Mount and fstab Basics - How to Attach Filesystems in Linux

2026-06-01 Reading time: About 12 min Difficulty: Intermediate

What You'll Learn

• What "mounting" means in Linux and how it works
• How to manually mount a USB drive or additional disk
• How to read and write /etc/fstab for persistent mounts
• Why UUID is safer than device names like /dev/sdb1
• How to safely unmount a device

What Is Mounting?

In Linux, you cannot access a storage device until it is mounted. Mounting attaches the device to a directory in the filesystem tree, making its contents accessible at that path.

/                    ← root filesystem (mounted at /)
├── home/            ← separate partition mounted at /home
├── mnt/
│   └── usb/         ← USB drive mounted here becomes browsable
└── var/

Unlike Windows drive letters (C:, D:), Linux integrates all devices into a single directory tree. The directory where a device is attached is called the mount point.

How to Check What Is Currently Mounted

Use findmnt for a clean tree view, or mount for the traditional listing.

$ findmnt

TARGET                  SOURCE     FSTYPE     OPTIONS
/                       /dev/sda1  ext4       rw,relatime
├─/sys                  sysfs      sysfs      rw,nosuid,nodev,noexec
├─/proc                 proc       proc       rw,nosuid,nodev,noexec
├─/dev                  udev       devtmpfs   rw,nosuid
├─/run                  tmpfs      tmpfs      rw,nosuid,nodev
└─/home                 /dev/sda2  ext4       rw,relatime

Check a specific mount point:

$ findmnt /home
TARGET  SOURCE     FSTYPE  OPTIONS
/home   /dev/sda2  ext4    rw,relatime

How to Find Device Names and UUIDs

Before mounting, identify your target device.

$ lsblk

NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
sda      8:0    0   20G  0 disk
├─sda1   8:1    0   19G  0 part /
└─sda2   8:2    0    1G  0 part /home
sdb      8:16   1    8G  0 disk
└─sdb1   8:17   1    8G  0 part

sdb1 has no MOUNTPOINTS entry — it is not yet mounted.

Get the UUID for a device:

$ sudo blkid

/dev/sda1: UUID="a1b2c3d4-1111-2222-3333-444455556666" TYPE="ext4"
/dev/sda2: UUID="b2c3d4e5-2222-3333-4444-555566667777" TYPE="ext4"
/dev/sdb1: UUID="c3d4e5f6-3333-4444-5555-666677778888" TYPE="vfat"

For a single device:

$ sudo blkid /dev/sdb1
/dev/sdb1: UUID="c3d4e5f6-3333-4444-5555-666677778888" TYPE="vfat"

How to Mount a Device Manually

Create a mount point directory first, then run mount.

# Create the mount point
$ sudo mkdir -p /mnt/usb

# Mount (filesystem type auto-detected)
$ sudo mount /dev/sdb1 /mnt/usb

# Verify
$ findmnt /mnt/usb
TARGET    SOURCE     FSTYPE  OPTIONS
/mnt/usb  /dev/sdb1  vfat    rw,relatime

Specify the filesystem explicitly with -t:

$ sudo mount -t ext4 /dev/sdb1 /mnt/data
$ sudo mount -t vfat /dev/sdb1 /mnt/usb
$ sudo mount -t ntfs /dev/sdb1 /mnt/win

Common mount options (-o):

# Mount read-only
$ sudo mount -o ro /dev/sdb1 /mnt/usb

# Switch to read-write without unmounting
$ sudo mount -o remount,rw /mnt/usb

How to Unmount a Device

Always unmount before physically removing a device. This flushes write buffers and prevents data corruption.

$ sudo umount /mnt/usb

# Or specify the device
$ sudo umount /dev/sdb1

# Find which process is using the mount
$ lsof /mnt/usb

What Is /etc/fstab?

/etc/fstab (filesystem table) defines which devices to mount automatically at boot. Every entry in this file is processed during startup.

$ cat /etc/fstab

# <file system>     <mount point>  <type>  <options>  <dump>  <pass>
UUID=a1b2c3d4-...   /             ext4    defaults   0       1
UUID=b2c3d4e5-...   /home         ext4    defaults   0       2
UUID=f9g0h1i2-...   none          swap    sw         0       0

How to Write an fstab Entry

Each line has six space-separated fields:

Example entry for an ext4 data partition:

UUID=c3d4e5f6-3333-4444-5555-666677778888  /mnt/data  ext4  defaults  0  2

Why Use UUID Instead of Device Names?

Device names like /dev/sdb depend on the order the kernel detects drives. After adding, removing, or reordering disks, the same physical drive may get a different name. UUID never changes.

# Risky — device name can change after reboot
/dev/sdb1  /mnt/data  ext4  defaults  0  2

# Safe — UUID is permanent
UUID=c3d4e5f6-3333-4444-5555-666677778888  /mnt/data  ext4  defaults  0  2

How to Make a Mount Persistent with fstab

Step-by-step: add a second disk or USB drive so it auto-mounts on every boot.

# 1. Get the UUID
$ sudo blkid /dev/sdb1
/dev/sdb1: UUID="c3d4e5f6-3333-4444-5555-666677778888" TYPE="ext4"

# 2. Create the mount point
$ sudo mkdir -p /mnt/data

# 3. Edit fstab
$ sudo nano /etc/fstab

Add this line:

UUID=c3d4e5f6-3333-4444-5555-666677778888  /mnt/data  ext4  defaults  0  2

# 4. Test without rebooting
$ sudo mount -a

# 5. Verify
$ findmnt /mnt/data
TARGET     SOURCE     FSTYPE  OPTIONS
/mnt/data  /dev/sdb1  ext4    rw,relatime