The umount command can be used to temporarily unmount a directory from a partition. For example, let's say the df -Th command shows that the /var directory is mounted onto the /dev/sda3 partition.
Filesystem Type Size Used Avail Use% Mounted on /dev/sda3 ext4 922M 90M 770M 11% /var
Likewise, the mount command will show that the /var directory is mounted onto the /dev/sda3 partition.
/dev/sda3 on /var type ext4 (rw,relatime,seclabel)
While mounted, you can view the contents of the /var directory.
~]# ll /var drwxr-xr-x. 9 root root 4096 May 14 15:54 log drwxr-xr-x. 9 root root 4096 May 14 15:54 logs drwx------. 2 root root 16384 May 14 15:47 lost+found drwxrwxrwt. 9 root root 4096 May 14 15:55 tmp
The umount command can be used to temporarily unmount the /var directory from the /dev/sda3 partition.
When attempting the unmount, if target is busy is displayed, the -l or --lazy flag can be used.
umount --lazy /var
Once unmounted, the /dev/sda3 parition will no longer be included in the df -Th command or in the mount command. Likewise, when attempting to view the contents of the /var directory, the following should be returned.
[root@lab1 ~]# ll /var total 0
The mount command can be used to remount the /var directory onto /dev/sda3.
mount -t ext4 /dev/sda3 /var
Or, if the /etc/fstab file is configured to mount the /var directory to the /dev/sda3 parition at boot, restarting the system should mount the /var directory onto the /dev/sda3 parition.
UUID=7a8e7883-e6ee-4482-a7ca-665bfe94eaa8 /var ext4 defaults 1 2