NAME exportfs - maintain table of exported NFS file systems
SYNOPSIS /usr/sbin/exportfs [-avi] [-o options,..] [client:/path ..] /usr/sbin/exportfs -r [-v] /usr/sbin/exportfs [-av] -u [client:/path ..] /usr/sbin/exportfs [-v] /usr/sbin/exportfs -f
DESCRIPTION An NFS server maintains a table of local physical file systems that are accessible to NFS clients. Each file system in this table is referred to as an exported file system, or export, for short.
The exportfs command maintains the current table of exports for the NFS server. The master export table is kept in a file named /var/lib/nfs/etab. This file is read by rpc.mountd when a client sends an NFS MOUNT request.
Normally the master export table is initialized with the contents of /etc/exports by invoking exportfs -a. However, a system administrator can choose to add or delete exports without modifying /etc/exports by using the exportfs command.
exportfs and its partner program rpc.mountd work in one of two modes: a legacy mode which applies to 2.4 and earlier versions of the Linux ker- nel, and a new mode which applies to 2.6 and later versions, providing the nfsd virtual filesystem has been mounted at /proc/fs/nfsd or /proc/fs/nfs. On 2.6 kernels, if this filesystem is not mounted, the legacy mode is used.
In the new mode, exportfs does not give any information to the kernel, but provides it only to rpc.mountd through the /var/lib/nfs/etab file. rpc.mountd then manages kernel requests for information about exports, as needed.
In the legacy mode, exports which identify a specific host, rather than a subnet or netgroup, are entered directly into the kernel s export ta- ble, as well as being written to /var/lib/nfs/etab. Further, exports listed in /var/lib/nfs/rmtab which match a non host-specific export request will cause an appropriate export entry for the host given in rmtab to be added to the kernels export table.
OPTIONS -a Export or unexport all directories.
-o options,... Specify a list of export options in the same manner as in exports(5).
-i Ignore the /etc/exports file. Only default options and options given on the command line are used.
-r Reexport all directories, synchronizing /var/lib/nfs/etab with /etc/exports. This option removes entries in /var/lib/nfs/etab which have been deleted from /etc/exports, and removes any entries from the kernel export table which are no longer valid.
-u Unexport one or more directories.
-f If /proc/fs/nfsd or /proc/fs/nfs is mounted, flush everything out of the kernel s export table. Fresh entries for active clients are added to the kernels export table by rpc.mountd when they make their next NFS mount request.
-v Be verbose. When exporting or unexporting, show whats going on. When displaying the current export list, also display the list of export options.
DISCUSSION Exporting Directories The first synopsis shows how to invoke exportfs when adding new entries to the export table. When using exportfs -a, all exports listed in /etc/exports are added to /var/lib/nfs/etab. The kernels export table is also updated as needed.
The host:/path argument specifies a local directory to export, along with the client or clients who are permitted to access it. See exports(5) for a description of supported options and access list for- mats.
IPv6 presentation addresses contain colons, which are already used to separate the "host" and "path" command line arguments. When specifying a client using a raw IPv6 address, enclose the address in square brack- ets. For IPv6 network addresses, place the prefix just after the clos- ing bracket.
To export a directory to the world, simply specify :/path.
The export options for a particular host/directory pair derive from several sources. The default export options are sync,ro,root_squash,wdelay. These can be overridden by entries in /etc/exports.
A system administrator may override options from these sources using the -o command-line option on exportfs. This option takes a comma-sep- arated list of options in the same fashion as one would specify them in /etc/exports. In this way exportfs can be used to modify the export options of an already exported directory.
Unexporting Directories The third synopsis shows how to unexported a currently exported direc- tory. When using exportfs -ua, all entries listed in /var/lib/nfs/etab are removed from the kernel export tables, and the file is cleared. This effectively shuts down all NFS activity.
To remove an export, specify a host:/path pair. This deletes the speci- fied entry from /var/lib/nfs/etab and removes the corresponding kernel entry (if any).
Dumping the Export Table Invoking exportfs without options shows the current list of exported file systems. Adding the -v option causes exportfs to display the export options for each export.
EXAMPLES The following adds all directories listed in /etc/exports to /var/lib/nfs/etab and pushes the resulting export entries into the ker- nel:
# exportfs -a
To export the /usr/tmp directory to host django, allowing insecure file locking requests from clients:
# exportfs -o insecure_locks django:/usr/tmp
To unexport the /usr/tmp directory:
# exportfs -u django:/usr/tmp
To unexport all exports listed in /etc/exports:
# exportfs -au
To export the /usr/tmp directory to IPv6 link-local clients:
# exportfs [fe80::]/64:/usr/tmp
USAGE NOTES Exporting to IP networks or DNS and NIS domains does not enable clients from these groups to access NFS immediately. Rather, these sorts of exports are hints to rpc.mountd(8) to grant any mount requests from these clients. This is usually not a problem, because any existing mounts are preserved in rmtab across reboots.
When unexporting a network or domain entry, any current exports to mem- bers of this group will be checked against the remaining valid exports and if they themselves are no longer valid they will be removed.
FILES /etc/exports input file listing exports, export options, and access control lists
/var/lib/nfs/etab master table of exports
/var/lib/nfs/rmtab table of clients accessing server s exports
SEE ALSO exports(5), rpc.mountd(8), netgroup(5)
AUTHORS Olaf Kirch <firstname.lastname@example.org> Neil Brown <email@example.com>
31 December 2009 exportfs(8)