Difference between revisions of "Fstab"

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[[Category:File systems (English)]]
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{{Lowercase title}}
[[Category:Boot process (English)]]
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[[Category:File systems]]
{{i18n|Fstab}}
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[[Category:Boot process]]
{{Lowercase_title}}
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[[ar:Fstab]]
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[[es:Fstab]]
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[[fr:Fstab]]
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[[hu:Fstab]]
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[[it:Fstab]]
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[[ja:Fstab]]
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[[ro:Fstab]]
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[[ru:Fstab]]
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[[zh-hans:Fstab]]
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[[zh-hant:Fstab]]
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{{Related articles start}}
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{{Related|Persistent block device naming}}
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{{Related|File systems}}
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{{Related|tmpfs}}
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{{Related|swap}}
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{{Related articles end}}
  
The {{Filename|/etc/fstab}} file contains static filesystem information.  It defines how storage devices and partitions are to be initialized and integrated into the overall system.
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The {{man|5|fstab}} file can be used to define how disk partitions, various other block devices, or remote filesystems should be mounted into the filesystem.
  
== Example ==
+
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 {{ic|/etc/fstab}} should work out of the box. See {{man|5|systemd.mount}} for details.
  
Here is an example {{Filename|/etc/fstab}} using kernel naming (/dev/sdx) descriptors:
+
The {{ic|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.
<pre>
 
# <file system>        <dir>        <type>    <options>            <dump> <pass>
 
devpts                /dev/pts      devpts    defaults              0      0
 
shm                    /dev/shm      tmpfs    nodev,nosuid          0      0
 
 
/dev/sda2              /            ext4      defaults,noatime      0      1
 
/dev/sda6              /home        ext4      defaults,noatime      0      2
 
/dev/sda7              swap          swap      defaults              0      0
 
</pre>
 
  
Here is another example using more mount options and the LABEL= method of identifying mountable devices.
+
== Usage ==
<pre>
 
devpts                /dev/pts      devpts    defaults              0      0
 
shm                    /dev/shm      tmpfs    nodev,nosuid          0      0
 
  
LABEL=BOOT      /boot          ext2 defaults              0 2
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A simple {{ic|/etc/fstab}}, using kernel name descriptors:
LABEL=ROOT      /               ext4 defaults,noatime      0 1
 
LABEL=USR      /usr            ext4 defaults,noatime      0 2
 
LABEL=VAR      /var            ext4 defaults,noatime      0 2
 
LABEL=OPT      /opt            ext4 defaults,noatime      0 2
 
LABEL=HOME      /home          ext4 defaults,noatime      0 2
 
</pre>
 
  
==Field definitions==
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{{hc|/etc/fstab|
{{Filename|/etc/fstab}} contains the following fields separated by a space or tab:
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# <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}}
  
<file system> <dir> <type> <options> <dump> <pass>
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* {{ic|<device>}} describes the block special device or remote filesystem to be mounted; see [[#Identifying filesystems]].
 +
* {{ic|<dir>}} describes the [[mount]] directory, {{ic|<type>}} the [[file system]] type, and {{ic|<options>}} the associated mount options; see {{man|8|mount|FILESYSTEM-INDEPENDENT_MOUNT_OPTIONS}}.
 +
* {{ic|<dump>}} is checked by the {{man|8|dump|url=http://linux.die.net/man/8/dump}} utility.
 +
* {{ic|<fsck>}} sets the order for filesystem checks at boot time; see {{man|8|fsck}}.
  
* '''<file systems>''' - defines the storage device (i.e. {{Filename|/dev/sda1}}).
+
{{Tip|The {{ic|auto}} type lets the mount command guess what type of file system is used. This is useful for optical media (CD/DVD).}}
* '''<dir>''' - tells the mount command where it should mount the <file system> to.
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{{Note|If the root file system is [[btrfs]], the fsck order should be set to {{ic|0}} instead of {{ic|1}}.}}
* '''<type>''' - defines the file system type of the device or partition to be mounted. Many different file systems are supported. Some examples are: ext2, ext3, reiserfs, xfs, jfs, smbfs, iso9660, vfat, ntfs, swap, and auto. The 'auto' type lets the mount command to attempt to guess what type of file system is used, this is useful for removable devices such as cdroms and dvds.  
 
