Complete Guide to lsblk Command: List Block Devices

Table of Contents

Introduction

The lsblk command is a powerful utility in Linux systems that displays information about block devices in a tree-like format. Block devices are hardware components or logical constructs that store data in fixed-size blocks, such as hard drives, SSDs, USB drives, CD-ROMs, and logical volumes. This command is essential for system administrators, developers, and users who need to understand the storage hierarchy and device relationships on their systems.

The lsblk command reads information from the /sys filesystem and presents it in an easily readable format, showing the relationship between physical devices and their partitions, mount points, and various attributes.

Basic Syntax and Options

The basic syntax for the lsblk command is:

`bash lsblk [OPTIONS] [DEVICE...] `

Core Command Structure

| Component | Description | Required | |-----------|-------------|----------| | lsblk | Base command | Yes | | OPTIONS | Flags to modify output | No | | DEVICE | Specific device to examine | No |

Most Common Options

| Option | Long Form | Description | |--------|-----------|-------------| | -a | --all | Show all devices, including empty ones | | -b | --bytes | Print size in bytes | | -d | --nodeps | Don't print slaves or holders | | -f | --fs | Show filesystem information | | -h | --help | Display help message | | -J | --json | Use JSON output format | | -l | --list | Produce output in list format | | -m | --perms | Show permissions | | -n | --noheadings | Don't print headings | | -o | --output | Specify output columns | | -P | --pairs | Produce output in key="value" pairs | | -r | --raw | Use raw output format | | -S | --scsi | Show only SCSI devices | | -t | --topology | Show topology information | | -x | --sort | Sort output by specified column |

Understanding Block Devices

Types of Block Devices

Block devices in Linux can be categorized into several types:

| Device Type | Description | Example | |-------------|-------------|---------| | Physical Drives | Hard disks, SSDs | /dev/sda, /dev/nvme0n1 | | Partitions | Subdivisions of drives | /dev/sda1, /dev/sda2 | | Logical Volumes | LVM managed storage | /dev/mapper/vg-lv | | Loop Devices | File-backed block devices | /dev/loop0 | | RAM Disks | Memory-based storage | /dev/ram0 | | Optical Media | CD/DVD drives | /dev/sr0 | | USB Devices | External storage | /dev/sdb |

Device Naming Conventions

| Prefix | Device Type | Description | |--------|-------------|-------------| | sd | SCSI/SATA | Traditional hard drives and SSDs | | hd | IDE/PATA | Legacy parallel ATA drives | | nvme | NVMe | Modern NVMe SSDs | | sr | SCSI CD-ROM | Optical drives | | loop | Loop device | File-backed virtual devices | | md | Software RAID | Multi-device arrays | | dm | Device Mapper | LVM and other mapped devices |

Default Output Format

When you run lsblk without any options, it displays information in a tree format:

`bash lsblk `

Default Columns Explained

| Column | Description | Example | |--------|-------------|---------| | NAME | Device name | sda, sda1 | | MAJ:MIN | Major and minor device numbers | 8:0, 8:1 | | RM | Removable device indicator | 0 (no), 1 (yes) | | SIZE | Device size | 500G, 100M | | RO | Read-only indicator | 0 (read-write), 1 (read-only) | | TYPE | Device type | disk, part, lvm | | MOUNTPOINT | Where device is mounted | /, /home, [SWAP] |

Sample Default Output

` NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sda 8:0 0 500G 0 disk ├─sda1 8:1 0 512M 0 part /boot/efi ├─sda2 8:2 0 1G 0 part /boot └─sda3 8:3 0 498G 0 part └─ubuntu--vg-ubuntu--lv 253:0 0 249G 0 lvm / sr0 11:0 1 1024M 0 rom `

Command Options and Examples

Basic Information Display

#### Show All Devices `bash lsblk -a ` This command displays all block devices, including empty ones that are typically hidden.

#### List Format Output `bash lsblk -l ` Produces output in list format instead of tree format:

` NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sda 8:0 0 500G 0 disk sda1 8:1 0 512M 0 part /boot/efi sda2 8:2 0 1G 0 part /boot sda3 8:3 0 498G 0 part ubuntu--vg-ubuntu--lv 253:0 0 249G 0 lvm / sr0 11:0 1 1024M 0 rom `

#### Show Only Physical Devices `bash lsblk -d ` Displays only the main devices without their partitions or dependencies.

