lpic1book

104.3 Control mounting and unmounting of filesystems

weight: 3

Candidates should be able to configure the mounting of a filesystem.

  • Manually mount and unmount filesystems.
  • Configure filesystem mounting on bootup.
  • Configure user mountable removable filesystems.
  • Use of labels and UUIDs for identifying and mounting file systems.

  • Awareness of systemd mount units.

  • /etc/fstab

  • /media/
  • mount
  • umount
  • blkid
  • lsblk

Mounting and Unmounting

When we have a formatted partition and need to use it, we have to mount it somewhere in the Linux directory hierarchy. Unlike Windows, the new driver do now show up as separated disks, but like virtual subdirectories somewhere in your / tree.

Say we want to mount the /dev/sda3 on /media/mydisk. The directory /media/mydisk should be there and then, we just run:

sudo mount -t ext4 /dev/sda3 /media/mydisk

All files and folders in /dev/sda3 will be accessible from /media/mydisk.

Run mount with no parameter to see all mounted devices. To un mount, simply use the umount on the drive or the directory. These two are equivalent:

sudo umount /dev/sda3
sudo umount /media/mydisk

Mounting and umounting can happen on many different storage types, for example on NFS storages, ISO (with -o loop), tmpfs, ...

swap disks do not need mounting. You should use swapon and swapoff to use them.

mount -t ext4 /dev/sda1 /media

The -t switch indicates the type of the filesystem .

mount -o remount,ro /dev/sda1

The -o switch passes some options (say ro for readonly)

It's usually used as one-line command:

mount -t ext4 -o remount,ro /dev/sda1 /media

The /media and /mnt directories are used to mount filesystems, even though you can use any directory for this purpose.

UUID & Labels

As you already know, there is a problem when working with classical device names like /dev/vdb1: they change! The current /dev/sdb might be seen as /dev/sdd after you remove / reconnect it. To solve this, its better to work with UUIDs (Universal Unique Identifiers). Check them with lsblk ( -O will show all available columns or specify with -o as below) and blkid.

# lsblk -o +UUID
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS                             UUID
sr0     11:0    1  1.8G  0 rom  /run/media/jadi/Fedora-WS-Live-35_B-1-2 2021-09-22-21-47-34-00
zram0  251:0    0  1.9G  0 disk [SWAP]                                  
vda    252:0    0   20G  0 disk                                         
├─vda1 252:1    0  600M  0 part /boot/efi                               E13A-EF36
├─vda2 252:2    0    1G  0 part /boot                                   19ed96a1-3b36-4202-81bb-349f7adfb8b1
└─vda3 252:3    0 18.4G  0 part /home                                   076766a5-8864-4e35-a632-464b03396f7a
                                /                                       
vdb    252:16   0    2G  0 disk                                         
└─vdb1 252:17   0    2G  0 part /tmp/lkj                                4c1a51e6-47bf-4a34-84a2-87027c91e14a

# blkid
/dev/vdb1: UUID="4c1a51e6-47bf-4a34-84a2-87027c91e14a" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="5415e516-01"
/dev/sr0: BLOCK_SIZE="2048" UUID="2021-09-22-21-47-34-00" LABEL="Fedora-WS-Live-35_B-1-2" TYPE="iso9660"
/dev/zram0: LABEL="zram0" UUID="e459f522-1675-40d2-b318-51d9bd16d7bb" TYPE="swap"
/dev/vda2: UUID="19ed96a1-3b36-4202-81bb-349f7adfb8b1" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="5f4ee154-3ade-4af6-8809-6d90d5827d39"
/dev/vda3: LABEL="fedora_localhost-live" UUID="076766a5-8864-4e35-a632-464b03396f7a" UUID_SUB="a4340a29-6d9b-4c28-a7c8-b4aab5d08893" BLOCK_SIZE="4096" TYPE="btrfs" PARTUUID="a46e64aa-65ef-4a62-9bf8-96fd19aee353"
/dev/vda1: UUID="E13A-EF36" BLOCK_SIZE="512" TYPE="vfat" PARTLABEL="EFI System Partition" PARTUUID="a7a2b260-0302-45bc-a4db-42bd2e0ee7f2"

# blkid /dev/vdb1
/dev/vdb1: UUID="4c1a51e6-47bf-4a34-84a2-87027c91e14a" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="5415e516-01"

# mount UUID="4c1a51e6-47bf-4a34-84a2-87027c91e14a" /media/mydisk/

fstab

For automatic mounting, Linux uses the /etc/fstab file. Its like a table which shows what file system should be mounted where during the boot. This is my the /etc/fstab of my Fedora:

# cat /etc/fstab

#
# /etc/fstab
# Created by anaconda on Wed Oct 20 13:16:38 2021
#
# Accessible filesystems, by reference, are maintained under '/dev/disk/'.
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info.
#
# After editing this file, run 'systemctl daemon-reload' to update systemd
# units generated from this file.
#
UUID=076766a5-8864-4e35-a632-464b03396f7a /                       btrfs   subvol=root,compress=zstd:1 0 0
UUID=19ed96a1-3b36-4202-81bb-349f7adfb8b1 /boot                   ext4    defaults        1 2
UUID=E13A-EF36          /boot/efi               vfat    umask=0077,shortname=winnt 0 2
UUID=076766a5-8864-4e35-a632-464b03396f7a /home                   btrfs   subvol=home,compress=zstd:1 0 0

These are the columns:

  • file system: Label, UUID, device
  • mount point: swap or none for swap
  • type: can be ext4 , xfs ,nfs or other types of filesystem
  • options: defaults, rw / ro, noauto, user, exec / noexec, noatime, umask
  • dump: do dump command backup this? mostly 0
  • pass: Non-zero values of pass specify the order of checking filesystems at boot time

note:

  • User-mounted filesystems default to noexec unless exec is specified after user.
  • noatime will disable recording of access times. Not using access times may improve performance.

Systemd mount units

When using systemd, a unit configuration file whose name ends in ".mount" encodes information about a file system mount point controlled and supervised by systemd.

← 104.2 Maintain the integrity of filesystems
Chapter List
 104.4 Removed →

Category

LPIC1

Contact