* '''<options>''' - define particular options for filesystems.  Some options relate only to the filesystem itself. Some of the more common options are:
 
  
:* auto - File system will mount automatically at boot, or when the command 'mount -a' is issued.
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All specified devices within {{ic|/etc/fstab}} will be automatically mounted on startup and when the {{ic|-a}} flag is used with {{man|8|mount}} unless the {{ic|noauto}} option is specified. Devices that are listed and not present will result in an error unless the {{ic|nofail}} option is used.
:* noauto - The filesystem is mounted only when you tell it to.
 
:* exec - Allow the execution binaries that are on that partition (default).
 
:* noexec - Do not allow binaries to be executed on the filesystem.
 
:* ro - Mount the filesystem read only
 
:* rw - Mount the filesystem read-write
 
:* sync - I/O should be done synchronously
 
:* async - I/O should be done asynchronously
 
:* flush - specific option for FAT to flush data more often, thus making copy dialogs or progress bars to stays up until things are on the disk
 
:* user - Permit any user to mount the filesystem (implies noexec,nosuid,nodev unless overridden.)
 
:* nouser - Only allow root to mount the filesystem. (default)
 
:* defaults - Default mount settings (equivalent to rw,suid,dev,exec,auto,nouser,async).
 
:* suid - Allow the operation of suid, and sgid bits. They are mostly used to allow users on a computer system to execute binary executables with temporarily elevated privileges in order to perform a specific task.
 
:* nosuid - Block the operation of suid, and sgid bits.
 
:* noatime - Do not update inode access times on the filesystem. Can help performance (see [[#atime_options|atime options]]).
 
:* nodiratime - Do not update directory inode access times on the filesystem. Can help performance (see [[#atime_options|atime options]]).
 
:* relatime - Update inode access times relative to modify or change time. Access time is only updated if the previous access time was earlier than the current modify or change time. (Similar to noatime, but doesn't break mutt or other applications that need to know if a file has been read since the last time it was modified.) Can help performance (see [[#atime_options|atime options]]).
 
* '''<dump>''' - Is used by the dump utility to decide when to make a backup. When installed (not installed by a standard installation of Arch Linux), dump checks the entry and uses the number to decide if a file system should be backed up. Possible entries are 0 and 1. If 0, dump will ignore the file system, if 1, dump will make a backup. Most users will not have dump installed, so they should put 0 for the <dump> entry.
 
* '''<pass>''' fsck reads the <pass> number and determines in which order the file systems should be checked.  Possible entries are 0, 1, and 2. The root file system should have the highest priority, 1, all other file systems you want to have checked should get a 2.  File systems with a <pass> value 0 will not be checked by the fsck utility.
 
  
== Defining filesystems ==
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See {{man|5|fstab|DESCRIPTION}} for details.
  
You can define the filesystems in the {{Filename|/etc/fstab}} configuration in three different ways: by kernel naming descriptors, by UUID, or by labels.  The advantage of using UUIDs or labels is that they are not dependent on disk order.  This is useful if you change your storage device order in the BIOS, you switch storage device cabling, or because some BIOS's may occasionally change the order of storage devices.
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== Identifying filesystems ==
  
=== Kernel naming ===
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There are different ways to identify filesystems that will be mounted in {{ic|/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.
  
You can get kernel naming descriptors using {{Codeline|fdisk}}:
+
In this section, we will describe how to mount filesystems using all the mount methods available via examples. The output of the commands {{ic|lsblk -f}} and {{ic|blkid}} used in the following examples are available in the article [[Persistent block device naming]].
  
<pre>
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To use kernel name descriptors, use /dev/sd''xy'' in the first column.
# fdisk -l
+
 
...
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=== Kernel name descriptors ===
 
+
 
Device Boot     Start        End      Blocks  Id  System
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Run {{ic|lsblk -f}} to list the partitions and prefix the values in the ''NAME'' column with {{ic|/dev/}}.
/dev/sda1  *          1       2550    20482843+  b  W95 FAT32
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/dev/sda2           2551        5100    20482875   83  Linux
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{{hc|/etc/fstab|<nowiki>
/dev/sda3           5101        7650    20482875   83  Linux
+
# <device>     <dir> <type> <options>                                                                                            <dump> <fsck>
/dev/sda4           7651     121601  915311407+  5  Extended
+
/dev/sda1       /boot vfat   rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro 0      2
/dev/sda5            7651      10200    20482843+  83  Linux
+
/dev/sda2       /    ext4   rw,relatime,discard,data=ordered                                                                    0      1
/dev/sda6          10201       17849    61440561   83  Linux
+
/dev/sda3       /home ext4   rw,relatime,discard,data=ordered                                                                    0      2
/dev/sda7          17850      18104     2048256   82  Linux swap / Solaris
+
/dev/sda4       none  swap  defaults                                                                                            0     0
/dev/sda8          18105      18113      72261   83  Linux
+
</nowiki>}}
/dev/sda9          18114     121601   831267328+  7  HPFS/NTFS
+
 
