-.TH EXPORTS 5 "11 August 1997"
-.UC 5
+.TH EXPORTS 5 "4 March 2005" "Linux" "Linux File Formats Manual"
.SH NAME
-exports \- NFS file systems being exported
+exports \- NFS file systems being exported (for Kernel based NFS)
.SH SYNOPSIS
.B /etc/exports
.SH DESCRIPTION
The file
.I /etc/exports
serves as the access control list for file systems which may be
-exported to NFS clients. It it used by both the NFS mount daemon,
+exported to NFS clients. It is used by
+.IR exportfs (8)
+to give information to
.IR mountd (8)
-and the NFS file server daemon
+and to the kernel based NFS file server daemon
.IR nfsd (8).
.PP
The file format is similar to the SunOS
.I exports
-file, except that several additional options are permitted. Each line
-contains a mount point and a list of machine or netgroup names allowed
-to mount the file system at that point. An optional parenthesized list
-of mount parameters may follow each machine name. Blank lines are
-ignored, and a # introduces a comment to the end of the line. Entries may
-be continued across newlines using a backslash.
+file. Each line contains an export point and a whitespace-separated list
+of clients allowed to mount the file system at that point. Each listed
+client may be immediately followed by a parenthesized, comma-separated
+list of export options for that client. No whitespace is permitted
+between a client and its option list.
+.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
+double quotes. You can also specify spaces or other unusual character in
+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 (on Debian)
+/etc/init.d/nfs-kernel-server reload.
.PP
.SS Machine Name Formats
NFS clients may be specified in a number of ways:
.IP "single host
This is the most common format. You may specify a host either by an
-abbreviated name recognizued be the resolver, the fully qualified domain
+abbreviated name recognized be the resolver, the fully qualified domain
name, or an IP address.
.IP "netgroups
NIS netgroups may be given as
.IR @group .
-Only the host part of all
-netgroup members is extracted and added to the access list. Empty host
+Only the host part of each
+netgroup members is consider in checking for membership. Empty host
parts or those containing a single dash (\-) are ignored.
.IP "wildcards
Machine names may contain the wildcard characters \fI*\fR and \fI?\fR.
This can be used to make the \fIexports\fR file more compact; for instance,
-\fI*.cs.foo.edu\fR matches all hosts in the domain \fIcs.foo.edu\fR. However,
-these wildcard characters do not match the dots in a domain name, so the
-above pattern does not include hosts such as \fIa.b.cs.foo.edu\fR.
+\fI*.cs.foo.edu\fR matches all hosts in the domain
+\fIcs.foo.edu\fR. As these characters also match the dots in a domain
+name, the given pattern will also match all hosts within any subdomain
+of \fIcs.foo.edu\fR.
.IP "IP networks
You can also export directories to all hosts on an IP (sub-) network
simultaneously. This is done by specifying an IP address and netmask pair
as
-.IR address/netmask .
-.TP
-.B =public
-This is a special ``hostname'' that identifies the given directory name
-as the public root directory (see the section on WebNFS in
-.BR nfsd (8)
-for a discussion of WebNFS and the public root handle). When using this
-convention,
-.B =public
-must be the only entry on this line, and must have no export options
-associated with it. Note that this does
-.I not
-actually export the named directory; you still have to set the exports
-options in a separate entry.
+.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
+may work by accident when reverse DNS lookups fail.
+'''.TP
+'''.B =public
+'''This is a special ``hostname'' that identifies the given directory name
+'''as the public root directory (see the section on WebNFS in
+'''.BR nfsd (8)
+'''for a discussion of WebNFS and the public root handle). When using this
+'''convention,
+'''.B =public
+'''must be the only entry on this line, and must have no export options
+'''associated with it. Note that this does
+'''.I not
+'''actually export the named directory; you still have to set the exports
+'''options in a separate entry.
+'''.PP
+'''The public root path can also be specified by invoking
+'''.I nfsd
+'''with the
+'''.B \-\-public\-root
+'''option. Multiple specifications of a public root will be ignored.
.PP
-The public root path can also be specified by invoking
-.I nfsd
-with the
-.B \-\-public\-root
-option. Multiple specifications of a public root will be ignored.
+.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.
.PP
.SS General Options
-.IR mountd " and " nfsd
-understand the following export options:
+.IR exportfs
+understands the following export options:
.TP
.IR secure "\*d
This option requires that requests originate on an internet port less
off, specify
.IR insecure .
.TP
-.IR ro
-Allow only read-only requests on this NFS volume. The default is to
-allow write requests as well, which can also be made explicit by using
+.IR rw
+Allow both read and write requests on this NFS volume. The
+default is to disallow any request which changes the filesystem.
+This can also be made explicit by using
the
-.IR rw " option.
+.IR ro " option.
+.TP
+.IR async
+This option allows the NFS server to violate the NFS protocol and
+reply to requests before any changes made by that request have been
+committed to stable storage (e.g. disc drive).
+
+Using this option usually improves performance, but at the cost that
+an unclean server restart (i.e. a crash) can cause data to be lost or
+corrupted.
+
+.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 upto and including 1.0.0, this option was the
+default. In this and future releases,
+.I sync
+is the default, and
+.I async
+must be explicit requested if needed.
+To help make system adminstrators aware of this change, 'exportfs'
+will issue a warning if neither
+.I sync
+nor
+.I async
+is specified.
