fstab
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The fstab(5) file can be used to define how disk partitions, various other block devices, or remote filesystems should be mounted into the filesystem.
Each filesystem 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 filesystems before starting services that need them to be mounted. For example, systemd automatically makes sure that remote filesystem mounts like NFS orSamba are only started after the network has been set up. Therefore, local and remote filesystem 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 kernel name descriptors:/etc/fstab
# <device> <dir> <type> <options> <dump> <fsck> /dev/sda1 / ext4 defaults,noatime 0 1 /dev/sda2 none swap defaults 0 0 /dev/sda3 /home ext4 defaults,noatime 0 2
<device>describes the block special device or remote filesystem to be mounted; see #Identifying_filesystems.<dir>describes the mount directory,<type>the file system type, and<options>the associated mount options; see mount(8).<dump>is checked by the dump(8) utility.<fsck>sets the order for filesystem checks at boot time; see fsck(8).
See fstab(5) for details.
Identifying filesystems
There are different ways to identify filesystems that will be mounted.
/etc/fstab does support several methods: kernel name descriptor, label or UUID, and GPT labels and UUID for GPT disks. UUID must be privileged over kernel name descriptors and 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 filesystems using all the mount methods available via examples. The output of the commands
lsblk -f and blkid used in the following examples are available in the article Persistent block device naming. If you have not read that article yet, please read it now.Kernel name descriptors
Run
lsblk -f to list the partitions and prefix the values in the NAME column with /dev/./etc/fstab
# <device> <dir> <type> <options> <dump> <fsck> /dev/sda1 /boot vfat rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro 0 2 /dev/sda2 / ext4 rw,relatime,discard,data=ordered 0 1 /dev/sda3 /home ext4 rw,relatime,discard,data=ordered 0 2 /dev/sda4 none swap defaults 0 0
Labels
Run
lsblk -f to list the partitions, and prefix the values in the LABEL column with LABEL=:/etc/fstab
# <device> <dir> <type> <options> <dump> <fsck> LABEL=EFI /boot vfat rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro 0 2 LABEL=SYSTEM / ext4 rw,relatime,discard,data=ordered 0 1 LABEL=DATA /home ext4 rw,relatime,discard,data=ordered 0 2 LABEL=SWAP none swap defaults 0 0
UUIDs
Run
lsblk -f to list the partitions, and prefix the values in the UUID column with UUID=:/etc/fstab
# <device> <dir> <type> <options> <dump> <fsck> UUID=CBB6-24F2 /boot vfat rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro 0 2 UUID=0a3407de-014b-458b-b5c1-848e92a327a3 / ext4 rw,relatime,discard,data=ordered 0 1 UUID=b411dc99-f0a0-4c87-9e05-184977be8539 /home ext4 rw,relatime,discard,data=ordered 0 2 UUID=f9fe0b69-a280-415d-a03a-a32752370dee none swap defaults 0 0
GPT labels
Run
blkid to list the partitions, and use the PARTLABEL values without the quotes:/etc/fstab
# <device> <dir> <type> <options> <dump> <fsck> PARTLABEL=EFI\040SYSTEM\040PARTITION /boot vfat rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro 0 2 PARTLABEL=GNU/LINUX / ext4 rw,relatime,discard,data=ordered 0 1 PARTLABEL=HOME /home ext4 rw,relatime,discard,data=ordered 0 2 PARTLABEL=SWAP none swap defaults 0 0
GPT UUIDs
Run
blkid to list the partitions, and use the PARTUUID values without the quotes:/etc/fstab
# <device> <dir> <type> <options> <dump> <fsck> PARTUUID=d0d0d110-0a71-4ed6-936a-304969ea36af /boot vfat rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro 0 2 PARTUUID=98a81274-10f7-40db-872a-03df048df366 / ext4 rw,relatime,discard,data=ordered 0 1 PARTUUID=7280201c-fc5d-40f2-a9b2-466611d3d49e /home ext4 rw,relatime,discard,data=ordered 0 2 PARTUUID=039b6c1c-7553-4455-9537-1befbc9fbc5b none swap defaults 0 0
Tips and tricks
Automount with systemd
If you have a large
/home partition, it might be better to allow services that do not depend on /home to start while /home is checked by fsck. This can be achieved by adding the following options to the /etc/fstab entry of your /home partition:noauto,x-systemd.automount
This will fsck and mount
/home when it is first accessed, and the kernel will buffer all file access to /home until it is ready.