</pre>
+
=== Labels ===
 +
 
 +
Run {{ic|lsblk -f}} to list the partitions, and prefix the values in the ''LABEL'' column with {{ic|1=LABEL=}}:
 +
 
 +
{{hc|/etc/fstab|<nowiki>
 +
# <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
 +
</nowiki>}}
 +
 
 +
{{Note|If any of your fields contains spaces, see [[#Filepath spaces]].}}
  
 
=== UUIDs ===
 
=== UUIDs ===
  
UUIDs are generated by the make-filesystem utilities ({{Codeline|mkfs.*}}) when you create a filesystem.  {{Codeline|blkid}} will show you the UUIDs of mounted devices and partitions:
+
Run {{ic|lsblk -f}} to list the partitions, and prefix the values in the ''UUID'' column with {{ic|1=UUID=}}:
 +
 
 +
{{hc|/etc/fstab|<nowiki>
 +
# <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
 +
</nowiki>}}
 +
 
 +
{{Tip|If you would like to return just the UUID of a specific partition:
 +
$ lsblk -no UUID /dev/sda2}}
  
<pre>
+
=== GPT labels ===
# blkid
+
Run {{ic|blkid}} to list the partitions, and use the ''PARTLABEL'' values without the quotes:
/dev/sda1: UUID="76E4F702E4F6C401" LABEL="vista" TYPE="ntfs"
 
/dev/sda2: LABEL="Root" UUID="24f28fc6-717e-4bcd-a5f7-32b959024e26" TYPE="ext4"
 
/dev/sda6: LABEL="Home" UUID="03ec5dd3-45c0-4f95-a363-61ff321a09ff" TYPE="ext4"
 
/dev/sda7: LABEL="swap" UUID="4209c845-f495-4c43-8a03-5363dd433153" TYPE="swap"
 
/dev/sda10: UUID="0ea7a93f-537c-4868-9201-0dc090c050e4" TYPE="crypto_LUKS"
 
/dev/mapper/sda10: UUID="d3560bbb-b5d5-46c5-a7a8-434c885217c7" UUID_SUB="425ab275-d520-4636-8d16-55fb2b957971" TYPE="btrfs"
 
</pre>
 
  
An example {{Filename|/etc/fstab}} using the UUID identifiers:
+
{{hc|/etc/fstab|<nowiki>
 +
# <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
 +
</nowiki>}}
  
<pre>
+
{{Note|If any of your fields contains spaces, see [[#Filepath spaces]].}}
# <file system>        <dir>        <type>    <options>            <dump> <pass>
 
none                  /dev/pts      devpts    defaults                0      0
 
none                  /dev/shm      tmpfs    defaults                0      0
 
 
UUID=24f28fc6-717e-4bcd-a5f7-32b959024e26 /    ext4 defaults,noatime  0      1
 
UUID=03ec5dd3-45c0-4f95-a363-61ff321a09ff /home ext4 defaults,noatime  0      2
 
UUID=4209c845-f495-4c43-8a03-5363dd433153 swap  swap defaults          0      0
 
</pre>
 
  
In case your swap partition doesn't have an UUID, you can add it manually. This happens when the UUID of the swap is not shown with the {{Codeline|blkid}} command.
+
=== GPT UUIDs ===
  
First, if we don't know wich is the swap partition, we had to find it with the command:
+
Run {{ic|blkid}} to list the partitions, and use the ''PARTUUID'' values without the quotes:
  
{{Cli|$ swapon -s
+
{{hc|/etc/fstab|<nowiki>
Filename Type Size Used Priority
+
# <device>                                    <dir> <type> <options>                                                                                            <dump> <fsck>
/dev/sda7                              partition 4000148 0 -1}}
+
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
 +
</nowiki>}}
  
