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<H1>User Guide</H1>
<HR><P ALIGN="center"> <A HREF="../index.htm"><IMG SRC="../books.gif" BORDER="0" ALT="[Return to Library]"></A> <A HREF="auusg002.htm#ToC"><IMG SRC="../toc.gif" BORDER="0" ALT="[Contents]"></A> <A HREF="auusg003.htm"><IMG SRC="../prev.gif" BORDER="0" ALT="[Previous Topic]"></A> <A HREF="#Bot_Of_Page"><IMG SRC="../bot.gif" BORDER="0" ALT="[Bottom of Topic]"></A> <A HREF="auusg005.htm"><IMG SRC="../next.gif" BORDER="0" ALT="[Next Topic]"></A> <A HREF="auusg013.htm#HDRINDEX"><IMG SRC="../index.gif" BORDER="0" ALT="[Index]"></A> <P>
<HR><H1><A NAME="HDRWQ2" HREF="auusg002.htm#ToC_7">An Introduction to AFS</A></H1>
<P>This chapter introduces basic AFS concepts and terms.
It assumes that you are already familiar with standard UNIX commands, file
protection, and pathname conventions.
<HR><H2><A NAME="HDRWQ3" HREF="auusg002.htm#ToC_8">AFS Concepts</A></H2>
<P>AFS makes it easy for people to work together on the same
files, no matter where the files are located. AFS users do not have to
know which machine is storing a file, and administrators can move files from
machine to machine without interrupting user access. Users always
identify a file by the same pathname and AFS finds the correct file
automatically, just as happens in the local file system on a single
machine. While AFS makes file sharing easy, it does not compromise the
security of the shared files. It provides a sophisticated protection
scheme.
<A NAME="IDX747"></A>
<A NAME="IDX748"></A>
<P><H3><A NAME="Header_9" HREF="auusg002.htm#ToC_9">Client/Server Computing</A></H3>
<P>AFS uses a <I>client/server computing</I> model. In
client/server computing, there are two types of machines. <I>Server
machines</I> store data and perform services for client machines.
<I>Client machines</I> perform computations for users and access data and
services provided by server machines. Some machines act as both clients
and servers. In most cases, you work on a client machine, accessing
files stored on a file server machine.
<A NAME="IDX749"></A>
<A NAME="IDX750"></A>
<A NAME="IDX751"></A>
<A NAME="IDX752"></A>
<A NAME="IDX753"></A>
<A NAME="IDX754"></A>
<P><H3><A NAME="Header_10" HREF="auusg002.htm#ToC_10">Distributed File Systems</A></H3>
<P>AFS is a <I>distributed file system</I> which joins together the
file systems of multiple file server machines, making it as easy to access
files stored on a remote file server machine as files stored on the local
disk. A distributed file system has two main advantages over a
conventional centralized file system:
<A NAME="IDX755"></A>
<UL>
<P><LI>Increased availability: A copy of a popular file, such as the binary
for an application program, can be stored on many file server machines.
An outage on a single machine or even multiple machines does not necessarily
make the file unavailable. Instead, user requests for the program are
routed to accessible machines. With a centralized file system, the loss
of the central file storage machine effectively shuts down the entire
system.
<P><LI>Increased efficiency: In a distributed file system, the work load is
distributed over many smaller file server machines that tend to be more fully
utilized than the larger (and usually more expensive) file storage machine of
a centralized file system.
</UL>
<P>AFS hides its distributed nature, so working with AFS files looks and feels
like working with files stored on your local machine, except that you can
access many more files. And because AFS relies on the power of
users' client machines for computation, increasing the number of AFS
users does not slow AFS performance appreciably, making it a very efficient
computing environment.
<P><H3><A NAME="HDRWQ4" HREF="auusg002.htm#ToC_11">AFS Filespace and Local Filespace</A></H3>
<A NAME="IDX756"></A>
<P>AFS acts as an extension of your machine's local UNIX file
system. Your system administrator creates a directory on the local disk
of each AFS client machine to act as a gateway to AFS. By convention,
this directory is called <B>/afs</B>, and it functions as the root of the
<I>AFS filespace</I>.
<A NAME="IDX757"></A>
<A NAME="IDX758"></A>
<A NAME="IDX759"></A>
<P>Just like the UNIX file system, AFS uses a hierarchical file structure (a
tree). Under the <B>/afs</B> root directory are subdirectories
created by your system administrator, including your home directory.
