protection Database</emphasis>
- maintained by the Protection Server. The groups then appear on directories' access control lists as though they were
- individuals, which enables the granting of permissions to many users simultaneously.</para>
+ <para>Enabling users to define their own groups of users,
+ recorded in the <emphasis>Protection Database</emphasis>
+ maintained by the Protection Server. The groups then appear on
+ directories' access control lists as though they were
+ individuals, which enables the granting of permissions to many
+ users simultaneously.</para>
</listitem>
<listitem>
- <para>Enabling system administrators to create groups containing client machine IP addresses to permit access when it
- originates from the specified client machines. These types of groups are useful when it is necessary to adhere to
+ <para>Enabling system administrators to create groups
+ containing client machine IP addresses to permit access when
+ it originates from the specified client machines. These types
+ of groups are useful when it is necessary to adhere to
machine-based licensing restrictions.</para>
</listitem>
- </itemizedlist></para>
+ </itemizedlist>
+ </para>
<indexterm>
<primary>group</primary>
<primary>Protection Database</primary>
</indexterm>
- <para>The Protection Server's main duty is to help the File Server determine if a user is authorized to access a file in the
- requested manner. The Protection Server creates a list of all the groups to which the user belongs. The File Server then
- compares this list to the ACL associated with the file's parent directory. A user thus acquires access both as an individual
- and as a member of any groups.</para>
-
- <para>The Protection Server also maps usernames (the name typed at the login prompt) to <emphasis>AFS user ID</emphasis>
- numbers (<emphasis>AFS UIDs</emphasis>). These UIDs are functionally equivalent to UNIX UIDs, but operate in the domain of AFS
- rather than in the UNIX file system on a machine's local disk. This conversion service is essential because the tokens that
- the Authentication Server grants to authenticated users are stamped with usernames (to comply with Kerberos standards). The
- AFS server processes identify users by AFS UID, not by username. Before they can understand whom the token represents, they
- need the Protection Server to translate the username into an AFS UID. For further discussion of tokens, see <link
- linkend="HDRWQ75">A More Detailed Look at Mutual Authentication</link>.</para>
+ <para>The Protection Server's main duty is to help the File Server
+ determine if a user is authorized to access a file in the requested
+ manner. The Protection Server creates a list of all the groups to
+ which the user belongs. The File Server then compares this list to
+ the ACL associated with the file's parent directory. A user thus
+ acquires access both as an individual and as a member of any
+ groups.</para>
+
+ <para>The Protection Server also maps usernames (the name typed at
+ the login prompt) to <emphasis>AFS user ID</emphasis> numbers
+ (<emphasis>AFS UIDs</emphasis>). These UIDs are functionally
+ equivalent to UNIX UIDs, but operate in the domain of AFS rather
+ than in the UNIX file system on a machine's local disk. This
+ conversion service is essential because the tokens that the
+ Authentication Server grants to authenticated users are stamped with
+ usernames (to comply with Kerberos standards). The AFS server
+ processes identify users by AFS UID, not by username. Before they
+ can understand whom the token represents, they need the Protection
+ Server to translate the username into an AFS UID. For further
+ discussion of tokens, see <link linkend="HDRWQ75">A More Detailed
+ Look at Mutual Authentication</link>.</para>
</sect2>
<sect2 id="HDRWQ22">
<secondary>description</secondary>
</indexterm>
- <para>The <emphasis>Volume Server</emphasis> provides the interface through which you create, delete, move, and replicate
- volumes, as well as prepare them for archiving to tape or other media (backing up). <link linkend="HDRWQ13">Volumes</link>
- explained the advantages gained by storing files in volumes. Creating and deleting volumes are necessary when adding and
- removing users from the system; volume moves are done for load balancing; and replication enables volume placement on multiple
- file server machines (for more on replication, see <link linkend="HDRWQ15">Replication</link>).</para>
