Unmounting a File System on Linux
Sometimes, you need to ensure that a disc is offline - for example, when running certain disc repair utilities, such as fschk or when replacing hardware. In these cases, it is important that no process (including the operating system itself) is accessing the drive at the same time.
The command to unmount a filesystem in Linux is:
umount <device name>
Note: that the command is umount and not unmount!
$ sudo umount /dev/sda
$ sudo umount /dev/sdb1
$ umount /media/myuser/PENDRIVE
You can verify the filesystem has been unmounted using the df command - and checking that it is no longer listed:
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda1 74866848 62937340 8126424 89% /
udev 1020744 4 1020740 1% /dev
tmpfs 411396 836 410560 1% /run
none 5120 0 5120 0% /run/lock
none 1028480 868 1027612 1% /run/shm
none 102400 60 102340 1% /run/user
/dev/sdb1 3909784 3481364 428420 90% /media/myuser/PENDRIVE
If you want to permanently unmount a filesystem (-for example, if the drive is being removed altogether) you will need to remove it from /etc/fstab. This is a text file used by Linux during system startup to tell what should be connected to the system. It can be edited via any text editor - for example:
sudo vi /etc/fstab
The file format is described in the section on Mounting a New File System, but it is simply a case of removing the line for the desired filesystem and saving the changes.
Once you have done this, the next time you boot Linux, that filesystem will no longer be mounted (-or accessible) - unless you manually mount it.
Note: that changes to /etc/fstab will only take effect once you reboot the system