Other directories that are at the same level of the local file system as
<B>/afs</B>, such as <B>/usr</B>, <B>/etc</B>, or <B>/bin</B>,
can either be located on your local disk or be links to AFS
directories. Files relevant only to the local machine are usually
stored on the local machine. All other files can be stored in AFS,
enabling many users to share them and freeing the local machine's disk
space for other uses.
<TABLE><TR><TD ALIGN="LEFT" VALIGN="TOP"><B>Note:</B></TD><TD ALIGN="LEFT" VALIGN="TOP">You can use AFS commands only on files in the AFS filespace or the local
directories that are links to the AFS filespace.
</TD></TR></TABLE>
<P><H3><A NAME="HDRWQ5" HREF="auusg002.htm#ToC_12">Cells and Sites</A></H3>
<P>The <I>cell</I> is the administrative domain in
AFS. Each cell's administrators determine how client machines are
configured and how much storage space is available to each user. The
organization corresponding to a cell can be a company, a university
department, or any defined group of users. From a hardware perspective,
a cell is a grouping of client machines and server machines defined to belong
to the same cell.
<A NAME="IDX760"></A>
An AFS <I>site</I> is a grouping of one or more related cells. For
example, the cells at the ABC Corporation form a single site.
<A NAME="IDX761"></A>
<P>By convention, the subdirectories of the <B>/afs</B> directory are
cellular filespaces, each of which contains subdirectories and files that
belong to a single cell. For example, directories and files relevant to
the ABC Corporation cell are stored in the subdirectory
<B>/afs/abc.com</B>.
<P>While each cell organizes and maintains its own filespace, it can also
connect with the filespace of other AFS cells. The result is a huge
filespace that enables file sharing within and across cells.
<A NAME="IDX762"></A>
<P>The cell to which your client machine belongs is called your <I>local
cell</I>. All other cells in the AFS filespace are termed
<I>foreign cells</I>.
<A NAME="IDX763"></A>
<A NAME="IDX764"></A>
<A NAME="IDX765"></A>
<P><H3><A NAME="HDRWQ6" HREF="auusg002.htm#ToC_13">Volumes and Mount Points</A></H3>
<P>The storage disks in a computer are divided into sections
called <I>partitions</I>. AFS further divides partitions into units
called <I>volumes</I>, each of which houses a subtree of related files and
directories. The volume provides a convenient container for storing
related files and directories. Your system administrators can move
volumes from one file server machine to another without your noticing, because
AFS automatically tracks a volume's location.
<A NAME="IDX766"></A>
<A NAME="IDX767"></A>
<P>You access the contents of a volume by accessing its <I>mount point</I>
in the AFS filespace. A mount point is a special file system element
that looks and acts like a regular UNIX directory, but tells AFS the
volume's name. When you change to a different directory (by using
the <B>cd</B> command, for example) you sometimes <I>cross</I> a mount
point and start accessing the contents of a different volume than
before. You normally do not notice the crossing, however, because AFS
automatically interprets mount points and retrieves the contents of the new
directory from the appropriate volume. You do not need to track which
volume, partition, or file server machine is housing a directory's
contents. If you are interested, though, you can learn a volume's
location; for instructions, see <A HREF="auusg006.htm#HDRWQ40">Locating Files and Directories</A>.
<A NAME="IDX768"></A>
<A NAME="IDX769"></A>
<P>If your system administrator has followed the conventional practice, your
home directory corresponds to one volume, which keeps its contents together on
one partition of a file server machine. User volumes are typically
named <B>user.</B><VAR>username</VAR>. For example, the volume
for a user named <B>smith</B> in the cell <B>abc.com</B> is
called <B>user.smith</B> and is mounted at the directory
<B>/afs/abc.com/usr/smith</B>.
<A NAME="IDX770"></A>
<P>Because AFS volumes are stored on different file server machines, when a
machine becomes unavailable only the volumes on that machine are
inaccessible. Volumes stored on other machines are still
accessible. However, if a volume's mount point resides in a volume
that is stored on an unavailable machine, the former volume is also
inaccessible. For that reason, volumes containing frequently used
directories (for example, <B>/afs</B> and
<B>/afs/</B><VAR>cellname</VAR>) are often copied and distributed to many
file server machines.
