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
/usr/sbin/exportfs -s
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 and files under /etc/exports.d by invoking exportfs -a. However, a system administrator can choose to add or delete exports without modifying /etc/exports or files under /etc/exports.d 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 kernel, 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 table, 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 kernel's export table.
Options
- -d kind or --debug kind
Turn on debugging. Valid kinds are: all, auth, call, general and parse. Debugging can also be turned on by setting debug= in the [exportfs] section of /etc/nfs.conf.
- -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 and files under /etc/exports.d directory. Only default options and options given on the command line are used.
- -r
Reexport all directories, synchronizing /var/lib/nfs/etab with /etc/exports and files under /etc/exports.d. This option removes entries in /var/lib/nfs/etab which have been deleted from /etc/exports or files under /etc/exports.d, 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 kernel's export table by rpc.mountd when they make their next NFS mount request.
- -v
Be verbose. When exporting or unexporting, show what's going on. When displaying the current export list, also display the list of export options.
- -s
Display the current export list suitable for /etc/exports.
Configuration File
The [exportfs] section of the /etc/nfs.conf configuration file can contain a debug value, which can be one or more from the list general, call, auth, parse, all. When a list is given, the members should be comma-separated.
exportfs will also recognize the state-directory-path value from the [mountd] section.
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 and files under /etc/exports.d are added to /var/lib/nfs/etab. The kernel's 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 formats.
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 brackets. For IPv6 network addresses, place the prefix just after the closing 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 or files under /etc/exports.d.
A system administrator may override options from these sources using the -o command-line option on exportfs. This option takes a comma-separated 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 unexport a currently exported directory. 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 specified 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 and files under /etc/exports.d to /var/lib/nfs/etab and pushes the resulting export entries into the kernel:
# 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 and files under /etc/exports.d:
# 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 members 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
- /etc/exports.d
directory where extra input files are stored. Note: only files that end with .exports are used.
- /var/lib/nfs/etab
master table of exports
- /var/lib/nfs/rmtab
table of clients accessing server's exports
See Also
Referenced By
exports(5), mountd(8), nfs.conf(5), nfsconf(8), nfsd(7), nfsd(8).