Red Hat Training

A Red Hat training course is available for RHEL 8

Chapter 14. Mounting file systems

As a system administrator, you can mount file systems on your system to access data on them.

14.1. The Linux mount mechanism

This section explains basic concepts of mounting file systems on Linux.

On Linux, UNIX, and similar operating systems, file systems on different partitions and removable devices (CDs, DVDs, or USB flash drives for example) can be attached to a certain point (the mount point) in the directory tree, and then detached again. While a file system is mounted on a directory, the original content of the directory is not accessible.

Note that Linux does not prevent you from mounting a file system to a directory with a file system already attached to it.

When mounting, you can identify the device by:

  • a universally unique identifier (UUID): for example, UUID=34795a28-ca6d-4fd8-a347-73671d0c19cb
  • a volume label: for example, LABEL=home
  • a full path to a non-persistent block device: for example, /dev/sda3

When you mount a file system using the mount command without all required information, that is without the device name, the target directory, or the file system type, the mount utility reads the content of the /etc/fstab file to check if the given file system is listed there. The /etc/fstab file contains a list of device names and the directories in which the selected file systems are set to be mounted as well as the file system type and mount options. Therefore, when mounting a file system that is specified in /etc/fstab, the following command syntax is sufficient:

  • Mounting by the mount point:

    # mount directory
  • Mounting by the block device:

    # mount device

Additional resources

14.2. Listing currently mounted file systems

This procedure describes how to list all currently mounted file systems on the command line.

Procedure

  • To list all mounted file systems, use the findmnt utility:

    $ findmnt
  • To limit the listed file systems only to a certain file system type, add the --types option:

    $ findmnt --types fs-type

    For example:

    Example 14.1. Listing only XFS file systems

    $ findmnt --types xfs
    
    TARGET  SOURCE                                                FSTYPE OPTIONS
    /       /dev/mapper/luks-5564ed00-6aac-4406-bfb4-c59bf5de48b5 xfs    rw,relatime
    ├─/boot /dev/sda1                                             xfs    rw,relatime
    └─/home /dev/mapper/luks-9d185660-7537-414d-b727-d92ea036051e xfs    rw,relatime

Additional resources

  • findmnt(8) man page

14.3. Mounting a file system with mount

This procedure describes how to mount a file system using the mount utility.

Prerequisites

  • Make sure that no file system is already mounted on your chosen mount point:

    $ findmnt mount-point

Procedure

  1. To attach a certain file system, use the mount utility:

    # mount device mount-point

    Example 14.2. Mounting an XFS file system

    For example, to mount a local XFS file system identified by UUID:

    # mount UUID=ea74bbec-536d-490c-b8d9-5b40bbd7545b /mnt/data
  2. If mount cannot recognize the file system type automatically, specify it using the --types option:

    # mount --types type device mount-point

    Example 14.3. Mounting an NFS file system

    For example, to mount a remote NFS file system:

    # mount --types nfs4 host:/remote-export /mnt/nfs

Additional resources

  • mount(8) man page

14.4. Moving a mount point

This procedure describes how to change the mount point of a mounted file system to a different directory.

Procedure

  1. To change the directory in which a file system is mounted:

    # mount --move old-directory new-directory

    Example 14.4. Moving a home file system

    For example, to move the file system mounted in the /mnt/userdirs/ directory to the /home/ mount point:

    # mount --move /mnt/userdirs /home
  2. Verify that the file system has been moved as expected:

    $ findmnt
    $ ls old-directory
    $ ls new-directory

Additional resources

  • mount(8) man page

14.5. Unmounting a file system with umount

This procedure describes how to unmount a file system using the umount utility.

Procedure

  1. Try unmounting the file system using either of the following commands:

    • By mount point:

      # umount mount-point
    • By device:

      # umount device

    If the command fails with an error similar to the following, it means that the file system is in use because of a process is using resources on it:

    umount: /run/media/user/FlashDrive: target is busy.
  2. If the file system is in use, use the fuser utility to determine which processes are accessing it. For example:

    $ fuser --mount /run/media/user/FlashDrive
    
    /run/media/user/FlashDrive: 18351

    Afterwards, terminate the processes using the file system and try unmounting it again.

14.6. Common mount options

This section lists some commonly used options of the mount utility.

You can use these options in the following syntax:

# mount --options option1,option2,option3 device mount-point

Table 14.1. Common mount options

OptionDescription

async

Enables asynchronous input and output operations on the file system.

auto

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

defaults

Provides an alias for the async,auto,dev,exec,nouser,rw,suid options.

exec

Allows the execution of binary files on the particular file system.

loop

Mounts an image as a loop device.

noauto

Default behavior disables the automatic mount of the file system using the mount -a command.

noexec

Disallows the execution of binary files on the particular file system.

nouser

Disallows an ordinary user (that is, other than root) to mount and unmount the file system.

remount

Remounts the file system in case it is already mounted.

ro

Mounts the file system for reading only.

rw

Mounts the file system for both reading and writing.

user

Allows an ordinary user (that is, other than root) to mount and unmount the file system.