-.TH EXPORTS 5 "28 October 1999"
-.UC 5
+.TH EXPORTS 5 "4 March 2005" "Linux" "Linux File Formats Manual"
.SH NAME
exports \- NFS file systems being exported (for Kernel based NFS)
.SH SYNOPSIS
list of export options for that client. No whitespace is permitted
between a client and its option list.
.PP
+Also, each line may have one or more specifications for default options
+after the path name, in the form of a dash ("\-") followed by an option
+list. The option list is used for all subsequent exports on that line
+only.
+.PP
Blank lines are ignored. A pound sign ("#") introduces a comment to the
end of the line. Entries may be continued across newlines using a
backslash. If an export name contains spaces it should be quoted using
the export name using a backslash followed by the character code as three
octal digits.
.PP
+To apply changes to this file, run 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
'''.B \-\-public\-root
'''option. Multiple specifications of a public root will be ignored.
.PP
+.SS RPCSEC_GSS security
+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
understands the following export options:
.TP
.IR secure "\*d
-This option requires that requests originate on an internet port less
+This option requires that requests originate on an Internet port less
than IPPORT_RESERVED (1024). This option is on by default. To turn it
off, specify
.IR insecure .
an unclean server restart (i.e. a crash) can cause data to be lost or
corrupted.
-In releases of nfs-utils upto and including 1.0.0, this option was the
-default. In this and future releases,
+.TP
+.IR sync
+Reply to requests only after the changes have been committed to stable
+storage (see
+.IR async
+above).
+
+In releases of nfs-utils up to and including 1.0.0, this option was the
+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 adminstrators aware of this change, 'exportfs'
+must be explicitly requested if needed.
+To help make system administrators aware of this change, 'exportfs'
will issue a warning if neither
.I sync
nor
The option can be explicitly disabled with
.IR hide .
.TP
+.IR crossmnt
+This option is similar to
+.I nohide
+but it makes it possible for clients to move from the filesystem marked
+with crossmnt to exported filesystems mounted on it. Thus when a child
+filesystem "B" is mounted on a parent "A", setting crossmnt on "A" has
+the same effect as setting "nohide" on B.
+.TP
.IR no_subtree_check
This option disables subtree checking, which has mild security
-implications, but can improve reliability is some circumstances.
+implications, but can improve reliability in some circumstances.
If a subdirectory of a filesystem is exported, but the whole
filesystem isn't then whenever a NFS request arrives, the server must
directories to which only root has access can only be accessed if the
filesystem is exported with
.I no_root_squash
-(see below), even the file itself allows more general access.
+(see below), even if the file itself allows more general access.
As a general guide, a home directory filesystem, which is normally
exported at the root and may see lots of file renames, should be
requested with
.IR subtree_check .
+From release 1.1.0 of nfs-utils onwards, the default will be
+.I no_subtree_check
+as subtree_checking tends to cause more problems than it is worth.
+If you genuinely require subtree checking, you should explicitly put
+that option in the
+.B exports
+file. If you put neither option,
+.I exportfs
+will warn you that the change is pending.
+
.TP
.IR insecure_locks
.TP
.IR auth_nlm ,
or
.IR secure_locks .
+.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
+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
+NFSv3 clients use the ACCESS RPC to perform all access decisions on
+the server. Note that the
+.I no_acl
+option only has effect on kernels specially patched to support it, and
+when exporting filesystems with ACL support. The default is to export
+with ACL support (i.e. by default,
+.I no_acl
+is off).
'''.TP
'''.I noaccess
'''.TP
'''.IR link_absolute
'''Leave all symbolic link as they are. This is the default operation.
+
+.TP
+.IR mountpoint= path
+.TP
+.I mp
+This option makes it possible to only export a directory if it has
+successfully been mounted.
+If no path is given (e.g.
+.IR mountpoint " or " mp )
+then the export point must also be a mount point. If it isn't then
+the export point is not exported. This allows you to be sure that the
+directory underneath a mountpoint will never be exported by accident
+if, for example, the filesystem failed to mount due to a disc error.
+
+If a path is given (e.g.
+.IR mountpoint= "/path or " mp= /path)
+then the nominated path must be a mountpoint for the exportpoint to be
+exported.
+
+.TP
+.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.
+
+Other filesystems can be identified with a small integer, or a UUID
+which should contain 32 hex digits and arbitrary punctuation.
+
+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.
+
+.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
'''in the password file at startup time. If it isn't found, a uid and gid
.I exportfs
chooses a uid and gid
-of -2 (i.e. 65534) for squashed access. These values can also be overridden by
+of 65534 for squashed access. These values can also be overridden by
the
.IR anonuid " and " anongid
options.
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
.IR root_squash
Map requests from uid/gid 0 to the anonymous uid/gid. Note that this does
-not apply to any other uids that might be equally sensitive, such as user
-.IR bin .
+not apply to any other uids or gids that might be equally sensitive, such as
+user
+.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
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)
+/pub *(ro,insecure,all_squash)
+/srv/www \-sync,rw server @trusted @external(ro)
'''/pub/private (noaccess)
.fi
.PP
.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'
+as well as the `@trusted' netgroup, and read-only to netgroup `@external',
+all three mounts with the `sync' option enabled.
''' The last line denies all NFS clients
'''access to the private directory.
'''.SH CAVEATS
'''entry.
.SH FILES
/etc/exports
+.SH SEE ALSO
+.BR exportfs (8),
+.BR netgroup (5),
+.BR mountd (8),
+.BR nfsd (8),
+.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
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