fstab

LINUXLPIC1-101

Warning: These examples may crash your computer if there is something incorrect. For example, setting the wrong UUID in /etc/fstab will make the system crash or unbootable. Ensure you put the correct values in the /etc/fstab file. The author is not responsible for any damage. It is also recommended to always create a backup of the fstab file before any editing.

tl;dr

The fstab file has 6 fields:

  1. The device (/dev/sda1, UUID or label)

  2. The mount point (/home)

  3. The FS type (ext4)

  4. The options (defaults, ro, user, noauto) defaults= rw, suid, dev, exec, auto, nouser, async.

  5. The dump (backup) 0

  6. fsck (0=none, 1=root, 2=other FS)

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The /etc/fstab (file system table) file is a critical configuration file in Linux that tells the system how to mount partitions and storage devices automatically during boot.

It consists of six fields, separated by tabs or spaces.

The 6 Fields of /etc/fstab

Field Name Description Example

1 Device The identifier for the partition (UUID, Label, or /dev path). UUID=123-abc

2 Mount Point The directory where the filesystem will be attached. /home

3 FS Type The type of filesystem (ext4, xfs, btrfs, vfat, ntfs-3g, swap). ext4

4 Options Specific mount settings (comma-separated, no spaces). defaults,ro

5 Dump Used by the dump utility (0 = skip, 1 = backup). 0

6 FSCK The order in which fsck checks the disk (0=none, 1=root, 2=others). 2

Detailed Breakdown
1. Device (The "What")

While you can use /dev/sda1, modern systems prefer UUID (Universally Unique Identifier). You can also use the LABEL, however using the UUID is preferred and more reliable. Using the UUID ensures that even if you move the hard drive to a different SATA port, the system still finds the correct partition. The UUID is automatically generated when you format a disk. There is a risk that two filesystems have the same Label, hence causing an undefined behavior.

2. Mount Point (The "Where")

This is the directory where the files will appear.

  • Note: For swap partitions, this field is simply written as none or swap.

3. Filesystem Type

Common types include:

  • ext2/ext3/ext4

  • xfs

  • btrfs

  • vfat: Used for EFI partitions or USB sticks.

  • nfs: For network-attached storage.

4. Mount Options

The defaults option typically includes rw, suid, dev, exec, auto, nouser, and async. Other important flags:

  • noauto: The partition is not mounted at boot (only when you manually run mount).

  • user: Allows a non-root user to mount the drive.

  • ro: Mounts the filesystem as Read-Only.

5. Dump (The "Backup")

This is rarely used today. It’s almost always 0 (do not back up).

6. FSCK (The "Check")

This determines the priority for the filesystem check at boot:

  • 1: Reserved for the root (/) partition.

  • 2: For all other partitions.

  • 0: Do not check (used for swap or network drives).

Tips

If you modify /etc/fstab and want to test it without rebooting, run the command:

mount -a

When editing the file with vi, you may want to insert the output from a command into a file, immediately after the cursor:

:r!command

You can use this to insert the UUID of a disk so you don't have to copy that long string. You can execute something like this:

:r!sudo blkid | grep sr0

Then you can edit the line and remove the unwanted parts.

Contact

Email

hello@unixtips.eu

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