Name

rmtab − table of local file systems mounted by remote NFS clients

Description

The rmtab file resides in the /etc directory and contains a list of all remote hosts that have mounted local file systems using the NFS protocols. Whenever a client performs a remote mount, the server machine’s mount daemon makes an entry in the server machine’s rmtab file. The umount command instructs the server’s mount daemon to remove the entry. The nfs_umount −b command broadcasts to all servers and informs them that they should remove all entries from rmtab created by the sender of the broadcast message. By placing a nfs_umount −b command in /etc/rc.local, rmtab tables on NFS servers can be purged of entries made by a crashed client, who, upon rebooting, did not remount the same file systems that it had before the system crashed.  The rmtab file is a series of lines of the form:

hostname:directory

Rather than rewrite the rmtab file on each umount request, the mount daemon comments out unmounted entries by placing a number sign (#) in the first character position of the appropriate line. The mount daemon rewrites the entire file, without commented out entries, no more frequently than every 30 minutes.  The frequency depends on the occurrence of umount requests.

This table is used only to preserve information between crashes and is read only by mountd() when it starts up. The mountd daemon keeps an in-core table, which it uses to handle requests from programs like showmount() and shutdown(.).

Restrictions

Although the rmtab table is close to the truth, it may contain erroneous information if NFS client machines fail to execute umount −a when they reboot. 

Files

/etc/rmtab

See Also

mount(8nfs), umount(8nfs), mountd(8nfs), showmount(8nfs), shutdown(8)