The same applies to remote filesystem mounts. If you want them to be mounted only upon access, you will need to use the
noauto,x-systemd.automount parameters. In addition, you can use the x-systemd.device-timeout=# option to specify a timeout in case the network resource is not available.
If you have encrypted filesystems with keyfiles, you can also add the
noauto parameter to the corresponding entries in /etc/crypttab. systemdwill 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:/etc/crypttab
data /dev/md0 /root/key noauto
You may also specify an idle timeout for a mount with the
x-systemd.idle-timeout 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
nofail option. This prevents errors being reported at boot. For example:/etc/fstab
/dev/sdg1 /media/backup jfs defaults,nofail,x-systemd.device-timeout=1 0 2
The
nofail option is best combined with the x-systemd.device-timeout option. This is because the default device timeout is 90 seconds, so a disconnected external device with only nofail 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.
If your external device requires another systemd unit to be loaded (for example the network for a network share) you can use
x-systemd.requires=x combined with x-systemd.automountto postpone automounting until after the unit is available. For example:/etc/fstab
//host/share /net/share cifs noauto,nofail,x-systemd.automount,x-systemd.requires=network-online.target,x-systemd.device-timeout=10,workgroup=workgroup,credentials=/foo/credentials 0 0
Filepath spaces
Since spaces are used in
fstab 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:/etc/fstab
UUID=47FA-4071 /home/username/Camera\040Pictures vfat defaults,noatime 0 0 /dev/sda7 /media/100\040GB\040(Storage) ext4 defaults,noatime,user 0 2
atime options
Below atime options can impact drive performance.
- The
strictatimeoption 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 thestrictatimeoption is that even reading a file from the page cache (reading from memory instead of the drive) will still result in a write!
- The
noatimeoption 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
nodiratimeoption disables the writing of file access times only for directories while other files still get access times written.
relatimeupdates 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 thedefaultsoption,atimeoption (which means to use the kernel default, which isrelatime; see mount(8) 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
noatime option should not be used; using the relatime option is acceptable and still provides a performance improvement.
Since kernel 4.0 there is another related option:
lazytimereduces 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.
Note that the
lazytime option works in combination with the aforementioned *atime options, not as an alternative. That is relatime by default, but can be even strictatime with the same or less cost of disk writes as the plain relatime option.Writing to FAT32 as Normal User
To write on a FAT32 partition, you must make a few changes to your
/etc/fstab file./etc/fstab
/dev/sdxY /mnt/some_folder vfat user,rw,umask=000 0 0
The
user flag means that any user (even non-root) can mount and unmount the partition /dev/sdX. rw gives read-write access; umask option removes selected rights - for example umask=111 remove executable rights. The problem is that this entry removes executable rights from directories too, so we must correct it by dmask=000. See also Umask.
Without these options, all files will be executable. You can use the option
showexec instead of the umask and dmask options, which shows all Windows executables (com, exe, bat) in executable colours.
For example, if your FAT32 partition is on
/dev/sda9, and you wish to mount it to /mnt/fat32, then you would use:/etc/fstab
/dev/sda9 /mnt/fat32 vfat user,rw,umask=111,dmask=000 0 0
Now, any user can mount it with:
$ mount /mnt/fat32
And unmount it with:
$ umount /mnt/fat32
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 /
bind mounts
Sometimes programs or users cannot access one specific directory due to insufficient permissions. One feasable possibility to give the program access to this directory is bind mounting it to a location the program can access. If a program has permission to access directory bar but not to directory foo, under some circumstances the access can be granted without any permission hassle by adding an entry to
/etc/fstab:/etc/fstab
/<path to foo> /<path to bar> none bind 0 0
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