<P><H3><A NAME="HDRWQ7" HREF="auusg002.htm#ToC_14">Volume Quotas</A></H3>
<A NAME="IDX771"></A>
<P>Each volume has a size limit, or <I>quota</I>, assigned by the system
administrator. A volume's quota determines the maximum amount of
disk space the volume can consume. If you attempt to exceed a
volume's quota, you receive an error message. For instructions on
checking volume quota, see <A HREF="auusg006.htm#HDRWQ39">Displaying Volume Quota</A>.
<P>Volumes have completely independent quotas. For example, say that
the current working directory is <B>/afs/abc.com/usr/smith</B>,
which is the mount point for the <B>user.smith</B> volume with 1000
free blocks. You try to copy a 500 block file from the current working
directory to the <B>/afs/abc.com/usr/pat</B> directory, the mount
point for the volume <B>user.pat</B>. However, you get an
error message saying there is not enough space. You check the volume
quota for <B>user.pat</B>, and find that the volume only has 50
free blocks.
<HR><H2><A NAME="HDRWQ8" HREF="auusg002.htm#ToC_15">Using Files in AFS</A></H2>
<P><H3><A NAME="HDRWQ9" HREF="auusg002.htm#ToC_16">The Cache Manager</A></H3>
<P>You can access the AFS filespace only when working on an AFS
client machine. The <I>Cache Manager</I> on that machine is your
agent in accessing information stored in the AFS filespace. When you
access a file, the Cache Manager on your client machine requests the file from
the appropriate file server machine and stores (<I>caches</I>) a copy of
it on your client machine's local disk. Application programs on
your client machine use the local, cached copy of the file. This
improves performance because it is much faster to use a local file than to
send requests for file data across the network to the file server
machine.
<A NAME="IDX772"></A>
<A NAME="IDX773"></A>
<A NAME="IDX774"></A>
<A NAME="IDX775"></A>
<P>Because application programs use the cached copy of a file, any changes you
make are not necessarily stored permanently to the central version stored on
the file server machine until the file closes. At that point, the Cache
Manager writes your changes back to the file server machine, where they
replace the corresponding parts of the existing file. Some application
programs close a file in this way each time you issue their <B>save</B>
command (and then immediately reopen the file so that you can continue
working). With other programs, issuing the <B>save</B> command
writes the changes only to the local cached copy. If you use the latter
type of text editor, you need to close the file periodically to make sure your
changes are stored permanently.
<P>If a file server machine becomes inaccessible, you can continue working
with the local, cached copy of a file fetched from that machine, but you
cannot save your changes permanently until the server machine is again
accessible.
<P><H3><A NAME="HDRWQ10" HREF="auusg002.htm#ToC_17">Updating Copies of Cached Files</A></H3>
<A NAME="IDX776"></A>
<A NAME="IDX777"></A>
<P>When the central version of a file changes on the file server machine, the
AFS <I>File Server</I> process running on that machine advises all other
Cache Managers with copies of that file that their version is no longer
valid. AFS has a special mechanism for performing these notifications
efficiently. When the File Server sends the Cache Manager a copy of a
modifiable file, it also sends a <I>callback</I>. A callback
functions as a promise from the File Server to contact the Cache Manager if
the centrally stored copy of the file is changed while it is being
used. If that happens, the File Server <I>breaks</I> the
callback. If you run a program that requests data from the changed
file, the Cache Manager notices the broken callback and gets an updated copy
of the file from the File Server. Callbacks ensure that you are working
with the most recent copy of a file.
<TABLE><TR><TD ALIGN="LEFT" VALIGN="TOP"><B>Note:</B></TD><TD ALIGN="LEFT" VALIGN="TOP">The callback mechanism does not guarantee that you immediately see the
changes someone else makes to a file you are using. Your Cache Manager
does not notice the broken callback until your application program asks it for
more data from the file.
</TD></TR></TABLE>
<P><H3><A NAME="Header_18" HREF="auusg002.htm#ToC_18">Multiple Users Modifying Files</A></H3>
<A NAME="IDX778"></A>
<A NAME="IDX779"></A>
<P>Like a standard UNIX file system, AFS preserves only the changes to a file
that are saved last, regardless of who made the changes. When
collaborating with someone on the same files, you must coordinate your work to
avoid overwriting each other's changes. You can use AFS access
control lists (ACLs) to limit the ability of other users to access or change
your files, and so prevent them from accidentally overwriting your
files. See <A HREF="auusg007.htm#HDRWQ44">Protecting Your Directories and Files</A>.
