COTD: fuser - identify processes using files or sockets

Today’s Command Of The Day is the “fuser” command.

Have you ever wanted to unmounted an NFS share, or local filesystem and couldn’t because it was in use?  The same applies to CD/DVD’s, PenDrives, etc.  Generally, you receive a message similar to the following:

# umount /dev/sdc1
umount: /media/disk: device is busy.

The fuser has many options.  The ones I use the most are “-cu”.  The “u” option appends the username to the PID and the “c” option is the same as the “m” option, is what you use if you are telling it to check a file, filesystem, or mounted device.

# fuser -cu /dev/sdc1
/dev/sdc1:            8500c(gsmeiers)

# ps  u -p 8500
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
gsmeiers  8500  0.0  0.2  21588  4488 pts/3    Ss+  08:25   0:00 bash

Here we see that /dev/sdc1 has one PID that is using it.  A further ps shows what that PID is.  You can specify either a device name or filesystem when using cu and it will work the same.

You can also, in some versions of fuser, specify a “-v” option to have it show the information about the processes it finds.   For example:

$ fuser -cv /dev/sdc1
USER        PID ACCESS COMMAND
/dev/sdc1:           gsmeiers   7367 ..c.. bash
gsmeiers   8500 ..c.. bash
gsmeiers   9534 F.c.. vi

Fuser also has other commands — such as the “-k” command, which can kill all processes that are using a particular filesystem/device.  Be careful with this one!

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This entry was written by theunixguy, posted on April 20, 2009 at 7:44 am, and filed under COTD and tagged , , .

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