+ <para>The <emphasis>Volume Server</emphasis> provides the interface
+ through which you create, delete, move, and replicate volumes, as
+ well as prepare them for archiving to tape or other media (backing
+ up). <link linkend="HDRWQ13">Volumes</link> explained the advantages
+ gained by storing files in volumes. Creating and deleting volumes
+ are necessary when adding and removing users from the system; volume
+ moves are done for load balancing; and replication enables volume
+ placement on multiple file server machines (for more on replication,
+ see <link linkend="HDRWQ15">Replication</link>).</para>
</sect2>
<sect2 id="HDRWQ23">
<primary>VLDB</primary>
</indexterm>
- <para>The <emphasis>VL Server</emphasis> maintains a complete list of volume locations in the <emphasis>Volume Location
- Database (VLDB)</emphasis>. When the Cache Manager (see <link linkend="HDRWQ28">The Cache Manager</link>) begins to fill a
- file request from an application program, it first contacts the VL Server in order to learn which file server machine
- currently houses the volume containing the file. The Cache Manager then requests the file from the File Server process running
- on that file server machine.</para>
+ <para>The <emphasis>VL Server</emphasis> maintains a complete list
+ of volume locations in the <emphasis>Volume Location Database
+ (VLDB)</emphasis>. When the Cache Manager (see <link
+ linkend="HDRWQ28">The Cache Manager</link>) begins to fill a file
+ request from an application program, it first contacts the VL Server
+ in order to learn which file server machine currently houses the
+ volume containing the file. The Cache Manager then requests the file
+ from the File Server process running on that file server
+ machine.</para>
- <para>The VLDB and VL Server make it possible for AFS to take advantage of the increased system availability gained by using
- multiple file server machines, because the Cache Manager knows where to find a particular file. Indeed, in a certain sense the
- VL Server is the keystone of the entire file system--when the information in the VLDB is inaccessible, the Cache Manager
- cannot retrieve files, even if the File Server processes are working properly. A list of the information stored in the VLDB
- about each volume is provided in <link linkend="HDRWQ180">Volume Information in the VLDB</link>.</para>
+ <para>The VLDB and VL Server make it possible for AFS to take
+ advantage of the increased system availability gained by using
+ multiple file server machines, because the Cache Manager knows where
+ to find a particular file. Indeed, in a certain sense the VL Server
+ is the keystone of the entire file system--when the information in
+ the VLDB is inaccessible, the Cache Manager cannot retrieve files,
+ even if the File Server processes are working properly. A list of
+ the information stored in the VLDB about each volume is provided in
+ <link linkend="HDRWQ180">Volume Information in the
+ VLDB</link>.</para>
<indexterm>
<primary>VL Server</primary>
<secondary>description</secondary>
</indexterm>
- <para>The <emphasis>Update Server</emphasis> is an optional process that helps guarantee that all file server machines are running the same version of a
- server process. System performance can be inconsistent if some machines are running one version of the BOS Server (for
- example) and other machines were running another version.</para>
-
- <para>To ensure that all machines run the same version of a process, install new software on a single file server machine of
- each system type, called the <emphasis>binary distribution machine</emphasis> for that type. The binary distribution machine
- runs the server portion of the Update Server, whereas all the other machines of that type run the client portion of the Update
- Server. The client portions check frequently with the <emphasis>server portion</emphasis> to see if they are running the right
- version of every process; if not, the <emphasis>client portion</emphasis> retrieves the right version from the binary
- distribution machine and installs it locally. The system administrator does not need to remember to install new software
- individually on all the file server machines: the Update Server does it automatically. For more on binary distribution
- machines, see <link linkend="HDRWQ93">Binary Distribution Machines</link>.</para>
+ <para>The <emphasis>Update Server</emphasis> is an optional process
+ that helps guarantee that all file server machines are running the