 +
== Tips and tricks ==
  
Then disable the swap:
+
=== Automount with systemd ===
  
<pre>
+
If you have a large {{ic|/home}} partition, it might be better to allow services that do not depend on {{ic|/home}} to start while {{ic|/home}} is checked by ''fsck''. This can be achieved by adding the following options to the {{ic|/etc/fstab}} entry of your {{ic|/home}} partition:
# swapoff /dev/sda7
 
</pre>
 
  
Now, recreate the swap with a new UUID assigned to it:
+
noauto,x-systemd.automount
  
<pre>
+
This will fsck and mount {{ic|/home}} when it is first accessed, and the kernel will buffer all file access to {{ic|/home}} until it is ready.
# mkswap -U random /dev/sda7
 
</pre>
 
  
Finally, activate the swap:
+
{{Note|This will make your {{ic|/home}} filesystem type {{ic|autofs}}, which is ignored by [[mlocate]] by default. The speedup of automounting {{ic|/home}} may not be more than a second or two, depending on your system, so this trick may not be worth it.}}
  
<pre>
+
The same applies to remote filesystem mounts. If you want them to be mounted only upon access, you will need to use the {{ic|noauto,x-systemd.automount}} parameters. In addition, you can use the {{ic|1=x-systemd.device-timeout=#}} option to specify a timeout in case the network resource is not available.
# swapon /dev/sda7
 
</pre>
 
  
=== Labels ===
+
{{Note|1=If you intend to use the {{ic|exec}} flag with automount, you should remove the {{ic|user}} flag for it to work properly as found in the course of a [https://bugzilla.redhat.com/show_bug.cgi?id=769636 Fedora Bug Report]}}
 +
 
 +
If you have encrypted filesystems with keyfiles, you can also add the {{ic|noauto}} parameter to the corresponding entries in {{ic|/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:
  
The device or partition is required to be labeled first.  To do this, you can use common applications like {{Package Official|gparted}} to label partitions or you can use {{Codeline|e2label}} to label ext2, ext3, and ext4 partitions.  Keep in mind that not all file system have labeling support (e.g. FAT file systems).
+
{{hc|/etc/crypttab|
 +
data /dev/md0 /root/key noauto}}
  
A device or partition must not be mounted before attempting to label them.  Initially you will need to boot from a Live(CD/DVD/USB) before you can label with a {{Package Official|gparted}}-like application or for ext partitions you can use {{Codeline|e2label}}.
+
You may also specify an idle timeout for a mount with the {{ic|x-systemd.idle-timeout}} flag. For example:
  
  e2label /dev/<disk-or-partition> Arch_Linux
+
  noauto,x-systemd.automount,x-systemd.idle-timeout=1min
  
Labels can be up to 16 characters long.  Technically labeling can have spaces too, however there is no way to have your {{Filename|fstab}} or [[GRUB]] configuration file (for that matter) be able to recognize them by that label if you do.
+
This will make systemd unmount the mount after it has been idle for 1 minute.
  
Labels should be unambiguous, meaning that each label should be original to prevent any possible conflicts.  To enter labels into your {{Filename|fstab}}, here is an example:
+
=== External devices ===
  
<pre>
+
External devices that are to be mounted when present but ignored if absent may require the {{ic|nofail}} option. This prevents errors being reported at boot. For example:
# <file system>        <dir>        <type>    <options>            <dump> <pass>
 
devpts                /dev/pts      devpts    defaults              0      0
 
shm                    /dev/shm      tmpfs    nodev,nosuid          0      0
 
 
LABEL=Arch_Linux      /            ext4      defaults,noatime        0      1
 
LABEL=Arch_Swap        swap          swap      defaults                0      0
 
</pre>
 
  
== Tips ==
+
{{hc|/etc/fstab|2=
 +
/dev/sdg1        /media/backup    jfs    defaults,nofail,x-systemd.device-timeout=1    0  2}}
  
=== atime options ===
+
The {{ic|nofail}} option is best combined with the {{ic|x-systemd.device-timeout}} option. This is because the default device timeout is 90 seconds, so a disconnected external device with only {{ic|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.
  
