L in u X ba sics for h acke rs g e t t I n g s t a r t e d w I t h

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linuxbasicsforhackers

List Block Devices and Information with lsblk

Character and Block Devices
Something else to note about the naming of device files in the /dev direc-
tory is that the first position contains either c or b. You can see this in List-
ing 10-1 at the start of most of the entries, and it looks something like this:
crw------- 1 root root 10, 175 May 16 12:44 agpgart
These letters represent the two ways that devices transfer data in and
out. The c stands for character, and these devices are known, as you might
expect, as character devices. External devices that interact with the system
by sending and receiving data character by character, such as mice or key-
boards, are character devices.
The b stands for the second type: block devices. They communicate in
blocks of data (multiple bytes at a time) and include devices like hard drives
and DVD drives. These devices require higher-speed data throughput and
therefore send and receive data in blocks (many characters or bytes at a
time). Once you know whether a device is a character or block device, you
can easily get more information about it, as you’ll see next.
List Block Devices and Information with lsblk
The Linux command
lsblk
, short for list block, lists some basic information
about each block device listed in /dev. The result is similar to the output
from
fdisk -l
, but it will also display devices with multiple partitions in a
kind of tree, showing each device with its partitions as branches, and does
not require root privileges to run. In Listing 10-3, for example, we see sda,
with its branches sda1, sda2, and sda5.
kali >
lsblk
Name MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
fd0 2:0 1 4K 0 disk
sda1 8:0 0 20G 0 disk
|-sda1 8:1 0 18.7G 0 part /
|-sda2 8:2 0 1K 0 part
|-sda5 8:5 0 1.3G 0 part [SWAP]

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Chapter 10
sdb 8:16 1 29.8G 0 disk
|-sdb1 8.17 1 29.8G 0 disk /media
sr0 11:0 1 2.7G 0 rom
Listing 10-3: Listing block device information with
lsblk
The output may include the floppy drive as fd0 and DVD drive as sr0,
even though neither is on my system—this is simply a holdover from legacy
systems. We can also see information on the mount point of the drive—this is
the position at which the drive was attached to the filesystem. Note that the
hard drive sda1 is mounted at / and the flash drive is mounted at /media.
You’ll see more on the significance of this in the next section.

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