+ same version of a server process. System performance can be
+ inconsistent if some machines are running one version of the BOS
+ Server (for example) and other machines were running another
+ version.</para>
+
+ <para>To ensure that all machines run the same version of a process,
+ install new software on a single file server machine of each system
+ type, called the <emphasis>binary distribution machine</emphasis>
+ for that type. The binary distribution machine runs the server
+ portion of the Update Server, whereas all the other machines of that
+ type run the client portion of the Update Server. The client
+ portions check frequently with the <emphasis>server
+ portion</emphasis> to see if they are running the right version of
+ every process; if not, the <emphasis>client portion</emphasis>
+ retrieves the right version from the binary distribution machine and
+ installs it locally. The system administrator does not need to
+ remember to install new software individually on all the file server
+ machines: the Update Server does it automatically. For more on
+ binary distribution machines, see <link linkend="HDRWQ93">Binary
+ Distribution Machines</link>.</para>
<indexterm>
<primary>Update Server</primary>
<secondary>client portion</secondary>
</indexterm>
- <para>The Update Server also distributes configuration files that all file
- server machines need to store on their local disks (for a description of the contents and purpose of these files, see <link
- linkend="HDRWQ85">Common Configuration Files in the /usr/afs/etc Directory</link>). As with server process software, the need
- for consistent system performance demands that all the machines have the same version of these files.
- The system administrator needs to make changes to these files on one machine only, the cell's <emphasis>system
- control machine</emphasis>, which runs a server portion of the Update Server. All other machines in the cell run a client
- portion that accesses the correct versions of these configuration files from the system control machine. Cells running the
- international edition of AFS do not use a system control machine to distribute configuration files. For more information, see
- <link linkend="HDRWQ94">The System Control Machine</link>.</para>
+ <para>The Update Server also distributes configuration files that
+ all file server machines need to store on their local disks (for a
+ description of the contents and purpose of these files, see <link
+ linkend="HDRWQ85">Common Configuration Files in the /usr/afs/etc
+ Directory</link>). As with server process software, the need for
+ consistent system performance demands that all the machines have the
+ same version of these files. The system administrator needs to make
+ changes to these files on one machine only, the cell's
+ <emphasis>system control machine</emphasis>, which runs a server
+ portion of the Update Server. All other machines in the cell run a
+ client portion that accesses the correct versions of these
+ configuration files from the system control machine. Cells running
+ the international edition of AFS do not use a system control machine
+ to distribute configuration files. For more information, see <link
+ linkend="HDRWQ94">The System Control Machine</link>.</para>
</sect2>
<sect2 id="HDRWQ25">
<secondary>description</secondary>
</indexterm>
- <para>The <emphasis>Backup Server</emphasis> maintains the information in the <emphasis>Backup Database</emphasis>. The Backup
- Server and the Backup Database enable administrators to back up data from AFS volumes to tape and restore it from tape to the
- file system if necessary. The server and database together are referred to as the Backup System.</para>
-
- <para>Administrators initially configure the Backup System by defining sets of volumes to be dumped together and the schedule
- by which the sets are to be dumped. They also install the system's tape drives and define the drives' <emphasis>Tape
- Coordinators</emphasis>, which are the processes that control the tape drives.</para>
-
- <para>Once the Backup System is configured, user and system data can be dumped from volumes to tape or disk. In the event that data is
- ever lost from the system (for example, if a system or disk failure causes data to be lost), administrators can restore the
- data from tape. If tapes are periodically archived, or saved, data can also be restored to its state at a specific time.
