lsblk Command Linux: Complete Guide to List and Manage Block Devices

The lsblk command is an essential Linux utility that displays information about block devices in a tree-like format. Whether you’re a system administrator managing storage devices or a Linux user trying to understand your system’s storage configuration, mastering lsblk is crucial for effective storage management.

What is the lsblk Command?

lsblk stands for “list block devices” and is part of the util-linux package. It reads the sysfs filesystem and udev database to gather information about block devices, presenting them in an easy-to-understand hierarchical structure. Unlike other storage-related commands, lsblk shows the relationship between devices and their partitions clearly.

Basic Syntax and Usage

The basic syntax of the lsblk command is:

lsblk [options] [device...]

When executed without any arguments, lsblk displays all available block devices:

$ lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda      8:0    0   20G  0 disk 
├─sda1   8:1    0  500M  0 part /boot
├─sda2   8:2    0    2G  0 part [SWAP]
└─sda3   8:3    0 17.5G  0 part /
sdb      8:16   0    5G  0 disk 
└─sdb1   8:17   0    5G  0 part /home
sr0     11:0    1 1024M  0 rom

Understanding the Output Columns

The default lsblk output includes several important columns:

• NAME: Device name (e.g., sda, sdb1)
• MAJ:MIN: Major and minor device numbers
• RM: Whether the device is removable (1 = yes, 0 = no)
• SIZE: Size of the device
• RO: Whether the device is read-only (1 = yes, 0 = no)
• TYPE: Device type (disk, part, lvm, etc.)
• MOUNTPOINT: Where the device is mounted

Essential lsblk Command Options

Display All Devices (-a)

By default, lsblk hides empty devices. Use the -a option to show all devices:

$ lsblk -a
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda      8:0    0   20G  0 disk 
├─sda1   8:1    0  500M  0 part /boot
├─sda2   8:2    0    2G  0 part [SWAP]
└─sda3   8:3    0 17.5G  0 part /
sdb      8:16   0    5G  0 disk 
└─sdb1   8:17   0    5G  0 part /home
sr0     11:0    1 1024M  0 rom
loop0    7:0    0     0B  0 loop
loop1    7:1    0     0B  0 loop

Show Filesystem Information (-f)

The -f option displays filesystem information:

$ lsblk -f
NAME   FSTYPE LABEL UUID                                 MOUNTPOINT
sda                                                      
├─sda1 ext4         a1b2c3d4-e5f6-7890-abcd-ef1234567890 /boot
├─sda2 swap         12345678-90ab-cdef-1234-567890abcdef [SWAP]
└─sda3 ext4         fedcba09-8765-4321-fedc-ba0987654321 /
sdb                                                      
└─sdb1 ext4   DATA  abcdef12-3456-7890-abcd-ef1234567890 /home

Output in JSON Format (-J)

For programmatic use, the -J option outputs information in JSON format:

$ lsblk -J
{
   "blockdevices": [
      {
         "name": "sda",
         "maj:min": "8:0",
         "rm": false,
         "size": "20G",
         "ro": false,
         "type": "disk",
         "mountpoint": null,
         "children": [
            {
               "name": "sda1",
               "maj:min": "8:1",
               "rm": false,
               "size": "500M",
               "ro": false,
               "type": "part",
               "mountpoint": "/boot"
            }
         ]
      }
   ]
}

Show Only Specific Columns (-o)

Use the -o option to display only specific columns:

$ lsblk -o NAME,SIZE,TYPE,MOUNTPOINT
NAME   SIZE TYPE MOUNTPOINT
sda     20G disk 
├─sda1 500M part /boot
├─sda2   2G part [SWAP]
└─sda3 17.5G part /
sdb      5G disk 
└─sdb1   5G part /home

No Tree Format (-l)

The -l option displays devices in list format instead of tree format:

$ lsblk -l
NAME MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda    8:0    0   20G  0 disk 
sda1   8:1    0  500M  0 part /boot
sda2   8:2    0    2G  0 part [SWAP]
sda3   8:3    0 17.5G  0 part /
sdb    8:16   0    5G  0 disk 
sdb1   8:17   0    5G  0 part /home

Advanced lsblk Usage Examples

Display Block Device Topology (-t)

Show information about block device topology:

$ lsblk -t
NAME   ALIGNMENT MIN-IO OPT-IO PHY-SEC LOG-SEC ROTA SCHED    RQ-SIZE
sda            0    512      0     512     512    1 deadline     128
├─sda1         0    512      0     512     512    1            128
├─sda2         0    512      0     512     512    1            128
└─sda3         0    512      0     512     512    1            128

