You use the mount command to attach the device containing the file system to the mount point as follows:

sudo mount [options] device mount_point

The device can be mounted by referencing its name, UUID, or label. For example, to mount the file system that was created in the previous section to /var/projects, any of the following commands can be used after you create the directory by running the following commands:

sudo mkdir /var/projects

sudo mount /dev/sdb1 /var/projects

sudo mount UUID="ad8113d7-b279-4da8-b6e4-cfba045f66ff" /var/projects

sudo mount LABEL="Projects" /var/projects

Issuing the mount command by itself displays all the mounted file systems. In the following example, an extract of the command's output indicates the following:

• /dev/sdb1 with an ext4 file system is mounted on /var/projects for both reading and writing

• /dev/mapper/vg_host01-lv_root, an LVM logical volume also with an ext4 file system, is mounted on / for both reading and writing:

sudo mount

The output of the previous command would be similar to the following:

/dev/sdb1 on /var/projects type ext4 (rw)
/dev/mapper/vg_host01-lv_root on / type ext4 (rw)
...

Or, you can use the cat /proc/mounts command to display information about mounted file systems.

The df -h command displays information about file systems and their use of disk space:

Filesystem      Size  Used Avail Use% Mounted on
...
/dev/sda3        46G   18G   29G  39% /
/dev/sda2       795M  452M  344M  57% /boot
/dev/sda1       100M  5.7M   95M   6% /boot/efi
...

To attach or bind a block device at several mount points, use the mount -B command.

You can also remount part of a directory hierarchy, which need not be a complete file system, somewhere else. For example, you would use the following command to mount /var/projects/project1 on /mnt, for example:

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

Each directory hierarchy acts as a mirror of the other. The same files are accessible in either location. However, any submounts aren't replicated. These mirrors don't provide data redundancy.

To mount a file over another file, you would use the following command:

sudo touch /mnt/foo

sudo mount -B /etc/hosts /mnt/foo

In the previous example, the /etc/hosts and /mnt/foo mount points represent the same file. The existing file that acts as a mount point isn't accessible until you unmount the overlying file.

To include submounts in the mirror, use the -R option to create a recursive bind.

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

sudo mount -o remount,ro /mnt/foo

You can mark the submounts in a mount point as being shared, private, or secondary. You can specify the following options:

mount --make-shared mount_point

Any mounts or unmounts under the specified mount point propagate to any mirrors that you create, and this mount hierarchy reflects mounts or unmount changes that you make to other mirrors.

mount --make-private mount_point

Any mounts or unmounts under the specified mount point don't propagate to other mirrors, nor does this mount hierarchy reflect mounts or unmount changes that you make to other mirrors.

mount --make-slave mount_point

Any mounts or unmounts under the specified mount point don't propagate to other mirrors, but this mount hierarchy does reflect mounts or unmount changes that you make to other mirrors.

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

sudo mount --make-unbindable mount_point

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

sudo touch /mnt/foo

sudo mount -M /mnt/foo /mnt/bar

To unmount a file system, use the umount command:

sudo umount /var/projects

Or, you can specify the block device if it's mounted on only one mount point.

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

You can identify the mount command behavior by using the -o option to specify options in a comma-separated list. Some of these options are as follows:

auto

Causes the file system to be mounted automatically by using the mount -a command.

exec

Causes the execution of any binary files in the file system.

loop

Uses a loop device (/dev/loop*) to mount a file that contains a file system image. See Mounting a File That Contains a File System Image, Creating a File System on a File Within Another File System, and the losetup(8) manual page.

Note:

The default number of available loop devices is 8. You can use the kernel boot parameter max_loop=N to configure up to 255 devices. Or, add the following entry to /etc/modprobe.conf:

options loop max_loop=N 

In the previous example, N is the number of loop devices that you require (from 0 to 255), and then reboot the system.

noauto

Prevents the file system from being mounted automatically when mount -a is issued.

noexec

Prevents the execution of any binary files in the file system.

nouser

Prevents any user other than the root user from mounting or unmounting the file system.

remount

Remounts the file system if it's already mounted. You would typically combine this option with another option such as ro or rw to change the behavior of a mounted file system.

ro

Mounts a file system as read-only.

rw

Mounts a file system for reading and writing.

user

Allows any user to mount or unmount the file system.

The following examples show different ways to use the mount -o command syntax.

• Mount the /dev/sdd1 file system as /test with read-only access and grant only the root user to mount or unmount the file system:

  sudo mount -o nouser,ro /dev/sdd1 /test

• Mount an ISO image file on /mount/cdrom with read-only access by using the loop device:

  sudo mount -o ro,loop ./Linux-Server-dvd.iso /media/cdrom

• Remount the /test file system with both read and write access, and prohibit the execution of any binary files that are in the file system:

  sudo mount -o remount,rw,noexec /test

A loop device lets you access a file as a block device. For example, you can mount a file that contains a DVD ISO image on the directory mount point /ISO as follows:

sudo mount -t iso9660 -o ro,loop /var/ISO_files/V33411-01.iso /ISO

If required, create a permanent entry for the file system in the /etc/fstab file, for example:

/var/ISO_files/V33411-01.iso          /ISO      iso9660    ro,loop     0 0

The /etc/fstab file contains the file system mount table, which provides all the information that the mount command requires to mount block devices or implement binding of mounts. If you add a file system, you must create the appropriate entry in the /etc/fstab file to ensure that the file system is mounted at boot time. The following are typical entries from this file:

/dev/sda1         /boot   ext4     defaults  1 2
/dev/sda2         /       ext4     defaults  1 1
/dev/sda3         swap    swap     defaults  0 0

The descriptions of each field in the previous output are as follows:

• The first field indicates the device to mount, which is specified by the device name, UUID, or device label, or the specification of a remote file system. A UUID or device label is preferable to a device name if the device name could change, for example:

  LABEL=Projects    /var/projects  ext4  defaults  1 2

  Note that the first field specifies the path of the file system, directory hierarchy, or file that's to be mounted on the mount point specified by the second field. The third and fourth fields are specified as none and bind.

• The second field is either the mount point for a file system or swap to indicate a swap partition. The mount point must be a path to either a file or a directory.

• The third field is the file system type, such as ext4 or swap.

• The fourth field specifies any mount options.

• The fifth column specifies whether the dump command dumps the file system (1) or not (0).

• The sixth column identifies the order by which the fsck command performs a file system check at boot time. The root file system has the value 1, while other file systems have 2. A value of 0 skips checking, as is appropriate for swap, for file systems that aren't mounted at boot time, and for binding of existing mounts.

For bind mounts, only the first four fields are specified, for example:

path    mount_point    none     bind

For more information, see the fstab(5) manual page.