- Additionally, because Backup System data is difficult to reproduce, the Backup Database itself can be backed up to tape and
- restored if it ever becomes corrupted. For more information on configuring and using the Backup System, see <link
- linkend="HDRWQ248">Configuring the AFS Backup System</link> and <link linkend="HDRWQ283">Backing Up and Restoring AFS
- Data</link>.</para>
+ <para>The <emphasis>Backup Server</emphasis> maintains the
+ information in the <emphasis>Backup Database</emphasis>. The Backup
+ Server and the Backup Database enable administrators to back up data
+ from AFS volumes to tape and restore it from tape to the file system
+ if necessary. The server and database together are referred to as
+ the Backup System.</para>
+
+ <para>Administrators initially configure the Backup System by
+ defining sets of volumes to be dumped together and the schedule by
+ which the sets are to be dumped. They also install the system's tape
+ drives and define the drives' <emphasis>Tape
+ Coordinators</emphasis>, which are the processes that control the
+ tape drives.</para>
+
+ <para>Once the Backup System is configured, user and system data can
+ be dumped from volumes to tape or disk. In the event that data is
+ ever lost from the system (for example, if a system or disk failure
+ causes data to be lost), administrators can restore the data from
+ tape. If tapes are periodically archived, or saved, data can also be
+ restored to its state at a specific time. Additionally, because
+ Backup System data is difficult to reproduce, the Backup Database
+ itself can be backed up to tape and restored if it ever becomes
+ corrupted. For more information on configuring and using the Backup
+ System, see <link linkend="HDRWQ248">Configuring the AFS Backup
+ System</link> and <link linkend="HDRWQ283">Backing Up and Restoring
+ AFS Data</link>.</para>
</sect2>
<sect2 id="HDRWQ26">
<secondary>description</secondary>
</indexterm>
- <para>The <emphasis>Salvager</emphasis> differs from other AFS Servers in that it runs only at selected times. The BOS Server
- invokes the Salvager when the File Server, Volume Server, or both fail. The Salvager attempts to repair disk corruption that
- can result from a failure.</para>
+ <para>The <emphasis>Salvager</emphasis> differs from other AFS
+ Servers in that it runs only at selected times. The BOS Server
+ invokes the Salvager when the File Server, Volume Server, or both
+ fail. The Salvager attempts to repair disk corruption that can
+ result from a failure.</para>
- <para>As a system administrator, you can also invoke the Salvager as necessary, even if the File Server or Volume Server has
- not failed. See <link linkend="HDRWQ232">Salvaging Volumes</link>.</para>
+ <para>As a system administrator, you can also invoke the Salvager as
+ necessary, even if the File Server or Volume Server has not
+ failed. See <link linkend="HDRWQ232">Salvaging
+ Volumes</link>.</para>
</sect2>
<sect2 id="HDRWQ27">
<secondary>description</secondary>
</indexterm>
- <para>The <emphasis>Network Time Protocol Daemon (NTPD)</emphasis> is not an AFS server process per se, but plays an important
- role. It helps guarantee that all of the file server machines and client machines agree on the time. The NTPD on all file server machines learns the correct time from a parent NTPD source, which may be located inside or outside the cell.</para>
-
- <para>Keeping clocks synchronized is particularly important to the correct operation of AFS's distributed database technology,
- which coordinates the copies of the Backup, Protection, and Volume Location Databases; see <link
- linkend="HDRWQ52">Replicating the OpenAFS Administrative Databases</link>. Client machines may also refer to these clocks for the
- correct time; therefore, it is less confusing if all file server machines have the same time. For more technical detail about
- the NTPD, see <ulink url="http://www.ntp.org/">The NTP web site</ulink> or the documentation for your operating system.</para>
-
- <important><title>Clock Skew Impact</title>
- <para>Client machines that are authenticating to an OpenAFS cell
- with valid credentials may still fail when the clocks of the client
- machine, Kerberos server, and the fileserver machines are not in
+ <para>The <emphasis>Network Time Protocol Daemon (NTPD)</emphasis>
+ is not an AFS server process per se, but plays an important role. It
+ helps guarantee that all of the file server machines and client
+ machines agree on the time. The NTPD on all file server machines
