Linux fstab: Automatic Disk Mounting Guide

The /etc/fstab file stores the configuration of which devices should be mounted and what the mount point of each one is during the operating system boot, even local and remote devices.

The /etc/fstab file configuration contains the following fields:

• Device: Specifies the device to be mounted. It can be the device name in /dev, UUID or LABEL;
• Mount Point: Specifies the directory where the device will be mounted;
• File System Type: Specifies the file system type to be mounted;
• Mount Options: Specifies mount options depending on the file system type;
• Backup Frequency: The dump program queries the file to determine backup frequency. It's a numeric field, where 1 is for ext2 systems and 0 for others;
• Disk Check: determines whether the device should or should not be checked during system boot by fsck. It's a numeric field, where 0 is for no checking, 1 is for checking first (root system) and 2 for checking after the root system.

Fields can be separated by a single space, or TAB.

Each line in /etc/fstab must be a separate mount point and must contain all these fields so that the /etc/fstab entry is correct.

The most common file system types are: ext2, ext3, ext4, reiserfs, xfs, btrfs, vfat, iso9660, nfs, swap, etc.

The available mount options are:

Option	Description
auto	Enables the device to be mounted during operating system boot.
noauto	Disables the device from being mounted during operating system boot.
ro	Mounts the file system as read-only.
rw	Mounts the file system for reading and writing.
exec	Enables the execution of files on the specified file system.
noexec	Disables the execution of files.
user	Allows any user to mount the device.
nouser	Only the superuser can mount and unmount the device.
sync	Enables synchronous data transfer on the device.
async	Enables asynchronous data transfer on the device.
dev	Character special device.
suid	Enables executables to have suid and sgid bits and run as if they were the superuser.
nosuid	Disables executables from having suid and sgid bits.
defaults	Configures mount options as rw, suid, exec, auto, nouser and async.

Example /etc/fstab:

$ cat /etc/fstab UUID=8a9e0fcb-f415-4a3f-931d-919fadf8e22c  /     xfs    defaults 0   1
/dev/xvdf                                  /home ext4   defaults 0   1
/dev/xvdg                                  swap  swap   defaults 0   0

In this example, the device that was mounted as root using UUID notation has the xfs file system, with default options. Another disk /dev/xvdf was mounted as the /home directory of the system, using ext4.

Also, /etc/fstab contains information about the partition used as swap. In this case the mount point will be swap, as well as the type will also be swap. This way, when the computer restarts, the swap partition will be automatically enabled with the "swapon" command.

Remember that the mount command with the -a option remounts all devices configured in /etc/fstab.

It's common to use disk UUIDs in /etc/fstab in order to avoid the disk name in /dev/ being changed due to some hardware change, such as for example the insertion of a new disk.

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