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9.3.2. 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/exportsfile. When the
nfsservice starts, the
/usr/sbin/exportfscommand launches and reads this file, passes control to
rpc.mountd(if NFSv2 or NFSv3) for the actual mounting process, then to
rpc.nfsdwhere the file systems are then available to remote users.
When issued manually, the
/usr/sbin/exportfscommand allows the root user to selectively export or unexport directories without restarting the NFS service. When given the proper options, the
/usr/sbin/exportfscommand writes the exported file systems to
rpc.mountdrefers to the
xtabfile 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
-r— Causes all directories listed in
/etc/exportsto 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
-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/exportfsexports all file systems specified in
-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 in the same way they are specified in
/etc/exports. Refer to Section 9.3.1, “The
/etc/exportsConfiguration File” for more information on
/etc/exportssyntax. This option is often used to test an exported file system before adding it permanently to the list of file systems to be exported.
/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 -uasuspends NFS file sharing while keeping all NFS daemons up. To re-enable NFS sharing, type
-v— Verbose operation, where the file systems being exported or unexported are displayed in greater detail when the
exportfscommand is executed.
If no options are passed to the
/usr/sbin/exportfscommand, it displays a list of currently exported file systems.
For more information about the
/usr/sbin/exportfscommand, refer to the
exportfs with NFSv4
Since NFSv4 no longer utilizes the
rpc.mountdprotocol as was used in NFSv2 and NFSv3, the mounting of file systems has changed.
An NFSv4 client now has the ability to see all of the exports served by the NFSv4 server as a single file system, called the NFSv4 pseudo-file system. On Red Hat Enterprise Linux, the pseudo-file system is identified as a single, real file system, identified at export with the
For example, the following commands could be executed on an NFSv4 server:
mkdir /exports mkdir /exports/opt mkdir /exports/etc mount --bind /usr/local/opt /exports/opt mount --bind /usr/local/etc /exports/etc exportfs -o fsid=0,insecure,no_subtree_check gss/krb5p:/exports exportfs -o rw,nohide,insecure,no_subtree_check gss/krb5p:/exports/opt exportfs -o rw,nohide,insecure,no_subtree_check gss/krb5p:/exports/etc
In this example, clients are provided with multiple file systems to mount, by using the