Linux Commands - Embedded Linux Lab

What is lsblk?

The lsblk command is one of the most important Linux commands used during embedded Linux bring-up.

It helps engineers verify storage detection, partition layout, and root filesystem mounting on devices such as eMMC, SD card, and NAND-based systems.

lsblk stands for list block devices.

It is used to display information about storage devices such as:

eMMC
SD card
USB storage
NAND/NOR block devices
Partitions

In embedded Linux systems, lsblk is one of the most important commands for verifying storage detection during bring-up.

Why lsblk is important in embedded systems

During embedded Linux development, storage-related problems are very common:

SD card not detected
eMMC partitions missing
Root filesystem not mounted
Wrong partition layout
Device nodes not created

The lsblk command helps you quickly confirm:

Whether the kernel detected the storage
Partition structure
Mount points
Device hierarchy

Basic Syntax

lsblk

lsblk

This shows all the available block devices in a tree

Example Output

NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
mmcblk0 179:0 0 7.3G 0 disk
├─mmcblk0p1 179:1 0 256M 0 part /boot
└─mmcblk0p2 179:2 0 7.0G 0 part /

NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
mmcblk0 179:0 0 7.3G 0 disk
├─mmcblk0p1 179:1 0 256M 0 part /boot
└─mmcblk0p2 179:2 0 7.0G 0 part /

Understanding the output

Column	Meaning
NAME	Device name
MAJ:MIN	Major and minor device numbers
RM	Removable device
SIZE	Device or partition size
RO	Read-only flag
TYPE	disk / part
MOUNTPOINT	Where it is mounted

Common block device names in embedded Linux

Device	Meaning
mmcblk0	Primary eMMC or SD card
mmcblk0p1	Partition 1
mmcblk0p2	Partition 2
sda	USB storage
mtdblock0	NAND block device

Useful lsblk options

Show filesystem type

lsblk -f

lsblk -f

Example

NAME FSTYPE LABEL UUID MOUNTPOINT
mmcblk0p1 vfat 12AB-34CD /boot
mmcblk0p2 ext4 a1b2c3d4-e5f6 /

NAME FSTYPE LABEL UUID MOUNTPOINT
mmcblk0p1 vfat 12AB-34CD /boot
mmcblk0p2 ext4 a1b2c3d4-e5f6 /

This is extremely useful for verifying root filesystem format.

Show size in human-readable format

lsblk -h

lsblk -h

Shows sizes like MB, GB.

Show only block devices (no RAM disks)

lsblk -o NAME,SIZE,TYPE,MOUNTPOINT

lsblk -o NAME,SIZE,TYPE,MOUNTPOINT

Useful when debugging minimal rootfs

lsblk vs df vs mount

Command	Purpose
lsblk	Shows device and partition structure
df	Shows filesystem usage
mount	Shows mounted filesystems

During bring-up, lsblk is used first, then mount, then df.

Practical embedded Linux use cases

1. Verify SD card detection

After boot:

lsblk

lsblk

If mmcblk0 does not appear → kernel or device tree issue.

2. Verify partition layout

Check whether expected partitions exist:

boot
rootfs
data

lsblk

lsblk

Wrong partition table → Yocto image issue

3. Check root filesystem mount

Look at MOUNTPOINT.

If / is missing → boot argument issue.

Common issues and debugging

Issue: lsblk command not found

On minimal systems (BusyBox):

lsblk may not be enabled

Solution:

Enable util-linux in Yocto
Or enable lsblk in BusyBox config

Issue: Device visible in dmesg but not in lsblk

Possible reasons:

No partition table
Block driver not enabled
Missing udev

Check:

dmesg | grep mmc

dmesg | grep mmc

Summary

lsblk lists block devices and partitions
Essential for embedded Linux bring-up
Helps debug storage, rootfs, and boot issues
Used heavily during Yocto development
One of the first commands engineers run after boot

What to learn next

After understanding lsblk, continue with:

mount command
df command
Linux filesystem layout
Root filesystem concepts

These topics are crucial before moving to Yocto and BSP development.