funmount(8)

funmount8

Forcibly unmount a file system

Usage

funmount path

Overview

funmount forcibly attempts to unmount the file system mounted on path. It is roughly equivalent to running umount -f path. However, on most operating systems the umount command does a great deal more than simply execute the unmount system call--for instance it may attempt to read the attributes of the file system being unmounted and/or contact a remote NFS server to notify it of the unmount operation. These extra actions make umount hang when a remote NFS server is unavailable or a loopback server has crashed, which in turn causes the client to become ever more wedged. funmount can avoid such situations when you are trying to salvage a machine with bad NFS mounts without rebooting it.

Caveats

SFS will get very confused if you ever unmount file systems from beneath it. SFS's nfsmounter program tries to clean up the mess if the client software ever crashes. Running funmount will generally only make things worse by confusing nfsmounter.

Releases

3 releases since Debian 3.0 (Woody); the text changed 2 times.

  1. 3.0
  2. 3.1
  3. 4.0

Bugs

If /a is a mount point, and /a/b is another mount point, unmounting /a before /a/b will cause the latter file system to become ``lost.'' Once a file system is lost, there is no way to unmount it without rebooting. Worse yet, on some operating systems, commands such as df may hang because of a lost file system.

Many operating systems will not let you unmount a file system (even forcibly) if a process is using the file system's root directory (for instance as a current working directory). Under such circumstances, funmount may fail. To unmount the file system you must find and kill whatever process is using the directory. Utilities such as fstat and lsof may be helpful for identifying processes with a particular file system open.

Author

[email protected]

From sfs-server 1:0.8-0+pre20060720.1-1 in Debian 4.0 (Etch). Parsed by carta from the page's man source.