The exportfs Command
Every file system being exported to remote users via NFS, as well as the access level for those file systems, are listed in the /etc/exports file. When the nfs service starts, the /usr/sbin/exportfs command launches and reads this file, and passes to rpc.mountd and rpc.nfsd the file systems available to remote users.
When issued manually, the /usr/sbin/exportfs command allows the root user to selectively export or unexport directories without restarting the NFS service. When passed the proper options, the /usr/sbin/exportfs command writes the exported file systems to /var/lib/nfs/xtab. Since rpc.mountd refers to the xtab file when deciding access privileges to a file system, changes to the list of exported file systems take effect immediately.
The following is a list of commonly used options available for /usr/sbin/exportfs:
- -r — Causes all directories listed in /etc/exports to be exported by constructing a new export list in /etc/lib/nfs/xtab. This option effectively refreshes the export list with any changes that have been made to /etc/exports.
- -a — Causes all directories to be exported or unexported, depending on what other options are passed to /usr/sbin/exportfs. If no other options are specified, /usr/sbin/exportfs exports all file systems specified in /etc/exports.
- -o file-systems — Specifies directories to be exported that are not listed in /etc/exports. Replace file-systems with additional file systems to be exported. These file systems must be formatted the same way they are specified in /etc/exports. Refer to Section 9.3.1 NFS Server Configuration File for more information on /etc/exports syntax. This option is often used to test an exported file system before adding it permanently to the list of file systems to be exported.
- -i — Ignores /etc/exports; only options given from the command line are used to define exported file systems.
- -u — Unexports all shared directories. The command /usr/sbin/exportfs -ua suspends NFS file sharing while keeping all NFS daemons up. To reenable NFS sharing, type exportfs -r.
- -v — Verbose operation, where the file systems being exported or unexported are displayed in greater detail when the exportfs command is executed.
If no options are passed to the /usr/sbin/exportfs command, it displays a list of currently exported file systems.