fstab

The fstab(5) file can be used to define how disk partitions, various other block devices, or remote file systems should be mounted into the file system.

Each file system is described in a separate line. These definitions will be converted into systemd mount units dynamically at boot, and when the configuration of the system manager is reloaded. The default setup will automatically fsck and mount file systems before starting services that need them to be mounted. For example, systemd automatically makes sure that remote file system mounts like NFS or Samba are only started after the network has been set up. Therefore, local and remote file system mounts specified in /etc/fstab should work out-of-the-box. See systemd.mount(5) for details.

The mount command will use fstab, if just one of either directory or device is given, to fill in the value for the other parameter. When doing so, mount options which are listed in fstab will also be used.

Usage

A simple /etc/fstab, using file system UUIDs:

describes the block special device or remote file system to be mounted; see #Identifying file systems.
describes the mount directory.
<type> the file system type.
<options> the associated mount options; see and .
is checked by the utility. This field is usually set to , which disables the check.
sets the order for file system checks at boot time; see . For the root device it should be . For other partitions it should be 2, or to disable checking.

Tip:

The auto type lets the mount command guess what type of file system is used. This is useful for optical media (CD/DVD/Blu-ray).
If the root file system is btrfs or XFS, the fsck order should be set to 0 instead of 1. See fsck.btrfs(8) and fsck.xfs(8).

All specified devices within /etc/fstab will be automatically mounted on startup and when the flag is used with unless the option is specified. Devices that are listed and not present will result in an error unless the option is used.

See for details.

Identifying file systems

There are different ways to identify file systems that will be mounted in /etc/fstab: kernel name descriptor, file system label and UUID, and GPT partition label and UUID for GPT disks. Kernel name descriptors should not be used, while UUIDs or PARTUUIDs should be preferred over labels. See Persistent block device naming for more explanations. It is recommended to read that article first before continuing with this article.

In this section, we will describe how to mount file systems using all the mount methods available via examples. The output of the commands and used in the following examples are available in the article Persistent block device naming.

To use kernel name descriptors, use in the first column.

Kernel name descriptors

Run to list the partitions and prefix the values in the NAME column with /dev/.

File system labels

Run to list the partitions, and prefix the values in the LABEL column with LABEL= or alternatively run and use the LABEL values without the quotes:

File system UUIDs

Run to list the partitions, and prefix the values in the UUID column with or alternatively run and use the UUID values without the quotes:

GPT partition labels

Run to list the partitions, and use the PARTLABEL values without the quotes:

GPT partition UUIDs

Run to list the partitions, and use the PARTUUID values without the quotes:

Tips and tricks

Automount with systemd

See systemd.mount(5) for all systemd mount options.

Local partition

In case of a large partition, it may be more efficient to allow services that do not depend on it to start while it is checked by fsck. This can be achieved by adding the following options to the /etc/fstab entry of the partition:

noauto,x-systemd.automount

This will fsck and mount the partition only when it is first accessed, and the kernel will buffer all file access to it until it is ready. This method can be relevant if one has, for example, a significantly large partition.

Note: This will make the file system type autofs which is ignored by mlocate by default.

Remote file system

The same applies to remote file system mounts. If you want them to be mounted only upon access, you will need to use the parameters. In addition, you can use the option to specify how long systemd should wait for the mount command to finish. Also, the option ensures systemd understands that the mount is network dependent and order it after the network is online.

noauto,x-systemd.automount,x-systemd.mount-timeout=30,_netdev

Encrypted file system

If you have encrypted file systems with keyfiles, you can also add the parameter to the corresponding entries in . systemd will then not open the encrypted device on boot, but instead wait until it is actually accessed and then automatically open it with the specified keyfile before mounting it. This might save a few seconds on boot if you are using an encrypted RAID device for example, because systemd does not have to wait for the device to become available. For example:

Automatic unmount

You may also specify an idle timeout for a mount with the flag. For example:

noauto,x-systemd.automount,x-systemd.idle-timeout=1min

This will make systemd unmount the mount after it has been idle for 1 minute.

External devices

External devices that are to be mounted when present but ignored if absent may require the option. This prevents errors being reported at boot. For example:

/etc/fstab

/dev/sdg1        /media/backup    jfs    nofail,x-systemd.device-timeout=1ms    0  2

The option is best combined with the option. This is because the default device timeout is 90 seconds, so a disconnected external device with only will make your boot take 90 seconds longer, unless you reconfigure the timeout as shown. Make sure not to set the timeout to 0, as this translates to infinite timeout.

Filepath spaces

Since spaces are used in to delimit fields, if any field (PARTLABEL, LABEL or the mount point) contains spaces, these spaces must be replaced by escape characters followed by the 3 digit octal code 040:

atime options

Below atime options can impact drive performance.

The option updates the access time of the files every time they are accessed. This is more purposeful when Linux is used for servers; it does not have much value for desktop use. The drawback about the option is that even reading a file from the page cache (reading from memory instead of the drive) will still result in a write.
The option fully disables writing file access times to the drive every time you read a file. This works well for almost all applications, except for those that need to know if a file has been read since the last time it was modified. The write time information to a file will continue to be updated anytime the file is written to with this option enabled.
The option disables the writing of file access times only for directories while other files still get access times written.
Note: noatime implies nodiratime. You do not need to specify both.
updates the access time only if the previous access time was earlier than the current modify or change time. In addition, since Linux 2.6.30, the access time is always updated if the previous access time was more than 24 hours old. This option is used when the option, option (which means to use the kernel default, which is ; see and wikipedia:Stat (system call)#Criticism of atime) or no options at all are specified.

When using Mutt or other applications that need to know if a file has been read since the last time it was modified, the option should not be used; using the option is acceptable and still provides a performance improvement.

Since kernel 4.0 there is another related option:

reduces writes to disk by maintaining changes to inode timestamps (access, modification and creation times) only in memory. The on-disk timestamps are updated only when either (1) the file inode needs to be updated for some change unrelated to file timestamps, (2) a sync to disk occurs, (3) an undeleted inode is evicted from memory or (4) if more than 24 hours passed since the the last time the in-memory copy was written to disk.

Warning: In the event of a system crash, the access and modification times on disk might be out of date by up to 24 hours.

Note that the option works in combination with the aforementioned options, not as an alternative. That is by default, but can be even with the same or less cost of disk writes as the plain option.

Remounting the root partition

If for some reason the root partition has been improperly mounted read only, remount the root partition with read-write access with the following command:

# mount -o remount,rw /

GPT partition automounting

When using UEFI/GPT, it is possible to omit certain partitions from /etc/fstab by partitioning according to the Discoverable Partitions Specification and have mount the partitions. See systemd#GPT partition automounting.

Bind mount

You can link directories with the option: