Linux – Find what is Preventing You from Unmounting a Drive

Disclaimer: I’ve had this problem for probably four months, ever since I started running Plex Media Server on my headless linux machine at home, whilst storing all my actual media on a nice external portable drive. Usually I just yank it, but then I watch the drive letters run themselves up obscenely high before I need to reboot.

So you’ve gone through the process of mounting your drive in Linux:

> sudo fdisk -l
Device Boot = /dev/sdb1 (and a bunch of other technical information regarding drive size, id, and such)
> sudo mount -t ntfs-3g /dev/sdb1 /media/TOSHIBA

You run a bunch of stuff, get it all working, then find you need to take the drive to work the next day, so you try to unmount it.

> sudo umount /media/TOSHIBA
umount: /media/TOSHIBA: device is busy.
(In some cases useful info about processes that use the device is found by lsof(8) or fuser(1))