-.TH EXPORTS 5 "4 March 2005" "Linux" "Linux File Formats Manual"
+.\"@(#)exports.5"
+.\"
+.TH exports 5 "31 December 2009"
.SH NAME
-exports \- NFS file systems being exported (for Kernel based NFS)
-.SH SYNOPSIS
-.B /etc/exports
+exports \- NFS server export table
.SH DESCRIPTION
The file
.I /etc/exports
-serves as the access control list for file systems which may be
-exported to NFS clients. It is used by
-.IR exportfs (8)
+contains a table of local physical file systems on an NFS server
+that are accessible to NFS clients.
+The contents of the file are maintained by the server's system
+administrator.
+.PP
+Each file system in this table has a list of options and an
+access control list.
+The table is used by
+.BR exportfs (8)
to give information to
-.IR mountd (8)
-and to the kernel based NFS file server daemon
-.IR nfsd (8).
+.BR mountd (8).
.PP
The file format is similar to the SunOS
.I exports
the export name using a backslash followed by the character code as three
octal digits.
.PP
+To apply changes to this file, run
+.BR exportfs \-ra
+or restart the NFS server.
+.PP
.SS Machine Name Formats
NFS clients may be specified in a number of ways:
.IP "single host
as
.IR address/netmask
where the netmask can be specified in dotted-decimal format, or as a
-contiguous mask length (for example, either `/255.255.252.0' or `/22' appended
-to the network base address result in identical subnetworks with 10 bits of
-host). Wildcard characters generally do not work on IP addresses, though they
+contiguous mask length.
+For example, either `/255.255.252.0' or `/22' appended
+to the network base IPv4 address results in identical subnetworks with 10 bits of
+host. Wildcard characters generally do not work on IP addresses, though they
may work by accident when reverse DNS lookups fail.
'''.TP
'''.B =public
'''option. Multiple specifications of a public root will be ignored.
.PP
.SS RPCSEC_GSS security
-To restrict access to an export using rpcsec_gss security, use the special
-string "gss/krb5" as the client. It is not possible to simultaneously require
-rpcsec_gss and to make requirements on the IP address of the client.
+You may use the special strings "gss/krb5", "gss/krb5i", or "gss/krb5p"
+to restrict access to clients using rpcsec_gss security. However, this
+syntax is deprecated; on linux kernels since 2.6.23, you should instead
+use the "sec=" export option:
+.TP
+.IR sec=
+The sec= option, followed by a colon-delimited list of security flavors,
+restricts the export to clients using those flavors. Available security
+flavors include sys (the default--no cryptographic security), krb5
+(authentication only), krb5i (integrity protection), and krb5p (privacy
+protection). For the purposes of security flavor negotiation, order
+counts: preferred flavors should be listed first. The order of the sec=
+option with respect to the other options does not matter, unless you
+want some options to be enforced differently depending on flavor.
+In that case you may include multiple sec= options, and following options
+will be enforced only for access using flavors listed in the immediately
+preceding sec= option. The only options that are permitted to vary in
+this way are ro, rw, no_root_squash, root_squash, and all_squash.
.PP
.SS General Options
-.IR exportfs
+.BR exportfs
understands the following export options:
.TP
.IR secure "\*d
above).
In releases of nfs-utils up to and including 1.0.0, this option was the
-default. In all subsequence releases,
+default. In all releases after 1.0.0,
.I sync
is the default, and
.I async
-must be explicit requested if needed.
-To help make system administrators aware of this change, 'exportfs'
+must be explicitly requested if needed.
+To help make system administrators aware of this change,
+.B exportfs
will issue a warning if neither
.I sync
nor
option is currently only effective on
.I "single host
exports. It does not work reliably with netgroup, subnet, or wildcard
-exports.
+exports.
This option can be very useful in some situations, but it should be
used with due care, and only after confirming that the client system
that option in the
.B exports
file. If you put neither option,
-.I exportfs
+.B exportfs
will warn you that the change is pending.
.TP
.TP
.IR no_acl
On some specially patched kernels, and when exporting filesystems that
-support ACLs, this option tells nfsd not to reveal ACLs to clients, so
+support ACLs, this option tells
+.B nfsd
+not to reveal ACLs to clients, so
they will see only a subset of actual permissions on the given file
system. This option is safe for filesystems used by NFSv2 clients and
old NFSv3 clients that perform access decisions locally. Current
exported.
.TP
-.IR fsid= num
-This option forces the filesystem identification portion of the file
-handle and file attributes used on the wire to be
-.I num
-instead of a number derived from the major and minor number of the
-block device on which the filesystem is mounted. Any 32 bit number
-can be used, but it must be unique amongst all the exported filesystems.
+.IR fsid= num|root|uuid
+NFS needs to be able to identify each filesystem that it exports.
+Normally it will use a UUID for the filesystem (if the filesystem has
+such a thing) or the device number of the device holding the
+filesystem (if the filesystem is stored on the device).
