How to Dismount a Mounted File System

Novell Cool Solutions: Tip
By Curtis Parker

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Posted: 13 Dec 2004

Problem:

Unable to dismount a mounted file system while it is in use. Let's say you have mounted a network volume, cdrom, or a flash drive and now you want to dismount it but Linux won't allow it because the device is busy.

Solution:

First you will need to find out what process is using the mounted path. This can be done with the following command:
```
/usr/sbin/lsof +D /mnt/mounted_path
```
This command searches the mounted path for open files. If this is a mount for a large server volume, it will take some time to complete. It displays the command, PID, user, file name, etc for each open file.

Example:

You have mounted a usb flash drive at /mnt/usb using the command:
```
mount -t vfat /dev/sda1 /mnt/usb
```
You've done some work on the drive and then try to dismount the flash drive using the commmand:
```
umount /mnt/usb
```

It returns this output:

umount: /mnt/usb: device is busy
umount: /mnt/usb: device is busy

You must have some process running somewhere that is using that device, run this command:
```
/usr/sbin/lsof +D /mnt/usb
```

The output might look like this:

COMMAND	PID	USER	FD	TYPE	DEVICE	SIZE	NODE	NAME
bash	5308	root	cwd	DIR	8,1	16384	1	/mnt/usb
vi	5555	root	cwd	DIR	8,1	16384	1	/mnt/usb
vi	5555	root	5u	REG	8,1	12288	26928	/mnt/usb/.testfile.txt.swp

This shows that you have a terminal window running the bash shell that has changed its working directory to the usb flash drive and you have an instance of vi with testfile.txt open. Exit vi and "cd" out of the usb drive or close the terminal window. After doing so, when you re-run the lsof command, it shows no output. Re-run the umount command and it will return no errors.