Difference between revisions of "Fstab"
m (→Automount with systemd: use full sentence)
m (→Automount with systemd: use full sentence)
Latest revision as of 16:51, 9 February 2018
Thefile 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 or Samba 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 for details.
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.
- 1 Usage
- 2 Identifying filesystems
- 3 Tips and tricks
- 4 See also
/etc/fstab, using kernel name descriptors:
# <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 .
<dump>is checked by the utility. This field is usually set to
0, which disables the check.
<fsck>sets the order for filesystem checks at boot time; see . For the root device it should be
1. For other partitions it should be
0to disable checking.
autotype lets the mount command guess what type of file system is used. This is useful for optical media (CD/DVD).
All specified devices within
/etc/fstab will be automatically mounted on startup and when the
-a flag is used with unless the
noauto option is specified. Devices that are listed and not present will result in an error unless the
nofail option is used.
There are different ways to identify filesystems that will be mounted in
/etc/fstab: 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.
To use kernel name descriptors, use /dev/sdxy in the first column.
Kernel name descriptors
lsblk -f to list the partitions and prefix the values in the NAME column with
# <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,data=ordered 0 1 /dev/sda3 /home ext4 rw,relatime,data=ordered 0 2 /dev/sda4 none swap defaults 0 0
lsblk -f to list the partitions, and prefix the values in the LABEL column with
# <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,data=ordered 0 1 LABEL=DATA /home ext4 rw,relatime,data=ordered 0 2 LABEL=SWAP none swap defaults 0 0
lsblk -f to list the partitions, and prefix the values in the UUID column with
# <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,data=ordered 0 1 UUID=b411dc99-f0a0-4c87-9e05-184977be8539 /home ext4 rw,relatime,data=ordered 0 2 UUID=f9fe0b69-a280-415d-a03a-a32752370dee none swap defaults 0 0
lsblk -no UUID /dev/sda2.
blkid to list the partitions, and use the PARTLABEL values without the quotes:
# <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,data=ordered 0 1 PARTLABEL=HOME /home ext4 rw,relatime,data=ordered 0 2 PARTLABEL=SWAP none swap defaults 0 0
blkid to list the partitions, and use the PARTUUID values without the quotes:
# <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,data=ordered 0 1 PARTUUID=7280201c-fc5d-40f2-a9b2-466611d3d49e /home ext4 rw,relatime,data=ordered 0 2 PARTUUID=039b6c1c-7553-4455-9537-1befbc9fbc5b none swap defaults 0 0
Tips and tricks
Automount with systemd
Seefor all systemd mount options.
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:
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
autofswhich is ignored by mlocate by default.
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 how long systemd should wait for the filesystem to show up. Also, the
_netdev option ensures systemd understands that the mount is network dependent and order it after the network is online.
execflag with automount, you should remove the
userflag for it to work properly as found in the course of a Fedora Bug Report
If you have encrypted filesystems with keyfiles, you can also add the
noauto parameter to the corresponding entries in
/etc/crypttab. 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:
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:
This will make systemd unmount the mount after it has been idle for 1 minute.
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:
/dev/sdg1 /media/backup jfs defaults,nofail,x-systemd.device-timeout=1 0 2
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:
//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
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
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
Below atime options can impact drive performance.
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 the
strictatimeoption is that even reading a file from the page cache (reading from memory instead of the drive) will still result in a write!
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.
nodiratimeoption disables the writing of file access times only for directories while other files still get access times written.
nodiratime. You do not need to specify both.
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 the
atimeoption (which means to use the kernel default, which is
relatime; 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
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.
- 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
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
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 /