mount and fstab in Linux: Drives That Persist

A filesystem must be mounted — attached to a directory in the tree — before its files exist as far as the system is concerned. mount does that by hand; /etc/fstab is the table that makes it happen automatically on every boot, with the same options every time.

Mounting by hand #

Attach a device to a directory

$ sudo mount /dev/sdb1 /mnt/backup
$ mount | grep sdb1        # confirm: device, mountpoint, type, options
$ sudo umount /mnt/backup  # detach — note: u-n-mount, not unmount

The mountpoint must exist first (mkdir), and the device must not be in use — lsof finds whoever is holding it when umount says "busy".

Today's systems mount by label or UUID, not device name, because /dev/sdb1 can become /dev/sdc1 after reboot:

Identify filesystems by UUID

$ lsblk -f
sdb1  ext4  4a9c...  /mnt/backup
$ sudo mount UUID=4a9c-... /mnt/backup

fstab: the permanent record #

Every line is: what, where, type, options, dump, pass:

/etc/fstab

UUID=4a9c-...  /mnt/backup  ext4  defaults,noatime  0  2

After editing, prove it boots before rebooting — this command mounts everything fstab knows about, exactly as boot would:

Test fstab without rebooting

$ sudo mount -a

Silence means success. The options column earns its space: noatime skips access-time writes, nofail keeps booting when the disk is absent, ro mounts read-only.

Option	Effect
`defaults`	rw, suid, dev, exec, auto, nouser
`noatime`	Do not record access times (less wear)
`nofail`	Boot continues if the disk is missing
`ro`	Read-only
`x-systemd.automount`	Mount on first access, not at boot

For sizing and filesystem choices, see df and du and ext4 vs btrfs. The terminal notes series continues on the journal.