How to Use the Command 'btrfs inspect-internal' (with Examples)

The btrfs inspect-internal command is part of the Btrfs (B-tree file system) toolkit, which is utilized for querying internal information of a Btrfs filesystem. Btrfs is a modern filesystem that provides powerful data management features such as snapshotting, self-healing, and balancing. The btrfs inspect-internal command offers various subcommands to retrieve detailed information about the filesystem, such as superblock data, metadata, inode file lists, and more, enabling users and system administrators to perform diagnostic checks, data recovery, or system performance improvements.

Use case 1: Print Superblock’s Information

Code:

sudo btrfs inspect-internal dump-super path/to/partition

Motivation:
The superblock is a critical component of any filesystem, containing metadata about the entire filesystem structure. For Btrfs, examining the superblock’s information can help troubleshoot issues or verify the integrity of the filesystem. Understanding what is stored in the superblock allows administrators to access vital metadata, such as filesystem UUIDs, sizes, and versions, which is essential for recovery and repair operations.

Explanation:

• sudo: Executes the command with administrative privileges because accessing filesystem internals typically requires root access.
• btrfs inspect-internal: Specifies the command for inspecting internal structures of the Btrfs filesystem.
• dump-super: Subcommand to extract and print information contained in the superblock.
• path/to/partition: An argument specifying the path to the Btrfs partition to be examined.

Example output:

superblock 0: bytenr=65536, device=/dev/sda1
        magic:                   _BHRfS_M
        label:                   my_btrfs_volume
        uuid:                    a1234567-89ab-cdef-0123-456789abcdef
        ...

Use case 2: Print Superblock’s and All of Its Copies’ Information

Code:

sudo btrfs inspect-internal dump-super --all path/to/partition

Motivation:
Btrfs maintains multiple copies of its superblock in different locations on the disk for redundancy. Examining all copies is crucial for gaining insights into filesystem integrity and ensuring that redundant data matches. If inconsistencies are found, corrective measures can be taken to safeguard data, a vital step during recovery operations.

Explanation:

• sudo: Grants necessary permissions to access the disk directly.
• btrfs inspect-internal: Base command for internal inspection of Btrfs.
• dump-super: Targets the superblock information specifically.
• --all: Flags the command to output all existing copies of the superblock for cross-verification.
• path/to/partition: Designates the partition path for the operation.

Example output:

superblock 0: bytenr=65536, device=/dev/sda1
        ...

superblock 1: bytenr=67108864, device=/dev/sda1
        ...

superblock 2: bytenr=274877906944, device=/dev/sda1
        ...

Use case 3: Print Filesystem’s Metadata Information

Code:

sudo btrfs inspect-internal dump-tree path/to/partition

Motivation:
Analyzing the metadata structure of a Btrfs filesystem helps diagnose complex issues or understand how data is organized within B-trees. This is beneficial for developers or system administrators who need to verify the data structure integrity, debug issues related to file storage, or optimize data management strategies.

Explanation:

• sudo: Required for permissions to inspect filesystem internals.
• btrfs inspect-internal: Command for accessing Btrfs filesystem’s internal information.
• dump-tree: Subcommand to output the tree structure of metadata.
• path/to/partition: Specifies the target Btrfs partition for tree data extraction.

Example output:

inode 256 root 5 block 22528 generation 6 owner 0
    refs 1 link count 1
        ...

Use case 4: Print List of Files in Inode n-th

Code:

sudo btrfs inspect-internal inode-resolve n path/to/btrfs_mount

Motivation:
Inodes are fundamental data structures that store information about files and directories. Understanding which files correspond to a specific inode aids in debugging file system issues, recovering lost files, or tracking filesystem changes.

Explanation:

• sudo: Needed to access filesystem details securely.
• btrfs inspect-internal: Command suite for scrutinizing Btrfs internals.
• inode-resolve: Subcommand to resolve and list files associated with a specific inode number.
• n: Placeholder for the actual inode number you wish to investigate.
• path/to/btrfs_mount: Defines the specific Btrfs mount point for inode resolutions.

Example output:

123: /home/user/docs/myfile.txt

Use case 5: Print List of Files at a Given Logical Address

Code:

sudo btrfs inspect-internal logical-resolve logical_address path/to/btrfs_mount

Motivation:
Occasionally, it becomes necessary to inspect specific logical addresses on the disk for forensic analysis, recovering data, or understanding disk layout. This ability enhances control over specific disk sectors, making data tracking and file recovery more manageable.

Explanation:

• sudo: Prerequisite for executing commands involving disk sectors.
• btrfs inspect-internal: Command interface to access internal data structures.
• logical-resolve: Subcommand used to find files linked to a specified logical disk address.
• logical_address: The logical sector address on the disk you wish to inspect.
• path/to/btrfs_mount: Indicates the mount point of the Btrfs filesystem for operation context.

Example output:

1048576: /var/log/syslog

Use case 6: Print Stats of Root, Extent, Csum, and FS Trees

Code:

sudo btrfs inspect-internal tree-stats path/to/partition

Motivation:
Tracking statistics of different trees in the Btrfs filesystem, such as root, extent, csum, and filesystem (FS) trees, is vital for optimizing performance, understanding resource usage, and ensuring healthy operation of the filesystem. This detailed information assists in identifying bottlenecks or verifying the balance state of the filesystem.

Explanation:

• sudo: Mandatory for thorough filesystem inspection.
• btrfs inspect-internal: Suite for detailed Btrfs filesystem querying.
• tree-stats: Used to accumulate and present statistical data for different filesystem trees.
• path/to/partition: Lists the partition where the stats are to be calculated.

Example output:

root tree stats
    total bytes=46080, total extents=30
extent tree stats
    total bytes=32768, total extents=12
...

Conclusion:

The btrfs inspect-internal command provides essential insights into the internal workings of Btrfs filesystems. It allows users and system administrators to extract detailed information about superblocks, metadata structures, inodes, logical addresses, and statistical tree data, all of which are critical for troubleshooting, data recovery, and optimizing the performance of Btrfs filesystems. Understanding these elements can significantly contribute to maintaining a robust and efficient filesystem environment.