+
+As not all filesystems are stored on devices, and not all filesystems
+have UUIDs, it is sometimes necessary to explicitly tell NFS how to
+identify a filesystem. This is done with the
+.I fsid=
+option.
+
+For NFSv4, there is a distinguished filesystem which is the root of
+all exported filesystem. This is specified with
+.I fsid=root
+or
+.I fsid=0
+both of which mean exactly the same thing.
-This can be useful for NFS failover, to ensure that both servers of
-the failover pair use the same NFS file handles for the shared filesystem
-thus avoiding stale file handles after failover.
+Other filesystems can be identified with a small integer, or a UUID
+which should contain 32 hex digits and arbitrary punctuation.
-Some Linux filesystems are not mounted on a block device; exporting
-these via NFS requires the use of the
-.I fsid
-option (although that may still not be enough).
+Linux kernels version 2.6.20 and earlier do not understand the UUID
+setting so a small integer must be used if an fsid option needs to be
+set for such kernels. Setting both a small number and a UUID is
+supported so the same configuration can be made to work on old and new
+kernels alike.
-The value 0 has a special meaning when use with NFSv4. NFSv4 has a
-concept of a root of the overall exported filesystem. The export point
-exported with fsid=0 will be used as this root.
+.TP
+.IR refer= path@host[+host][:path@host[+host]]
+A client referencing the export point will be directed to choose from
+the given list an alternative location for the filesystem.
+(Note that the server must have a mountpoint here, though a different
+filesystem is not required; so, for example,
+.IR "mount --bind" " /path /path"
+is sufficient.)
+.TP
+.IR replicas= path@host[+host][:path@host[+host]]
+If the client asks for alternative locations for the export point, it
+will be given this list of alternatives. (Note that actual replication
+of the filesystem must be handled elsewhere.)
+
+.TP
+.IR refer= path@host[+host][:path@host[+host]]
+A client referencing the export point will be directed to choose from
+the given list an alternative location for the filesystem.
+(Note that the server must have a mountpoint here, though a different
+filesystem is not required; so, for example,
+.IR "mount --bind" " /path /path"
+is sufficient.)
+.TP
+.IR replicas= path@host[+host][:path@host[+host]]
+If the client asks for alternative locations for the export point, it
+will be given this list of alternatives. (Note that actual replication
+of the filesystem must be handled elsewhere.)
.SS User ID Mapping
.PP
-.I nfsd
+.B nfsd
bases its access control to files on the server machine on the uid and
gid provided in each NFS RPC request. The normal behavior a user would
expect is that she can access her files on the server just as she would
.IR no_root_squash .
.PP
By default,
-'''.I nfsd
+'''.B nfsd
'''tries to obtain the anonymous uid and gid by looking up user
'''.I nobody
'''in the password file at startup time. If it isn't found, a uid and gid
-.I exportfs
+.B exportfs
chooses a uid and gid
of 65534 for squashed access. These values can also be overridden by
the
.IR anonuid " and " anongid
options.
'''.PP
-'''In addition to this,
-'''.I nfsd
+'''In addition to this,
+'''.B nfsd
'''lets you specify arbitrary uids and gids that should be mapped to user
'''nobody as well.
Finally, you can map all user requests to the
anonymous uid by specifying the
.IR all_squash " option.
-'''.PP
-'''For the benefit of installations where uids differ between different
-'''machines,
-'''.I nfsd
-'''provides several mechanism to dynamically map server uids to client
-'''uids and vice versa: static mapping files, NIS-based mapping, and
-'''.IR ugidd -based
-'''mapping.
-'''.PP
-'''.IR ugidd -based
-'''mapping is enabled with the
-'''.I map_daemon
-'''option, and uses the UGID RPC protocol. For this to work, you have to run
-'''the
-'''.IR ugidd (8)
-'''mapping daemon on the client host. It is the least secure of the three methods,
-'''because by running
-'''.IR ugidd ,
-'''everybody can query the client host for a list of valid user names. You
-'''can protect yourself by restricting access to
-'''.I ugidd
-'''to valid hosts only. This can be done by entering the list of valid
-'''hosts into the
-'''.I hosts.allow
-'''or
-'''.I hosts.deny
-'''file. The service name is
-'''.IR ugidd .
-'''For a description of the file's syntax, please read
-'''.IR hosts_access (5).
-'''.PP
-'''Static mapping is enabled by using the
-'''.I map_static
-'''option, which takes a file name as an argument that describes the mapping.
-'''NIS-based mapping queries the client's NIS server to obtain a mapping from
-'''user and group names on the server host to user and group names on the
-'''client.
.PP
Here's the complete list of mapping options:
.TP
Map requests from uid/gid 0 to the anonymous uid/gid. Note that this does
not apply to any other uids or gids that might be equally sensitive, such as
user
-.IR bin
+.IR bin
or group
.IR staff .
.TP
.IR no_root_squash
Turn off root squashing. This option is mainly useful for diskless clients.
