Mount – umount: Device is Busy. Why?

mount

When running umount /path I get:

umount: /path: device is busy.

The filesystem is huge, so lsof +D /path is not a realistic option.

lsof /path, lsof +f -- /path, and fuser /path all return nothing. fuser -v /path gives:

                  USER        PID ACCESS COMMAND
/path:            root     kernel mount /path

which is normal for all unused mounted file systems.

umount -l and umount -f is not good enough for my situation.

How do I figure out why the kernel thinks this filesystem is busy?

Best Answer

It seems the cause for my issue was the nfs-kernel-server was exporting the directory. The nfs-kernel-server probably goes behind the normal open files and thus is not listed by lsof and fuser.

When I stopped the nfs-kernel-server I could umount the directory.

I have made a page with examples of all solutions so far here: http://oletange.blogspot.com/2012/04/umount-device-is-busy-why.html

Related Solutions

Umount – device is busy

It means that some process has a working directory or an open file handle underneath the mount point. The best thing to do is to end the offending process, change its working directory or close the file handle before unmounting.

There is an alternative on Linux though. Using umount -l calls a "lazy" unmount. The filesystem will still be mounted but you won't be able to see or use it, except for processes that are already using it. When the offending program exits (through whatever means) the system will "finish" unmounting the filesystem.

Linux – ‘user’ Option Works for Mount but Not for Umount

The problem is that your /etc/mtab is not a file but a symlink to /proc/mounts. This has advantages but also the disadvantage that user does not work. You already guessed right the reason for that: "the system is confused when remembering who mounted the file system". This information is written to mtab, cannot be written there in your case though. The kernel doesn't care (doesn't even know) about user mounts (this is a userspace feature). Thus this info is not contained in /proc/mounts.

Do this:

cd /etc
cp mtab mtab.file
rm mtab
mv mtab.file mtab

umount as user should work after you have mounted the volume again.

Best Answer

Related Solutions

Umount – device is busy

Linux – ‘user’ Option Works for Mount but Not for Umount

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