To access a file system's contents, you must attach its block device to a mount point in the directory hierarchy. You can use the mkdir command to create a directory for use as a mount point, for example:

# mkdir /var/projects

You can use an existing directory as a mount point, but its contents are hidden until you unmount the overlying file system.

The mount command attaches the device containing the file system to the mount point:

# mount [options] device mount_point

You can specify the device by its name, UUID, or label. For example, the following commands are equivalent ways of mounting the file system on the block device /dev/sdb1:

# mount /dev/sdb1 /var/projects
# mount UUID="ad8113d7-b279-4da8-b6e4-cfba045f66ff" /var/projects
# mount LABEL="Projects" /var/projects

If you do not specify any arguments, mount displays all file systems that the system currently has mounted, for example:

# mount
/dev/mapper/vg_host01-lv_root on / type ext4 (rw)
...

In this example, the LVM logical volume /dev/mapper/vg_host01-lv_root is mounted on /. The file system type is ext4 and is mounted for both reading and writing. (You can also use the command cat /proc/mounts to display information about mounted file systems.)

The df command displays information about home much space remains on mounted file systems, for example:

# df -h
Filesystem                     Size  Used Avail Use% Mounted on
/dev/mapper/vg_host01-lv_root  36G   12G   22G  36% /
...

You can use the -B (bind) option to the mount command to attach a block device at multiple mount points. You can also remount part of a directory hierarchy, which need not be a complete file system, somewhere else. For example, the following command mounts /var/projects/project1 on /mnt:

# mount -B /var/projects/project1 /mnt

Each directory hierarchy acts as a mirror of the other. The same files are accessible in either location, although any submounts are not replicated. These mirrors do not provide data redundancy.

You can also mount a file over another file, for example:

# touch /mnt/foo
# mount -B /etc/hosts /mnt/foo

In this example, /etc/hosts and /mnt/foo represent the same file. The existing file that acts as a mount point is not accessible until you unmount the overlying file.

The -B option does not recursively attach any submounts below a directory hierarchy. To include submounts in the mirror, use the -R (recursive bind) option instead.

When you use -B or -R, the file system mount options remain the same as those for the original mount point. To modify, the mount options, use a separate remount command, for example:

# mount -o remount,ro /mnt/foo

You can mark the submounts below a mount point as being shared, private, or slave:

To prevent a mount from being mirrored by using the -B or -R options, mark its mount point as being unbindable:

# mount --make-unbindable mount_point

To move a mounted file system, directory hierarchy, or file between mount points, use the -M option, for example:

# touch /mnt/foo
# mount -M /mnt/foo /mnt/bar

To unmount a file system, use the umount command, for example:

# umount /var/projects

Alternatively, you can specify the block device provided that it is mounted on only one mount point.

For more information, see the mount(8) and umount(8) manual pages.