Filesystem Information

#### Display Filesystem Details `bash lsblk -f `

This shows filesystem-related information:

| Column | Description | |--------|-------------| | FSTYPE | Filesystem type (ext4, xfs, ntfs, etc.) | | LABEL | Filesystem label | | UUID | Universally unique identifier | | MOUNTPOINT | Mount location |

Sample output: ` NAME FSTYPE LABEL UUID MOUNTPOINT sda ├─sda1 vfat 1234-5678 /boot/efi ├─sda2 ext4 abcd-efgh-ijkl-mnop /boot └─sda3 LVM2_member qrst-uvwx-yzab-cdef └─ubuntu--vg-ubuntu--lv ext4 wxyz-abcd-efgh-ijkl / `

Size and Permissions

#### Show Sizes in Bytes `bash lsblk -b ` Displays all sizes in bytes instead of human-readable format.

#### Display Permissions `bash lsblk -m ` Shows device permissions, ownership, and mode information.

Topology Information

#### Show Device Topology `bash lsblk -t ` Displays physical topology information:

| Column | Description | |--------|-------------| | ALIGNMENT | Alignment offset | | MIN-IO | Minimum I/O size | | OPT-IO | Optimal I/O size | | PHY-SEC | Physical sector size | | LOG-SEC | Logical sector size | | ROTA | Rotational device indicator | | SCHED | I/O scheduler |

Output Formats

JSON Format

`json { "blockdevices": [ { "name": "sda", "maj:min": "8:0", "rm": false, "size": "500G", "ro": false, "type": "disk", "mountpoint": null, "children": [ { "name": "sda1", "maj:min": "8:1", "rm": false, "size": "512M", "ro": false, "type": "part", "mountpoint": "/boot/efi" } ] } ] } `

Key-Value Pairs Format

` NAME="sda" MAJ:MIN="8:0" RM="0" SIZE="500G" RO="0" TYPE="disk" MOUNTPOINT="" NAME="sda1" MAJ:MIN="8:1" RM="0" SIZE="512M" RO="0" TYPE="part" MOUNTPOINT="/boot/efi" `

Raw Format

Filtering and Customization

Custom Column Selection

#### Specify Output Columns `bash lsblk -o NAME,SIZE,TYPE,MOUNTPOINT `

Available columns include:

| Column | Description | |--------|-------------| | NAME | Device name | | KNAME | Internal kernel device name | | MAJ:MIN | Major:minor device number | | FSTYPE | Filesystem type | | MOUNTPOINT | Where the device is mounted | | LABEL | Filesystem label | | UUID | Filesystem UUID | | PARTTYPE | Partition type UUID | | PARTLABEL | Partition label | | PARTUUID | Partition UUID | | RA | Read-ahead of the device | | RO | Read-only device | | RM | Removable device | | MODEL | Device identifier | | SERIAL | Disk serial number | | SIZE | Size of the device | | STATE | State of the device | | OWNER | User name | | GROUP | Group name | | MODE | Device node permissions | | ALIGNMENT | Alignment offset | | MIN-IO | Minimum I/O size | | OPT-IO | Optimal I/O size | | PHY-SEC | Physical sector size | | LOG-SEC | Logical sector size | | ROTA | Rotational device | | SCHED | I/O scheduler name | | RQ-SIZE | Request queue size | | TYPE | Device type | | DISC-ALN | Discard alignment offset | | DISC-GRAN | Discard granularity | | DISC-MAX | Discard max bytes | | DISC-ZERO | Discard zeroes data |