-'''.TP
-'''.IR squash_uids " and " squash_gids
-'''This option specifies a list of uids or gids that should be subject to
-'''anonymous mapping. A valid list of ids looks like this:
-'''.IP
-'''.IR squash_uids=0-15,20,25-50
-'''.IP
-'''Usually, your squash lists will look a lot simpler.
.TP
.IR all_squash
Map all uids and gids to the anonymous user. Useful for NFS-exported
public FTP directories, news spool directories, etc. The opposite option
-is
+is
.IR no_all_squash ,
which is the default setting.
-'''.TP
-'''.IR map_daemon
-'''This option turns on dynamic uid/gid mapping. Each uid in an NFS request
-'''will be translated to the equivalent server uid, and each uid in an
-'''NFS reply will be mapped the other way round. This option requires that
-'''.IR rpc.ugidd (8)
-'''runs on the client host. The default setting is
-'''.IR map_identity ,
-'''which leaves all uids untouched. The normal squash options apply regardless
-'''of whether dynamic mapping is requested or not.
-'''.TP
-'''.IR map_static
-'''This option enables static mapping. It specifies the name of the file
-'''that describes the uid/gid mapping, e.g.
-'''.IP
-'''.IR map_static=/etc/nfs/foobar.map
-'''.IP
-'''The file's format looks like this
-'''.IP
-'''.nf
-'''.ta +3i
-'''# Mapping for client foobar:
-'''# remote local
-'''uid 0-99 - # squash these
-'''uid 100-500 1000 # map 100-500 to 1000-1400
-'''gid 0-49 - # squash these
-'''gid 50-100 700 # map 50-100 to 700-750
-'''.fi
-'''.TP
-'''.IR map_nis
-'''This option enables NIS-based uid/gid mapping. For instance, when
-'''the server encounters the uid 123 on the server, it will obtain the
-'''login name associated with it, and contact the NFS client's NIS server
-'''to obtain the uid the client associates with the name.
-'''.IP
-'''In order to do this, the NFS server must know the client's NIS domain.
-'''This is specified as an argument to the
-'''.I map_nis
-'''options, e.g.
-'''.IP
-'''.I map_nis=foo.com
-'''.IP
-'''Note that it may not be sufficient to simply specify the NIS domain
-'''here; you may have to take additional actions before
-'''.I nfsd
-'''is actually able to contact the server. If your distribution uses
-'''the NYS library, you can specify one or more NIS servers for the
-'''client's domain in
-'''.IR /etc/yp.conf .
-'''If you are using a different NIS library, you may have to obtain a
-'''special
-'''.IR ypbind (8)
-'''daemon that can be configured via
-'''.IR yp.conf .
.TP
.IR anonuid " and " anongid
These options explicitly set the uid and gid of the anonymous account.
/projects proj*.local.domain(rw)
/usr *.local.domain(ro) @trusted(rw)
/home/joe pc001(rw,all_squash,anonuid=150,anongid=100)
-/pub (ro,insecure,all_squash)
-/srv/www -sync,rw server @trusted @external(ro)
+/pub *(ro,insecure,all_squash)
+/srv/www \-sync,rw server @trusted @external(ro)
'''/pub/private (noaccess)
.fi
.PP
entry for the PC/NFS client discussed above. Line 5 exports the
public FTP directory to every host in the world, executing all requests
under the nobody account. The
-.I insecure
+.I insecure
option in this entry also allows clients with NFS implementations that
don't use a reserved port for NFS.
The sixth line exports a directory read-write to the machine 'server'
'''access to the private directory.
'''.SH CAVEATS
'''Unlike other NFS server implementations, this
-'''.I nfsd
+'''.B nfsd
'''allows you to export both a directory and a subdirectory thereof to
-'''the same host, for instance
+'''the same host, for instance
'''.IR /usr " and " /usr/X11R6 .
'''In this case, the mount options of the most specific entry apply. For
-'''instance, when a user on the client host accesses a file in
+'''instance, when a user on the client host accesses a file in
'''.IR /usr/X11R6 ,
-'''the mount options given in the
-'''.I /usr/X11R6
+'''the mount options given in the
+'''.I /usr/X11R6
'''entry apply. This is also true when the latter is a wildcard or netgroup
'''entry.
.SH FILES
.BR showmount (8).
'''.SH DIAGNOSTICS
'''An error parsing the file is reported using syslogd(8) as level NOTICE from
-'''a DAEMON whenever nfsd(8) or mountd(8) is started up. Any unknown
+'''a DAEMON whenever
+'''.BR nfsd (8)
+'''or
+'''.BR mountd (8)
+'''is started up. Any unknown
'''host is reported at that time, but often not all hosts are not yet known
-'''to named(8) at boot time, thus as hosts are found they are reported
-'''with the same syslogd(8) parameters.
+'''to
+'''.BR named (8)
+'''at boot time, thus as hosts are found they are reported
+'''with the same
+'''.BR syslogd (8)
+'''parameters.
projects / nfs-utils.git / blobdiff