+ learns the correct time from a parent NTPD source, which may be
+ located inside or outside the cell.</para>
+
+ <para>Keeping clocks synchronized is particularly important to the
+ correct operation of AFS's distributed database technology, which
+ coordinates the copies of the Backup, Protection, and Volume
+ Location Databases; see <link linkend="HDRWQ52">Replicating the
+ OpenAFS Administrative Databases</link>. Client machines may also
+ refer to these clocks for the correct time; therefore, it is less
+ confusing if all file server machines have the same time. For more
+ technical detail about the NTPD, see <ulink
+ url="http://www.ntp.org/">The NTP web site</ulink> or the
+ documentation for your operating system.</para>
+
+ <important><title>Clock Skew Impact</title> <para>Client machines
+ that are authenticating to an OpenAFS cell with valid credentials
+ may still fail when the clocks of the client machine, Kerberos
+ server, and the fileserver machines are not in
sync.</para></important>
- <note><title>Legacy runntp</title>
- <para>It is no longer recommended to run the legacy NTPD process
- called <emphasis>runntp</emphasis> that is part of the OpenAFS
- suite. Running the NTPD software that comes with your operating
- system or from <ulink url="http://www.ntp.org/">www.ntp.org</ulink>
- is preferred.</para></note>
+ <note><title>Legacy runntp</title> <para>It is no longer recommended
+ to run the legacy NTPD process called <emphasis>runntp</emphasis>
+ that is part of the OpenAFS suite. Running the NTPD software that
+ comes with your operating system or from <ulink
+ url="http://www.ntp.org/">www.ntp.org</ulink> is
+ preferred.</para></note>
</sect2>
<secondary>functions of</secondary>
</indexterm>
- <para>As already mentioned in <link linkend="HDRWQ16">Caching and Callbacks</link>, the <emphasis>Cache Manager</emphasis> is
- the one component in this section that resides on client machines rather than on file server machines. It is not technically a
- stand-alone process, but rather a set of extensions or modifications in the client machine's kernel that enable communication
- with the server processes running on server machines. Its main duty is to translate file requests (made by application
- programs on client machines) into <emphasis>remote procedure calls (RPCs)</emphasis> to the File Server. (The Cache Manager
- first contacts the VL Server to find out which File Server currently houses the volume that contains a requested file, as
- mentioned in <link linkend="HDRWQ23">The Volume Location (VL) Server</link>). When the Cache Manager receives the requested
- file, it caches it before passing data on to the application program.</para>
-
- <para>The Cache Manager also tracks the state of files in its cache compared to the version at the File Server by storing the
- callbacks sent by the File Server. When the File Server breaks a callback, indicating that a file or volume changed, the Cache
- Manager requests a copy of the new version before providing more data to application programs.</para>
+ <para>As already mentioned in <link linkend="HDRWQ16">Caching and
+ Callbacks</link>, the <emphasis>Cache Manager</emphasis> is the one
+ component in this section that resides on client machines rather
+ than on file server machines. It is not technically a stand-alone
+ process, but rather a set of extensions or modifications in the
+ client machine's kernel that enable communication with the server
+ processes running on server machines. Its main duty is to translate
+ file requests (made by application programs on client machines) into
+ <emphasis>remote procedure calls (RPCs)</emphasis> to the File
+ Server. (The Cache Manager first contacts the VL Server to find out
+ which File Server currently houses the volume that contains a
+ requested file, as mentioned in <link linkend="HDRWQ23">The Volume
+ Location (VL) Server</link>). When the Cache Manager receives the
+ requested file, it caches it before passing data on to the
+ application program.</para>
+
+ <para>The Cache Manager also tracks the state of files in its cache
+ compared to the version at the File Server by storing the callbacks
+ sent by the File Server. When the File Server breaks a callback,
+ indicating that a file or volume changed, the Cache Manager requests
+ a copy of the new version before providing more data to application
+ programs.</para>
</sect2>
</sect1>
</chapter>
git://git.openafs.org / openafs.git / blobdiff