+.TP
+.IR no_wdelay
+This option has no effect if
+.I async
+is also set. The NFS server will normally delay committing a write request
+to disc slightly if it suspects that another related write request may be in
+progress or may arrive soon. This allows multiple write requests to
+be committed to disc with the one operation which can improve
+performance. If an NFS server received mainly small unrelated
+requests, this behaviour could actually reduce performance, so
+.IR no_wdelay
+is available to turn it off.
+The default can be explicitly requested with the
+.IR wdelay " option.
+.TP
+.IR nohide
+This option is based on the option of the same name provided in IRIX
+NFS. Normally, if a server exports two filesystems one of which is
+mounted on the other, then the client will have to mount both
+filesystems explicitly to get access to them. If it just mounts the
+parent, it will see an empty directory at the place where the other
+filesystem is mounted. That filesystem is "hidden".
+
+Setting the
+.I nohide
+option on a filesystem causes it not to be hidden, and an
+appropriately authorised client will be able to move from the parent to
+that filesystem without noticing the change.
+
+However, some NFS clients do not cope well with this situation as, for
+instance, it is then possible for two files in the one apparent
+filesystem to have the same inode number.
+
+The
+.I nohide
+option is currently only effective on
+.I "single host
+exports. It does not work reliably with netgroup, subnet, or wildcard
+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
+copes with the situation effectively.
+
+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 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
+check not only that the accessed file is in the appropriate filesystem
+(which is easy) but also that it is in the exported tree (which is
+harder). This check is called the
+.IR subtree_check .
+
+In order to perform this check, the server must include some
+information about the location of the file in the "filehandle" that is
+given to the client. This can cause problems with accessing files that
+are renamed while a client has them open (though in many simple cases
+it will still work).
+
+subtree checking is also used to make sure that files inside
+directories to which only root has access can only be accessed if the
+filesystem is exported with
+.I no_root_squash
+(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
+exported with subtree checking disabled. A filesystem which is mostly
+readonly, and at least doesn't see many file renames (e.g. /usr or
+/var) and for which subdirectories may be exported, should probably be
+exported with subtree checks enabled.
+
+The default of having subtree checks enabled, can be explicitly
+requested with
+.IR subtree_check .
+
.TP
-.I noaccess
-This makes everything below the directory inaccessible for the named
-client. This is useful when you want to export a directory hierarchy to
-a client, but exclude certain subdirectories. The client's view of a
-directory flagged with noaccess is very limited; it is allowed to read
-its attributes, and lookup `.' and `..'. These are also the only entries
-returned by a readdir.
+.IR insecure_locks
.TP
-.IR link_relative
-Convert absolute symbolic links (where the link contents start with a
-slash) into relative links by prepending the necessary number of ../'s
-to get from the directory containing the link to the root on the
-server. This has subtle, perhaps questionable, semantics when the file
-hierarchy is not mounted at its root.
+.IR no_auth_nlm
+This option (the two names are synonymous) tells the NFS server not to require authentication of
+locking requests (i.e. requests which use the NLM protocol). Normally
+the NFS server will require a lock request to hold a credential for a
+user who has read access to the file. With this flag no access checks
+will be performed.
+
+Early NFS client implementations did not send credentials with lock
+requests, and many current NFS clients still exist which are based on
+the old implementations. Use this flag if you find that you can only
+lock files which are world readable.
+
+The default behaviour of requiring authentication for NLM requests can
+be explicitly requested with either of the synonymous
+.IR auth_nlm ,
+or
+.IR secure_locks .
.TP
-.IR link_absolute
-Leave all symbolic link as they are. This is the default operation.
+.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
+'''This makes everything below the directory inaccessible for the named
+'''client. This is useful when you want to export a directory hierarchy to
+'''a client, but exclude certain subdirectories. The client's view of a
+'''directory flagged with noaccess is very limited; it is allowed to read
+'''its attributes, and lookup `.' and `..'. These are also the only entries
+'''returned by a readdir.
+'''.TP
+'''.IR link_relative
+'''Convert absolute symbolic links (where the link contents start with a
+'''slash) into relative links by prepending the necessary number of ../'s
+'''to get from the directory containing the link to the root on the
+'''server. This has subtle, perhaps questionable, semantics when the file
+'''hierarchy is not mounted at its root.
+'''.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 nominted path must be a mountpoint for the exportpoint to be
+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.
+
+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.
+
+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).
+
+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.
+
.SS User ID Mapping
.PP
.I nfsd
.IR no_root_squash .
.PP
By default,
-.I 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
-of -2 (i.e. 65534) is used. These values can also be overridden by
+'''.I 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
+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
-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
+'''.PP
+'''In addition to this,
+'''.I 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
+'''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
.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 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 1000-1500
-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 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.
/usr *.local.domain(ro) @trusted(rw)
/home/joe pc001(rw,all_squash,anonuid=150,anongid=100)
/pub (ro,insecure,all_squash)
-/pub/private (noaccess)
+'''/pub/private (noaccess)
.fi
.PP
The first line exports the entire filesystem to machines master and trusty.
under the nobody account. The
.I insecure
option in this entry also allows clients with NFS implementations that
-don't use a reserved port for NFS. The last line denies all NFS clients
-access to the private directory.
-.SH CAVEATS
-Unlike other NFS server implementations, this
-.I nfsd
-allows you to export both a directory and a subdirectory thereof to
-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
-.IR /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.
+don't use a reserved port for NFS.
+''' The last line denies all NFS clients
+'''access to the private directory.
+'''.SH CAVEATS
+'''Unlike other NFS server implementations, this
+'''.I nfsd
+'''allows you to export both a directory and a subdirectory thereof to
+'''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
+'''.IR /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
/etc/exports
-.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
-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.
+.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
+'''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.
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