The use of {{Codeline|noatime}}, {{Codeline|nodiratime}} or {{Codeline|relatime}} can help disk performance for ext2, ext3, and ext4 filesystems.  Linux by default keeps a record (writes to the disk) every times it reads from the disk {{Codeline|atime}}.  This was more purposeful when Linux was being used for servers; it doesn't have much value for desktop use. The worst thing about the default {{Codeline|atime}} option is that even reading a file from the page cache (reading from memory instead of the disk) will still result in a disk write! Using the {{Codeline|noatime}} option fully disables writing file access times to the disk every time you read a file.  This works well for almost all applications, except for a rare few like [[Mutt]] that need the such information.  For mutt, you should only use the {{Codeline|relatime}} option. Using the {{Codeline|relatime}} option enables the writing of file access times only when the file is being modified (unlike {{Codeline|noatime}} where the file access time will never be changed and will be older than the modification time). The {{Codeline|nodiratime}} option disables the writing of file access times only for directories while other files still get access times written. The best compromise might be the use of {{Codeline|relatime}} in which case programs like [[Mutt]] will continue to work, but you'll still have a performance boost because files will not get access times updated unless they are modified.
+
If your external device requires another systemd unit to be loaded (for example the network for a network share) you can use {{ic|1=x-systemd.requires=x}} combined with {{ic|x-systemd.automount}}to postpone automounting until after the unit is available. For example:
  
{{Note|{{Codeline|noatime}} already includes {{Codeline|nodiratime}}. You don't need to specify both options.}}
+
{{hc|/etc/fstab|2=
 +
//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}}
  
===tmpfs===
+
=== Filepath spaces ===
[[Wikipedia:Tmpfs|tmpfs]] is a temporary filesystem that resides in memory and/or your swap partition(s), depending on how much you fill it up. Mounting directories as tmpfs can be an effective way of speeding up accesses to their files, or to ensure that their contents are automatically cleared upon reboot.
 
  
Some directories where tmpfs is commonly used are [http://www.pathname.com/fhs/2.2/fhs-3.15.html /tmp], [http://www.pathname.com/fhs/2.2/fhs-5.9.html /var/lock] and [http://www.pathname.com/fhs/2.2/fhs-5.13.html /var/run]. Do NOT use it on [http://www.pathname.com/fhs/2.2/fhs-5.15.html /var/tmp], because that folder is meant for temporary files that are preserved across reboots.
+
Since spaces are used in {{ic|fstab}} to delimit fields, if any field (''PARTLABEL'', ''LABEL'' or the mount point) contains spaces, these spaces must be replaced by escape characters {{ic|\}} followed by the 3 digit octal code {{ic|040}}:
  
By default, a tmpfs partition has its maximum size set to half your total RAM, but this can be customized. Note that the actual memory/swap consumption depends on how much you fill it up, as tmpfs partitions don't consume any memory until it is actually needed.
+
{{hc|/etc/fstab|2=
 +
UUID=47FA-4071    /home/username/Camera<font color="grey">\040</font>Pictures  vfat  defaults,noatime      0  0
 +
/dev/sda7          /media/100<font color="grey">\040</font>GB<font color="grey">\040</font>(Storage)      ext4  defaults,noatime,user  0  2
 +
}}
  
To use tmpfs for /tmp, add this line to /etc/fstab:
+
=== atime options ===
tmpfs /tmp      tmpfs defaults,nodev,nosuid,mode=1777                0 0
 
  
You may or may not want to specify the size here, but you should leave the {{Codeline|mode}} option alone in these cases to ensure that they have the correct permissions. In the example above, /tmp will be set to use up to half of your total RAM. To explicitly set a maximum size, use the {{Codeline|size}} mount option:
+
Below atime options can impact drive performance.
tmpfs /tmp      tmpfs defaults,nodev,nosuid,mode=1777,size=2G        0 0
 
  
See the '''mount''' command man page for more information.
+
* The {{ic|strictatime}} 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 {{ic|strictatime}} option is that even reading a file from the page cache (reading from memory instead of the drive) will still result in a write!
  
Reboot for the changes to take effect. Note that although it may be tempting to simply run ''mount -a'' to make the changes effective immediately,  this will make any files currently residing in these directories inaccessible (this is especially problematic for running programs with lockfiles, for example). However, if all of them are empty, it should be safe to run ''mount -a'' instead of rebooting (or mount them individually).
+
* The {{ic|noatime}} 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.
  
After applying changes, you may want to verify that they took effect with df (df -h in this case):
+
* The {{ic|nodiratime}} option disables the writing of file access times only for directories while other files still get access times written.
tmpfs                2.0G  20K  2.0G  1% /tmp
+
: {{Note|{{ic|noatime}} implies {{ic|nodiratime}}. [http://lwn.net/Articles/244941/ You do not need to specify both].}}
  
To use tmpfs for /var/lock and /var/run, you can simply symlink them to /run. Make sure to close anything important before doing this, because you will have to reboot, and daemons may not stop cleanly.
+
* {{ic|relatime}} 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 {{ic|defaults}} option, {{ic|atime}} option (which means to use the kernel default, which is {{ic|relatime}}; see {{man|8|mount}} and [[wikipedia:Stat (system call)#Criticism of atime]]) or no options at all are specified.
  