<HR><H2><A NAME="HDRWQ11" HREF="auusg002.htm#ToC_19">AFS Security</A></H2>
<A NAME="IDX780"></A>
<A NAME="IDX781"></A>
<P>AFS makes it easy for many users to access the same files, but also uses
several mechanisms to ensure that only authorized users access the AFS
filespace. The mechanisms include the following:
<UL>
<P><LI>Passwords and mutual authentication ensure that only authorized users
access AFS filespace
<P><LI>Access control lists enable users to restrict or permit access to their
own directories
</UL>
<P><H3><A NAME="HDRWQ12" HREF="auusg002.htm#ToC_20">Passwords and Mutual Authentication</A></H3>
<A NAME="IDX782"></A>
<A NAME="IDX783"></A>
<A NAME="IDX784"></A>
<P>AFS uses two related mechanisms to ensure that only authorized users access
the filespace: passwords and mutual authentication. Both
mechanisms require that a user prove his or her identity.
<P>When you first identify yourself to AFS, you must provide the password
associated with your username, to prove that you are who you say you
are. When you provide the correct password, you become
<I>authenticated</I> and your Cache Manager receives a
<I>token</I>. A token is a package of information that is scrambled
by an AFS authentication program using your AFS password as a key. Your
Cache Manager can unscramble the token because it knows your password and
AFS's method of scrambling.
<A NAME="IDX785"></A>
<A NAME="IDX786"></A>
<P>The token acts as proof to AFS server programs that you are authenticated
as a valid AFS user. It serves as the basis for the second means
through which AFS creates security, called <I>mutual
authentication</I>. Under mutual authentication, both parties
communicating across the network prove their identities to one another.
AFS requires mutual authentication whenever a server and client (most often, a
Cache Manager) communicate with each other.
<P>The mutual authentication protocol that AFS uses is designed to make it
very difficult for people to authenticate fraudulently. When your Cache
Manager contacts a File Server on your behalf, it sends the token you obtained
when you authenticated. The token is encrypted with a key that only an
AFS File Server can know. If the File Server can decrypt your token, it
can communicate with your Cache Manager. In turn, the Cache Manager
accepts the File Server as genuine because the File Server can decrypt and use
the information in the token.
<A NAME="IDX787"></A>
<P><H3><A NAME="Header_21" HREF="auusg002.htm#ToC_21">Access Control Lists</A></H3>
<A NAME="IDX788"></A>
<P>AFS uses <I>access control lists</I> (<I>ACLs</I>) to determine who
can access the information in the AFS filespace. Each AFS directory has
an ACL to specify what actions different users can perform on that directory
and its files. An ACL can contain up to about 20 entries for users,
groups, or both; each entry lists a user or group and the permissions it
possesses.
<P>The owner of a directory and system administrators can always administer an
ACL. Users automatically own their home directories and
subdirectories. Other non-owner users can define a directory's ACL
only if specifically granted that permission on the ACL. For more
information on ACLs, see <A HREF="auusg007.htm#HDRWQ44">Protecting Your Directories and Files</A>
.
<P>A group is composed of one or more users and client machines. If a
user belongs to a group that appears on an ACL, the user gets all of the
permissions granted to that group, just as if the user were listed directly on
the ACL. Similarly, if a user is logged into a client machine that
belongs to a group, the user has all of the permissions granted to that
group. For instructions on defining and using groups, see <A HREF="auusg008.htm#HDRWQ60">Using Groups</A>.
<P>All users who can access your cell's filespace, authenticated or not,
are automatically assigned to a group called
<B>system:anyuser</B>. For a discussion of placing the
<B>system:anyuser</B> group on ACLs, see <A HREF="auusg007.htm#HDRWQ51">Extending Access to Users from Foreign Cells</A>.
<TABLE><TR><TD ALIGN="LEFT" VALIGN="TOP"><B>Note:</B></TD><TD ALIGN="LEFT" VALIGN="TOP">You can use the UNIX mode bits to control access on specific files within an
AFS directory; however, the effect of these mode bits is different under
AFS than in the standard UNIX file system. See <A HREF="#HDRWQ16">File and Directory Protection</A>.
</TD></TR></TABLE>
<HR><H2><A NAME="HDRWQ13" HREF="auusg002.htm#ToC_22">Differences Between UNIX and AFS</A></H2>
<P>AFS is designed to be similar to the UNIX file system.
For instance, many of the basic UNIX file manipulation commands (<B>cp</B>
for copy, <B>rm</B> for remove, and so on) are the same in AFS as they are
as in UNIX. All of your application programs work as they did
before. The following sections describe some of the differences between
a standard UNIX file system and AFS.