Show Device Permissions (-m)

Display device ownership and permissions:

$ lsblk -m
NAME   SIZE OWNER GROUP MODE
sda     20G root  disk  brw-rw----
├─sda1 500M root  disk  brw-rw----
├─sda2   2G root  disk  brw-rw----
└─sda3 17.5G root  disk  brw-rw----

Filter by Device Type

You can specify particular devices to examine:

$ lsblk /dev/sda
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda      8:0    0   20G  0 disk 
├─sda1   8:1    0  500M  0 part /boot
├─sda2   8:2    0    2G  0 part [SWAP]
└─sda3   8:3    0 17.5G  0 part /

Working with Different Storage Types

LVM Logical Volumes

When working with LVM, lsblk shows the relationship between physical volumes, volume groups, and logical volumes:

$ lsblk
NAME               MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda                  8:0    0   20G  0 disk 
├─sda1               8:1    0  500M  0 part /boot
└─sda2               8:2    0 19.5G  0 part 
  ├─vg01-root      253:0    0   15G  0 lvm  /
  └─vg01-swap      253:1    0  4.5G  0 lvm  [SWAP]

RAID Devices

For software RAID arrays, lsblk displays the RAID structure:

$ lsblk
NAME    MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
sda       8:0    0   10G  0 disk  
└─sda1    8:1    0   10G  0 part  
  └─md0   9:0    0   20G  0 raid1 /
sdb       8:16   0   10G  0 disk  
└─sdb1    8:17   0   10G  0 part  
  └─md0   9:0    0   20G  0 raid1 /

Practical Use Cases

System Administration Tasks

1. Quick Storage Overview:

$ lsblk -f -o NAME,SIZE,FSTYPE,MOUNTPOINT
NAME   SIZE FSTYPE MOUNTPOINT
sda     20G        
├─sda1 500M ext4   /boot
├─sda2   2G swap   [SWAP]
└─sda3 17.5G ext4   /

2. Check Available Space:

$ lsblk -o NAME,SIZE,AVAIL,USE%,MOUNTPOINT
NAME   SIZE AVAIL USE% MOUNTPOINT
sda     20G             
├─sda1 500M  350M  25% /boot
├─sda2   2G          [SWAP]
└─sda3 17.5G  8.2G  51% /

3. Find Unmounted Devices:

$ lsblk -o NAME,SIZE,FSTYPE,MOUNTPOINT | grep -E "(part|disk)" | grep -v "/"

Troubleshooting Storage Issues

When troubleshooting storage problems, combine lsblk with other options:

# Check for read-only filesystems
$ lsblk -o NAME,RO,MOUNTPOINT

# Verify filesystem types
$ lsblk -f

# Check device topology for performance issues
$ lsblk -t

Combining lsblk with Other Commands

The lsblk command works well with other Linux utilities:

# Find devices with specific filesystem
$ lsblk -f | grep ext4

# Count total partitions
$ lsblk -l | grep part | wc -l

# Export device information to file
$ lsblk -J > devices.json

Common Options Summary

Best Practices and Tips

1. Regular Monitoring: Use lsblk regularly to monitor storage device changes and additions.
2. Script Integration: Incorporate lsblk -J in scripts for automated storage management.
3. Combine with Watch: Use watch lsblk to monitor real-time changes during device operations.
4. Documentation: Save device configurations using lsblk -f > storage-config.txt for documentation purposes.
5. Security: Use lsblk -m to verify device permissions in security audits.

Troubleshooting Common Issues

Device Not Showing: If a device doesn’t appear, check if it’s properly connected and recognized by the kernel using dmesg | tail.

Permission Denied: Some lsblk options may require root privileges. Use sudo lsblk when necessary.

Outdated Information: If the output seems outdated, try sudo partprobe to refresh the kernel’s partition table information.

Conclusion

The lsblk command is an invaluable tool for Linux system administrators and users alike. Its clear, hierarchical display of block devices makes it easy to understand storage configurations, troubleshoot issues, and manage devices effectively. By mastering the various options and combining lsblk with other Linux commands, you can efficiently manage storage systems and maintain optimal system performance.

Whether you’re setting up new storage devices, troubleshooting mounting issues, or documenting system configurations, lsblk provides the essential information you need in a format that’s both human-readable and script-friendly. Practice with these examples and explore the various options to become proficient with this essential Linux storage management tool.