[Solved] Cannot unmount: device is busy

[Luc484]

Hi all. It's been some days since I started to have this problem. When I try to unmount a partition (dvd) I get:

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pluca luca # umount /dev/hdc
umount: /mnt/cdrom: device is busy
umount: /mnt/cdrom: device is busy

I know it's quite usual, and it means some process is still using the device, right? So, as usual, I try to find the process with:

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fuser -u /dev/hdc

but, strangely I get no process. I used to have some process using the resource, but not this time. I get nothing. But umount still says the device is in use. I've never had this problem before. Any idea?
Thanks for any help, it's not too good to restart each time I unmount the volume.

[Row]

This problem is so typical... It usually occurs when:

a) A process is accesing the device, solution: just close the app
b) A process is working even offline with the device (i.e., you have the device content or content of a folder of the device shown on your filemanager): just move to another folder or close the filemanager
c) A process was working with the app, got closed but freed incorrectly its file descriptors, so there is no process anywhere but kernel still keeps a file descriptor pointing to the device. Solution: just pray. In fact, I don't know any way to fix this but rebooting.

Bye!

[Luc484]

c) A process was working with the app, got closed but freed incorrectly its file descriptors, so there is no process anywhere but kernel still keeps a file descriptor pointing to the device. Solution: just pray. In fact, I don't know any way to fix this but rebooting.

I'm surely in this case. Strange that I haven't seen this for years and now I see it so often.
Thanks for your answer.

[SZwarts]

You can also use the command eject if you have that installed. You can call eject with as a parameter the mount point or the device, it will unmount stuff itself for you, if that can be 'easily' done.

[vadik56]

You can unmount with -l "lazy" option that way you can at least remove your dvd:

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umount -l /dev/dvd

[Aysen]

You can unmount with -l "lazy" option that way you can at least remove your dvd:

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umount -l /dev/dvd

True.
It also helps me when sometimes my USB stick gets "stuck" the way Luc484 described.

[Luc484]

I discovered the problem was mainly caused by NFS. Even if I unmount the device from the system connecting through NFS, the device is used since it is exported. I have to stop NFS to unmount the device locally. It seems not comfortable like this to me, but I read it is normal.
Thanks for your suggestions.

[mattmatteh]

the only option is to reboot ? i was working on an install and could not umount /mnt/gentoo/dev

logger ~ # umount /mnt/gentoo/dev
umount: /mnt/gentoo/dev: device is busy
umount: /mnt/gentoo/dev: device is busy
logger ~ # lsof | grep 'mnt/gentoo/dev'
udevd 11601 root 0u CHR 1,3 983 /mnt/gentoo/dev/null
udevd 11601 root 1u CHR 1,3 983 /mnt/gentoo/dev/null
udevd 11601 root 2u CHR 1,3 983 /mnt/gentoo/dev/null
logger ~ #

rebooting is a windows solution. is there a bug to be filed ?

i have another box like this too where i need it un mounted but can not reboot.

anyone have a solution to this ?

matt

[Luc484]

the only option is to reboot ? i was working on an install and could not umount /mnt/gentoo/dev

logger ~ # umount /mnt/gentoo/dev
umount: /mnt/gentoo/dev: device is busy
umount: /mnt/gentoo/dev: device is busy
logger ~ # lsof | grep 'mnt/gentoo/dev'
udevd 11601 root 0u CHR 1,3 983 /mnt/gentoo/dev/null
udevd 11601 root 1u CHR 1,3 983 /mnt/gentoo/dev/null
udevd 11601 root 2u CHR 1,3 983 /mnt/gentoo/dev/null
logger ~ #

rebooting is a windows solution. is there a bug to be filed ?

i have another box like this too where i need it un mounted but can not reboot.

anyone have a solution to this ?

matt

I don't know whether this is the same problem I had or not. Anyway, in my case it is not necessary to reboot the system. It is only necessary to restart NFS on the client machine. That's it.
I googled a little bit and found out this is a common behaviour and it seems it is not considered a bug. I don't know if this is your case or not.

[mattmatteh]

i didnt have any nfs mounts. i was thinking this might be a the problem, but thats only a guess.

c) A process was working with the app, got closed but freed incorrectly its file descriptors, so there is no process anywhere but kernel still keeps a file descriptor pointing to the device. Solution: just pray. In fact, I don't know any way to fix this but rebooting.

matt

[loony]

c) A process was working with the app, got closed but freed incorrectly its file descriptors, so there is no process anywhere but kernel still keeps a file descriptor pointing to the device. Solution: just pray. In fact, I don't know any way to fix this but rebooting.

Thank you so much, I almost got crazy about this fuser, lsof, ps etc and I couldn't get any info which process sits on that path. Also, the umount -l command helped me out with this.

loony

[x22]

c) A process was working with the app, got closed but freed incorrectly its file descriptors, so there is no process anywhere but kernel still keeps a file descriptor pointing to the device. Solution: just pray. In fact, I don't know any way to fix this but rebooting.

Kernel will always close files open by a process before completely destroying it.

But kernel may have files open for its own purposes (swap, loopback devices, mounting filesystems, NFS, ...) and this use is invisible for lsof and fuser.