Filtering by Device Type

#### Show Only SCSI Devices `bash lsblk -S `

#### Show Specific Device `bash lsblk /dev/sda `

#### Multiple Devices `bash lsblk /dev/sda /dev/sdb `

Sorting Output

#### Sort by Size `bash lsblk -x SIZE `

#### Sort by Name `bash lsblk -x NAME `

Practical Use Cases

System Administration Tasks

#### Disk Space Monitoring `bash lsblk -o NAME,SIZE,AVAIL,USE%,MOUNTPOINT `

#### Finding Unmounted Devices `bash lsblk -o NAME,SIZE,TYPE,MOUNTPOINT | grep -E "(disk|part)" | grep -v "/" `

#### Checking Filesystem Types `bash lsblk -f -o NAME,FSTYPE,SIZE,MOUNTPOINT `

Storage Management

#### Before Partitioning `bash lsblk -d -o NAME,SIZE,MODEL,SERIAL `

#### After Adding New Storage `bash lsblk -f | grep -E "(disk|part)" `

#### LVM Volume Information `bash lsblk -o NAME,SIZE,TYPE | grep -E "(lvm|disk)" `

Troubleshooting Scenarios

#### Identify Boot Devices `bash lsblk -o NAME,SIZE,TYPE,MOUNTPOINT | grep -E "(/boot|/efi)" `

#### Check for Read-Only Mounts `bash lsblk -o NAME,RO,MOUNTPOINT | grep "1" `

#### Find Large Unused Devices `bash lsblk -d -o NAME,SIZE,TYPE | sort -k2 -h `

Advanced Examples

Complex Filtering and Display

#### Show Only Mounted Filesystems with Details `bash lsblk -f -o NAME,FSTYPE,SIZE,USED,AVAIL,USE%,MOUNTPOINT | grep -v "^$" | grep -E "ext4|xfs|btrfs" `

#### Display USB Devices Only `bash lsblk -o NAME,SIZE,TYPE,TRAN,MOUNTPOINT | grep usb `

#### Show Devices with Serial Numbers `bash lsblk -o NAME,SIZE,MODEL,SERIAL,TYPE -d `

Scripting Applications

#### Generate Device Inventory `bash #!/bin/bash echo "System Storage Inventory - $(date)" echo "==================================" lsblk -d -o NAME,SIZE,MODEL,SERIAL,TYPE | while read name size model serial type; do if [ "$name" != "NAME" ]; then echo "Device: $name" echo " Size: $size" echo " Model: $model" echo " Serial: $serial" echo " Type: $type" echo " Partitions:" lsblk /dev/$name -o NAME,SIZE,FSTYPE,MOUNTPOINT | tail -n +2 | sed 's/^/ /' echo "" fi done `

#### Check for Unmounted Partitions `bash #!/bin/bash unmounted=$(lsblk -rno NAME,TYPE,MOUNTPOINT | awk '$2=="part" && $3=="" {print $1}') if [ -n "$unmounted" ]; then echo "Unmounted partitions found:" for partition in $unmounted; do echo " /dev/$partition" lsblk -o NAME,SIZE,FSTYPE /dev/$partition | tail -n +2 done else echo "All partitions are mounted." fi `

Performance Analysis

#### I/O Characteristics `bash lsblk -t -o NAME,ALIGNMENT,MIN-IO,OPT-IO,PHY-SEC,LOG-SEC,ROTA,SCHED `

#### Storage Hierarchy Analysis `bash lsblk -o NAME,SIZE,TYPE,TRAN,SUBSYSTEMS | grep -E "(sata|nvme|usb|scsi)" `

Troubleshooting

Common Issues and Solutions

#### Issue: lsblk Command Not Found Problem: The system doesn't recognize the lsblk command. Solution: Install the util-linux package: `bash

Ubuntu/Debian

RHEL/CentOS/Fedora

or

#### Issue: Permission Denied Problem: Cannot access device information. Solution: Run with appropriate permissions: `bash sudo lsblk `

#### Issue: Incomplete Information Problem: Some columns show empty values. Solution: Use different options or check device status: `bash lsblk -f -a # Show all devices with filesystem info `

Verification Commands

#### Cross-Reference with Other Tools `bash

Compare with fdisk

Compare with df for mounted filesystems

Verify with /proc/partitions

Performance Considerations

The lsblk command is generally fast and lightweight, but for systems with many devices, consider:

#### Limiting Output `bash

Show only specific device types

Limit to essential columns

#### Caching Results For repeated queries in scripts: `bash

Cache output for multiple uses

Best Practices

Regular System Monitoring

1. Daily Checks: Include lsblk in daily system monitoring scripts 2. Change Detection: Compare current output with baseline to detect changes 3. Documentation: Maintain records of device configurations

Security Considerations

1. Sensitive Information: Be aware that device serial numbers and UUIDs may be sensitive 2. Access Control: Limit access to detailed device information in multi-user environments 3. Logging: Consider logging device changes for security auditing

Integration with Other Tools

The lsblk command works well with other Linux utilities:

`bash

Combine with grep for filtering

Use with awk for processing

Integrate with find for device files

This comprehensive guide covers the essential aspects of using the lsblk command effectively. The command is invaluable for understanding storage device hierarchies, managing filesystems, and troubleshooting storage-related issues in Linux systems. Regular practice with different options and scenarios will help system administrators and users become proficient in storage management tasks.