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The /etc/fstab file contains static filesystem information. It defines how storage devices and partitions are to be mounted and integrated into the overall system. It is read by the
mount command to determine which options to use when mounting a specific device or partition.
- 1 File example
- 2 Field definitions
- 3 Identifying filesystems
- 4 Tips and tricks
- 5 See also
/etc/fstab, using kernel name descriptors:
# <file system> <dir> <type> <options> <dump> <pass> tmpfs /tmp tmpfs nodev,nosuid 0 0 /dev/sda1 / ext4 defaults,noatime 0 1 /dev/sda2 none swap defaults 0 0 /dev/sda3 /home ext4 defaults,noatime 0 2
/etc/fstab file contains the following fields separated by a space or tab:
<file system> <dir> <type> <options> <dump> <pass>
- <file system> - the partition or storage device to be mounted.
- <dir> - the mountpoint where <file system> is mounted to.
- <type> - the file system type of the partition or storage device to be mounted. Many different file systems are supported:
autotype lets the mount command guess what type of file system is used. This is useful for optical media (CD/DVD).
- <options> - mount options of the filesystem to be used. Note that some mount options are filesystem specific. Some of the most common options are:
auto- Mount automatically at boot, or when the command
mount -ais issued.
noauto- Mount only when you tell it to.
exec- Allow execution of binaries on the filesystem.
noexec- Disallow execution of binaries on the filesystem.
ro- Mount the filesystem read-only.
rw- Mount the filesystem read-write.
user- Allow any user to mount the filesystem. This automatically implies
nodev, unless overridden.
users- Allow any user in the users group to mount the filesystem.
nouser- Allow only root to mount the filesystem.
owner- Allow the owner of device to mount.
sync- I/O should be done synchronously.
async- I/O should be done asynchronously.
dev- Interpret block special devices on the filesystem.
nodev- Don't interpret block special devices on the filesystem.
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- Don't update inode access times on the filesystem. Can help performance (see atime options).
nodiratime- Do not update directory inode access times on the filesystem. Can help performance (see 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).
vfatoption to flush data more often, thus making copy dialogs or progress bars to stay up until all data is written.
defaults- the default mount options for the filesystem to be used. The default options for
- <dump> - used by the dump utility to decide when to make a backup. 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> - used by fsck to decide which order filesystems are to 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 have a 2. File systems with a value 0 will not be checked by the fsck utility.
There are three ways to identify a partition or storage device in
/etc/fstab: by its kernel name descriptor, label or UUID. The advantage of using UUIDs or labels is that they are not dependent on the order in which the drives are (physically) connected to the machine. This is useful if the storage device order in the BIOS is changed, or if you switch the storage device cabling. Also, sometimes the BIOS may occasionally change the order of storage devices. Read more about this in the Persistent block device naming article.
To list basic information about the partitions, run:
$ lsblk -f
NAME FSTYPE LABEL UUID MOUNTPOINT sda ├─sda1 ext4 Arch_Linux 978e3e81-8048-4ae1-8a06-aa727458e8ff / ├─sda2 ntfs Windows 6C1093E61093B594 └─sda3 ext4 Storage f838b24e-3a66-4d02-86f4-a2e73e454336 /media/Storage sdb ├─sdb1 ntfs Games 9E68F00568EFD9D3 └─sdb2 ext4 Backup 14d50a6c-e083-42f2-b9c4-bc8bae38d274 /media/Backup sdc └─sdc1 vfat Camera 47FA-4071 /media/Camera
lsblk -f to list the partitions, and prefix them with
See the example.
To label a device or partition, see this article. You can also install and use , but renaming the root partition would have to be done from a "live" Linux distribution (Parted Magic, Ubuntu, etc) because the partition needs to be unmounted first.
lsblk -f to list the partitions, and prefix them with
# <file system> <dir> <type> <options> <dump> <pass> tmpfs /tmp tmpfs nodev,nosuid 0 0 LABEL=Arch_Linux / ext4 defaults,noatime 0 1 LABEL=Arch_Swap none swap defaults 0 0
All partitions and devices have a unique UUID. They are generated by filesystem utilities (e.g.
mkfs.*) when you create or format a partition.
lsblk -f to list the partitions, and prefix them with
$ lsblk -no UUID /dev/sda2
# <file system> <dir> <type> <options> <dump> <pass> tmpfs /tmp tmpfs nodev,nosuid 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 none swap defaults 0 0
Tips and tricks
Auto mount devices
To auto mount other disks devices during a boot, do this:
lsblk -f command to list all disks devices.
copy the UUID related to device and input in
and make a new line with device informations.
