Forgotten Unix Commands: lsblk

UNIX and its various flavours have a lot of commands that every admin uses on a near permanent basis, such as ls, cp, cat, grep, mv, rm, gzip, tar, and so on.

Today, however, we are starting a series titled ‘Forgotten Unix Commands‘. These can come in very handy, and they often produce effects like “oh, I didn’t know you could do that on Linux!”. Such commands can brighten up the day of every dedicated server or virtual private server administrator. One of these commands is lsblk.

lsblk lists information about all or the specified block devices. The lsblk command reads the sysfs filesystem to gather information.

The command prints all block devices (except RAM disks) in a tree-like format by default.

This command can be very useful to check how the different partitions and/or disks are mounted in the system, following is an example of a desktop computer:

$ lsblk
NAME    MAJ:MIN RM   SIZE RO TYPE   MOUNTPOINT
sda       8:0    0 465.8G  0 disk
├─sda1    8:1    0  46.6G  0 part   /
├─sda2    8:2    0     1K  0 part
├─sda5    8:5    0   3.7G  0 part   [SWAP]
└─sda6    8:6    0 415.5G  0 part
sdb       8:16   0 465.8G  0 disk
└─sdb1    8:17   0 465.8G  0 part
  └─md0   9:0    0 465.7G  0 raid10 /data
sdc       8:32   0 465.8G  0 disk
└─sdc1    8:33   0 465.8G  0 part
  └─md0   9:0    0 465.7G  0 raid10 /data
sdd       8:48   1  14.9G  0 disk
└─sdd1    8:49   1  14.9G  0 part   /media/mnt/KINGSTON
sr0      11:0    1  1024M  0 rom

From this output you can see that on this desktop we have the following disks:

SDA is the fist “scsi” disk, in our case a SATA disk. On this disk the first partition is used for the / filesystem, the second partition is an extended partition, the third is a swap partition, and the last one (sda6) is used for /home, it’s a BTRFS filesystem, which the command doesn’t recognise it, though.

SDB and SDC are the two disks that are used in a RAID 10 setup, and the filesystem is mounted as /data.

SDD is a 16GB USB stick mounted under the directory /media/mnt/KINGSTON

Another example, this time output from a server with LVM:

$ lsblk
NAME                       MAJ:MIN RM   SIZE RO MOUNTPOINT
sda                          8:0    0 298.1G  0
├─sda1                       8:1    0   500M  0 /boot
└─sda2                       8:2    0 297.6G  0
  ├─vg_main-lv_swap (dm-0) 253:0    0   5.8G  0 [SWAP]
  ├─vg_main-lv_root (dm-1) 253:1    0    50G  0 /
  └─vg_main-lv_home (dm-2) 253:2    0 241.8G  0
    └─home (dm-3)          253:3    0 241.8G  0 /home
sr0                         11:0    1  1024M  0

As you can see, the command is easy to use, and the output is rather nifty with its tree style: on a glance you can see the partition layout, logical volumes, and other, additional useful information about your disks.

As opposed to lsblk, the better known fdisk -l gives similar data, however, it requires root privileges and does not recognise dm or lvm partitions.

 

This article was originally published on linuxaria. Castlegem has permission to republish. Thank you, linuxaria!

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