Understanding /etc/fstab

The /etc/fstab file is your Linux system's filesystem configuration table that tells your machine which storage devices (hard drives, partitions, USB drives) to mount and where to mount them when the system boots up.

• The kernel reads this file during boot time to automatically mount all partitions to the Linux filesystem​.
• While the mount command provides temporary mounting (lost after restart), /etc/fstab enables permanent mounting that survives reboots​.
• This file is read by programs but only written by the system administrator, it's not meant to be edited by regular users​.
• Each line describes one filesystem, and the file contains static information (not dynamically updated) about all available disks and partitions​.
• Every entry has exactly six fields separated by spaces or tabs, each serving a specific purpose​.

Example:

Here's a simple /etc/fstab to understand the structure:

# /etc/fstab
UUID=4d028ac1-d413-4d3a-94b4-251db287744f  /           ext4  defaults    1  1
UUID=c13ef520-fac6-49b5-8717-1afd49097ef4  /boot       ext4  defaults    1  2
UUID=5010a5d7-9457-4a44-85c7-d836b39e06a2  /home       ext4  defaults    0  2
UUID=498ae307-b89e-47ac-b1fb-293c2342d417  swap        swap  defaults    0  0

Breaking down the first line:​

• UUID: Uniquely identifies the partition.
• /: This mounts to the root directory (the main filesystem).
• ext4: The partition uses ext4 filesystem format.
• defaults: Use standard mount settings.
• 1: Run dump on this filesystem.
• 1: Check this filesystem first during boot (root filesystem priority).

Syntax and Field Breakdown

Each line in /etc/fstab follows this pattern:​

<Device>  <Mount Point>  <File System Type>  <Mount Options>  <Dump>  <Fsck Order>

Let's understand each field:​

Mount Options

Field 4 has several important options you'll encounter:​

• rw = Read-Write access; ro = Read-Only access
• auto = Mount automatically at boot; noauto = Mount only when explicitly requested
• defaults = Use standard options (rw, suid, dev, exec, auto, nouser, async)
• exec = Allow executing programs; noexec = Prevent execution
• sync = Write changes immediately; async = Write changes asynchronously

Adding a New External Drive

Let's say you want to add a USB drive permanently. Here's how an entry would look:

/dev/sdc1  /novi_disk  ext3  defaults  0  2

This means:

• Mount the first partition of the third disk (/dev/sdc1)
• At the mount point /novi_disk (you must create this folder first)
• Using ext3 filesystem
• With default options
• No dump backup needed
• Check this disk during boot (but after the root filesystem)

Special Case: Swap Space

Swap is virtual memory on disk:​

UUID=498ae307-b89e-47ac-b1fb-293c2342d417  swap  swap  defaults,pri=1  0  0

Here, the mount point is literally the word "swap" because swap doesn't have a traditional mount point.

Fsck Order Values Explained:​

• Root filesystem (/): Always use 1
• Other filesystems: Use 2 if you want them checked
• Skip checking: Use 0 (useful for swap, USB drives)

Dump Field: Most students can safely ignore this field and use 0. The dump program is rarely used in modern systems.

Testing Before Rebooting

After editing /etc/fstab, test your changes with:

sudo mount -a

This applies all entries in /etc/fstab without rebooting, helping you catch errors before they cause boot problems.

Common Mount Options Combinations

Here are realistic examples we might encounter:

The /etc/fstab file is essential for Linux system administration because it defines how your storage devices integrate into your filesystem automatically. Always remember: test changes with mount -a before rebooting, and use UUIDs instead of device names for reliability.