$ lsblk -f
NAME FSTYPE LABEL UUID MOUNTPOINT sda ├─sda1 ext4 Arch_Linux 978e3e81-8048-4ae1-8a06-aa727458e8ff / ├─sda2 ntfs Windows 6C1093E61093B594 └─sda3 ext4 Storage f838b24e-3a66-4d02-86f4-a2e73e454336 /media/Storage
# <file system> <dir> <type> <options> <dump> <pass> tmpfs /tmp tmpfs nodev,nosuid 0 0 ... f838b24e-3a66-4d02-86f4-a2e73e454336 /media/Storage ext4 defaults 0 0 ...
remember: check the fstab man page to more info!
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
lsblk -f command. Here are some steps to assign a UUID to your swap:
Identify the swap partition:
# swapon -s
Disable the swap:
# swapoff /dev/sda7
Recreate the swap with a new UUID assigned to it:
# mkswap -U random /dev/sda7
Activate the swap:
# swapon /dev/sda7
If any mountpoint contains spaces, use the escape character
\ followed by the 3 digit octal code
040 to emulate them:
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
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.
/dev/sdg1 /media/backup jfs defaults,nofail 0 2
The use of
relatime can improve drive performance. Linux by default uses
atime, which keeps a record (writes to the drive) every time it reads anything. This is more purposeful when Linux is used for servers; it doesn't have much value for desktop use. The worst thing about the default
atime option is that even reading a file from the page cache (reading from memory instead of the drive) will still result in a write! Using 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 a rare few like Mutt that need the such information. For mutt, you should only use the
relatime option. Using the
relatime option enables the writing of file access times only when the file is being modified (unlike
noatime where the file access time will never be changed and will be older than the modification time). The
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
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.
nodiratime. You do not need to specify both.
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 /tmp, /var/lock and /var/run. Do NOT use it on /var/tmp, because that folder is meant for temporary files that are preserved across reboots. Arch uses a tmpfs
/run directory, with
/var/lock simply existing as symlinks for compatibility. It is also used for
/tmp in the default
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 do not consume any memory until it is actually needed.
To use tmpfs for
/tmp, add this line to
tmpfs /tmp tmpfs nodev,nosuid 0 0
You may or may not want to specify the size here, but you should leave the
mode option alone in these cases to ensure that they have the correct permissions (1777). 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
size mount option:
tmpfs /tmp tmpfs nodev,nosuid,size=2G 0 0
Here is a more advanced example showing how to add tmpfs mounts for users. This is useful for websites, mysql tmp files,
~/.vim/, and more. It's important to try and get the ideal mount options for what you are trying to accomplish. The goal is to have as secure settings as possible to prevent abuse. Limiting the size, and specifying uid and gid + mode is very secure. More info.
tmpfs /www/cache tmpfs rw,size=1G,nr_inodes=5k,noexec,nodev,nosuid,uid=648,gid=648,mode=1700 0 0
mount command man page for more information. One useful mount option in the man page is the
default option. At least understand that.
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).
After applying changes, you may want to verify that they took effect by looking at
/proc/mounts and using
$ findmnt --target /tmp
TARGET SOURCE FSTYPE OPTIONS /tmp tmpfs tmpfs rw,nosuid,nodev,relatime
Generally, I/O intensive tasks and programs that run frequent read/write operations can benefit from using a tmpfs folder. Some applications can even receive a substantial gain by offloading some (or all) of their data onto the shared memory. For example, relocating the Firefox profile into RAM shows a significant improvement in performance.
Improving compile times
/tmp, in this case) needs to be mounted without
noexec, else it will prevent build scripts or utilities from being executed. Also, as stated above, the default size is half of the available RAM. You may run out of space.
You can run makepkg with a tmpfs folder for the build directory (which is also a setting in
$ BUILDDIR=/tmp/makepkg makepkg
Writing to FAT32 as Normal User
To write on a FAT32 partition, you must make a few changes to your
/dev/sdxY /mnt/some_folder vfat user,rw,umask=000 0 0
user flag means that any user (even non-root) can mount and unmount the partition
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:
/dev/sda9 /mnt/fat32 vfat user,rw,umask=111,dmask=000 0 0
Remounting the root partition
If for some reason the root partition has been improperly mounted read only, remount the root partition with the following command:
# mount -o remount,rw /; #Remount the root partition with read-write access