{{Note|Arch will likely do this by default in the future. See https://bugs.archlinux.org/task/18157}}
+
When using [[Mutt]] or other applications that need to know if a file has been read since the last time it was modified, the {{ic|noatime}} option should not be used; using the {{ic|relatime}} option is acceptable and still provides a performance improvement.
{{Warning|Some daemons still have files and/or directories installed into /var/lock and /var/run, and the /etc/rc.d/ scripts may need to be edited for them to work.}}
 
  
{{Cli|<nowiki># ln -sf /run/lock /var/lock
+
Since kernel 4.0 there is another related option:
# ln -sf /run /var/run
 
# reboot</nowiki>}}
 
  
=== Dealing with paths that contain spaces ===
+
* {{ic|lazytime}} 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.}}
  
You can use the escape character followed by the 3 digit octal code for space "\040".
+
Note that the {{ic|lazytime}} option works '''in combination''' with the aforementioned {{ic|*atime}} options, not as an alternative. That is {{ic|relatime}} by default, but can be even {{ic|strictatime}} with the same or less cost of disk writes as the plain {{ic|relatime}} option.
  
<pre>
+
=== Remounting the root partition ===
/dev/sda7                /home/username/Camera\040Picures  ext4  defaults,noatime      0  2
 
UUID=7D4500B3071E18B2    /media/100\040GB\040(Storage)      ntfs  defaults,noatime,user  0  0
 
</pre>
 
  
===External drives===
+
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:
External drives that are to be mounted when present but ignored if absent may require the {{Codeline|nofail}} option.  This prevents errors being reported at boot.
 
  
  /dev/sdg1    /media/backup    jfs    defaults,nofail    0  2
+
  # mount -o remount,rw /
  
==Related==
+
== See also ==
*[[Persistent block device naming]]
 
*[[Writing on a FAT32 partition as a normal user]]
 
*[[NTFS Write Support]]
 
*[[Firefox Ramdisk]]
 
*[[Using tmpfs for /var/*]]
 
  
== Resources ==
+
* [http://www.kernel.org/pub/linux/docs/lanana/device-list/devices-2.6.txt Full device listing including block device]
* [http://www.kernel.org/pub/linux/docs/device-list/devices.txt Full device listing including block device]
 
 
* [http://www.pathname.com/fhs/2.2/index.html Filesystem Hierarchy Standard]
 
* [http://www.pathname.com/fhs/2.2/index.html Filesystem Hierarchy Standard]
* [http://www.askapache.com/web-hosting/super-speed-secrets.html 30x Faster Web-Site Speed] (Detailed tmpfs)
+
* [http://www.askapache.com/optimize/super-speed-secrets/ 30x Faster Cache and Site Speed with TMPFS]
 +
* [[Samba#As_mount_entry|Adding Samba shares to /etc/fstab]]

Latest revision as of 08:50, 10 September 2017

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 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 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).
Tip: The auto type lets the mount command guess what type of file system is used. This is useful for optical media (CD/DVD).
Note: If the root file system is btrfs, the fsck order should be set to 0 instead of 1.

All specified devices within /etc/fstab will be automatically mounted on startup and when the -a flag is used with mount(8) unless the noauto option is specified. Devices that are listed and not present will result in an error unless the nofail option is used.

See fstab(5) for details.

Identifying filesystems

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

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
Note: If any of your fields contains spaces, see #Filepath spaces.

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
Tip: If you would like to return just the UUID of a specific partition: $ lsblk -no UUID /dev/sda2

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
Note: If any of your fields contains spaces, see #Filepath spaces.

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.

Note: This will make your /home filesystem type autofs, which is ignored by mlocate by default. The speedup of automounting /home may not be more than a second or two, depending on your system, so this trick may not be worth it.

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.

Note: If you intend to use the exec flag with automount, you should remove the user flag 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:

/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 strictatime 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 strictatime 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 noatime 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 nodiratime 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.
  • relatime 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 defaults option, atime option (which means to use the kernel default, which is relatime; 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:

  • lazytime 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 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.

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 /

See also