<P><H3><A NAME="HDRWQ14" HREF="auusg002.htm#ToC_23">File Sharing</A></H3>
<A NAME="IDX789"></A>
<A NAME="IDX790"></A>
<A NAME="IDX791"></A>
<P>AFS enables users to share remote files as easily as local files. To
access a file on a remote machine in AFS, you simply specify the file's
pathname. In contrast, to access a file in a remote machine's UNIX
file system, you must log into the remote machine or create a mount point on
the local machine that points to a directory in the remote machine's UNIX
file system.
<P>AFS users can see and share all the files under the <B>/afs</B> root
directory, given the appropriate privileges. An AFS user who has the
necessary privileges can access a file in any AFS cell, simply by specifying
the file's pathname. File sharing in AFS is not restricted by
geographical distances or operating system differences.
<P><H3><A NAME="HDRWQ15" HREF="auusg002.htm#ToC_24">Login and Authentication</A></H3>
<A NAME="IDX792"></A>
<P>To become an authenticated AFS user, you need to provide a password to
AFS.
<UL>
<P><LI>On machines that use an AFS-modified login utility, logging in is a
one-step process; your initial login automatically authenticates you with
AFS.
<P><LI>On machines that do not use an AFS-modified login utility, you must
perform two steps.
<OL TYPE=1>
<P><LI>Log in to your local machine.
<P><LI>Issue the <B>klog</B> command with the <B>-setpag</B> argument to
authenticate with AFS and get your token.
</OL>
</UL>
<P>Your system administrator can tell you whether your machine uses an
AFS-modified login utility or not. Then see the login instructions in <A HREF="auusg005.htm#HDRWQ21">Logging in and Authenticating with AFS</A>.
<P>AFS authentication passwords are stored in special AFS database, rather
than in the local password file (<B>/etc/passwd</B> or equivalent).
If your machine uses an AFS-modified login utility, you can change your
password with a single command. If your machine does not use an
AFS-modified login utility, you must issue separate commands to change your
AFS and local passwords. See <A HREF="auusg005.htm#HDRWQ36">Changing Your Password</A>.
<A NAME="IDX793"></A>
<A NAME="IDX794"></A>
<A NAME="IDX795"></A>
<P><H3><A NAME="HDRWQ16" HREF="auusg002.htm#ToC_25">File and Directory Protection</A></H3>
<A NAME="IDX796"></A>
<A NAME="IDX797"></A>
<P>AFS does not rely on the mode bit protections of a standard UNIX system
(though its protection system does interact with these mode bits).
Instead, AFS uses an access control list (ACL) to control access to each
directory and its contents. The following list summarizes the
differences between the two methods:
<UL>
<P><LI>UNIX mode bits specify three types of access permissions:
<B>r</B> (<B>read</B>), <B>w</B> (<B>write</B>), and
<B>x</B> (<B>execute</B>). An AFS ACL uses seven types of
permissions: <B>r</B> (<B>read</B>), <B>l</B>
(<B>lookup</B>), <B>i</B> (<B>insert</B>), <B>d</B>
(<B>delete</B>), <B>w</B> (<B>write</B>), <B>k</B>
(<B>lock</B>), and <B>a</B> (<B>administer</B>). For more
information, see <A HREF="auusg007.htm#HDRWQ46">The AFS ACL Permissions</A> and <A HREF="auusg007.htm#HDRWQ59">How AFS Uses the UNIX Mode Bits</A>.
<P><LI>The three sets of mode bits on each UNIX file or directory enable you to
grant permissions to three users or groups of users: the file or
directory's owner, the group that owns the file or directory, and all
other users. An ACL can accommodate up to about 20 entries, each of
which extends certain permissions to a user or group. Unlike standard
UNIX, a user can belong to an unlimited number of groups, and groups can be
defined by both users and system administrators. See <A HREF="auusg008.htm#HDRWQ60">Using Groups</A>.
<P><LI>UNIX mode bits are set individually on each file and directory. An
ACL applies to all of the files in a directory. While at first glance
the AFS method possibly seems less precise, in actuality (given a proper
directory structure) there are no major disadvantages to directory-level
protections and they are easier to establish and maintain.
</UL>
<P><H3><A NAME="HDRWQ17" HREF="auusg002.htm#ToC_26">Machine Outages</A></H3>
<P>The kinds of failures you experience when a standard UNIX
file system goes down are different than when one or more individual AFS file
server machines become unavailable. When a standard UNIX file system is
inaccessible, the system simply locks up and you can lose changes to any files
with which you were working.
