Forcefully unmount a linux disk partition

1. How do I forcefully unmount a Linux disk partition?
by nixcraft on January 27, 2006 · 6 comments
It happens many times you try to unmount a disk partition or mounted CD/DVD disk
and if you try to unmount device, which is accessed by other users, then you
will get error umount: /xxx: device is busy. However, Linux/FreeBSD comes with
fuser command to kill forcefully mounted partition.
Understanding device error busy error
What happens basically, is that Linux / UNIX will not allow you to unmount a
device that is busy. There are many reasons for this (such as program accessing
partition or open file) , but the most important one is to prevent data loss.
Try the following command to find out what processes have activities on the
device/partition. If your device name is /dev/sdb1, enter the following command
as root user:
# lsof | grep '/dev/sda1'
Output:
vi 4453 vivek 3u BLK 8,1 8167
/dev/sda1Above output tells that user vivek has a vi process running that is
using /dev/sda1. All you have to do is stop vi process and run umount again. As
soon as that program terminates its task, the device will no longer be busy and
you can unmount it with the following command:
# umount /dev/sda1
Following disussion allows you to unmout device and partition forcefully using
Linux commands.
Linux fuser command to forcefully unmount a disk partition
Suppose you have /dev/sda1 mounted on /mnt directory then you can use fuser
command as follows:
WARNING! These examples may result into data loss if not executed properly (see
"Understanding device error busy error" for more information).
Type the command to unmount /mnt forcefully:
# fuser -km /mnt
Where,
-k : Kill processes accessing the file.
-m : Name specifies a file on a mounted file system or a block device that is
mounted. In above example you are using /mnt
Linux umount command to unmount a disk partition
You can also try umount command with –l option:
# umount -l /mnt
Where,
-l : Also known as Lazy unmount. Detach the filesystem from the filesystem
hierarchy now, and cleanup all references to the filesystem as soon as it is not
busy anymore. This option works with kernel version 2.4.11+ and above only.
If you would like to unmount a NFS mount point then try following command:
# umount -f /mnt
Where,
-f: Force unmount in case of an unreachable NFS system
Caution: Using these commands or option can cause data loss for open files;
programs which access files after the file system has been unmounted will get an
error.