<P>When an AFS file server machine becomes inaccessible, you cannot access the
files on that machine. If a copy of the file is available from another
file server machine, however, you do not necessarily even notice the server
outage. This is because AFS gives your cell's system
administrators the ability to store copies of popular programs on multiple
file servers. The Cache Manager chooses between the copies
automatically; when one copy becomes unavailable, the Cache Manager
simply chooses another.
<P>If there are no other copies of a file that is stored on an inaccessible
server machine, you can usually continue to use the copy stored in your client
machine's local AFS cache. However, you cannot save changes to
files stored on an inaccessible file server machine until it is accessible
again.
<P><H3><A NAME="HDRWQ18" HREF="auusg002.htm#ToC_27">Remote Commands</A></H3>
<P>
<A NAME="IDX798"></A>
<A NAME="IDX799"></A>
<A NAME="IDX800"></A>
<A NAME="IDX801"></A>
<A NAME="IDX802"></A>
<A NAME="IDX803"></A>
<A NAME="IDX804"></A>
<A NAME="IDX805"></A>
The UNIX <I>remote commands</I> enable you to run programs on a remote
machine without establishing a connection to it by using a program such as
<B>telnet</B>. Many of the remote commands (such as <B>ftp</B>,
<B>rcp</B>, and <B>rsh</B>) remain available in AFS, depending on how
your administrators have configured them. If the remote machine has a
Cache Manager, your token is used there also and you are authenticated while
the remote command runs. If the remote machine does not run a Cache
Manager, you receive the following message:
<PRE> Warning: unable to authenticate.
</PRE>
<P>In this case, you are logged into the remote machine's UNIX file
system, but you are not authenticated to AFS. You can access the local
files on the remote machine and the AFS directories that grant access to the
<B>system:anyuser</B> group, but you cannot access protected AFS
directories.
<P><H3><A NAME="Header_28" HREF="auusg002.htm#ToC_28">Differences in the Semantics of Standard UNIX Commands</A></H3>
<P>This section summarizes differences in the functionality of some
commonly issued UNIX commands.
<DL>
<P><DT><B>chmod
<A NAME="IDX806"></A>
<A NAME="IDX807"></A>
</B><DD>Only members of the <B>system:administrators</B> group can use
this command to turn on the setuid, setgid or sticky mode bits on AFS
files. (For more information about this group, see <A HREF="auusg007.htm#HDRWQ50">Using the System Groups on ACLs</A>.)
<P><DT><B>chown
<A NAME="IDX808"></A>
<A NAME="IDX809"></A>
</B><DD>Only members of the <B>system:administrators</B> group can issue
this command on AFS files.
<P><DT><B>chgrp
<A NAME="IDX810"></A>
<A NAME="IDX811"></A>
</B><DD>Only members of the <B>system:administrators</B> group can issue
this command on AFS files and directories.
<P><DT><B>groups
<A NAME="IDX812"></A>
<A NAME="IDX813"></A>
</B><DD>If the user's AFS tokens are identified by a process authentication
group (PAG), the output of this command includes two large numbers. For
a description of PAGs, see <A HREF="auusg005.htm#HDRWQ24">Authenticating with AFS</A>.
<P><DT><B>inetd
<A NAME="IDX814"></A>
<A NAME="IDX815"></A>
</B><DD>The AFS version of this daemon authenticates remote issuers of the
AFS-modified <B>rcp</B> and <B>rsh</B> commands with AFS.
<P><DT><B>login utilities
<A NAME="IDX816"></A>
</B><DD>AFS-modified login utilities both log you into the local UNIX file system
and authenticate you with AFS.
<P><DT><B>ln
<A NAME="IDX817"></A>
<A NAME="IDX818"></A>
</B><DD>You cannot use this command to create a hard link between files that
reside in different AFS directories. You must add the <B>-s</B>
option to create a symbolic link instead.
</DL>
<HR><H2><A NAME="HDRWQ19" HREF="auusg002.htm#ToC_29">Using AFS with NFS</A></H2>
<P>Some cells use the Networking File System (NFS) in addition
to AFS. If you work on an NFS client machine, your system administrator
can configure it to access the AFS filespace through a program called the
<I>NFS/AFS Translator</I><SUP>TM</SUP>. See <A HREF="auusg010.htm#HDRWQ80">Appendix A, Using the NFS/AFS Translator</A>.
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