BTRFS-CHECK(8)			     BTRFS			BTRFS-CHECK(8)

NAME
       btrfs-check - check or repair a btrfs filesystem

SYNOPSIS
       btrfs check [options] <device>

DESCRIPTION
       The filesystem checker is used to verify structural integrity of a
       filesystem and attempt to repair it if requested.  It is recommended to
       unmount the filesystem prior to running the check, but it is possible
       to start checking a mounted filesystem (see --force).

       By default, btrfs check will not modify the device but you can reaffirm
       that by the option --readonly.

       btrfsck is an alias of btrfs check command and is now deprecated.

       NOTE:
	  Even though the filesystem checker requires a device argument, it
	  scans for all devices belonging to the same filesystem, thus it
	  should not cause a difference using different devices of the same
	  filesystem.  Furthermore btrfs-check(8) will automatically choose
	  the good mirror, thus as long as there is a good copy for metadata,
	  it will not report such case as an error.

       WARNING:
	  Do not use --repair unless you are advised to do so by a developer
	  or an experienced user, and then only after having accepted that no
	  fsck successfully repair all types of filesystem corruption. E.g.
	  some other software or hardware bugs can fatally damage a volume.

       The structural integrity check verifies if internal filesystem objects
       or data structures satisfy the constraints, point to the right objects
       or are correctly connected together.

       There are several cross checks that can detect wrong reference counts
       of shared extents, backreferences, missing extents of inodes, directory
       and inode connectivity etc.

       The amount of memory required can be high, depending on the size of the
       filesystem, similarly the run time. Check the modes that can also
       affect that.

SAFE OR ADVISORY OPTIONS

       -b|--backup
	      use the first valid set of backup roots stored in the superblock

	      This can be combined with --super if some of the superblocks are
	      damaged.

       --check-data-csum
	      verify checksums of data blocks

	      This expects that the filesystem is otherwise OK, and is
	      basically an offline scrub that does not repair data from spare
	      copies.

       --chunk-root <bytenr>
	      use the given offset bytenr for the chunk tree root

       -E|--subvol-extents <subvolid>
	      show extent state for the given subvolume

       --mode <MODE>
	      select mode of operation regarding memory and IO

	      The MODE can be one of:

	      original
		     The metadata are read into memory and verified, thus the
		     requirements are high on large filesystems and can even
		     lead to out-of-memory conditions.	The possible
		     workaround is to export the block device over network to
		     a machine with enough memory.

	      lowmem This mode is supposed to address the high memory
		     consumption at the cost of increased IO when it needs to
		     re-read blocks.  This may increase run time.

       -p|--progress
	      indicate progress at various checking phases

       -Q|--qgroup-report
	      verify qgroup accounting and compare against filesystem
	      accounting

       -r|--tree-root <bytenr>
	      use the given offset 'bytenr' for the tree root

       --readonly
	      (default) run in read-only mode, this option exists to calm
	      potential panic when users are going to run the checker

       -s|--super <N>
	      use Nth superblock copy, valid values are 0, 1 or 2 if the
	      respective superblock offset is within the device size

	      This can be used to use a different starting point if some of
	      the primary superblock is damaged.

DANGEROUS OPTIONS

       --repair
	      enable the repair mode and attempt to fix problems where
	      possible

	      NOTE:
		 There's a warning and 10 second delay when this option is run
		 without --force to give users a chance to think twice before
		 running repair, the warnings in documentation have shown to
		 be insufficient.

       --init-csum-tree
	      create a new checksum tree and recalculate checksums in all
	      files

	      WARNING:
		 Do not blindly use this option to fix checksum mismatch
		 problems.

       --init-extent-tree
	      build the extent tree from scratch

	      WARNING:
		 Do not use unless you know what you're doing.

       --force
	      allow work on a mounted filesystem and skip mount checks. Note
	      that this should work fine on a quiescent or read-only mounted
	      filesystem but may crash if the device is changed externally,
	      e.g. by the kernel module.

	      NOTE:
		 It is possible to run with --repair but on a mounted
		 filesystem that will most likely lead to a corruption unless
		 the filesystem is in a quiescent state which may not be
		 possible to guarantee.

	      This option also skips the delay and warning in the repair mode
	      (see --repair).

DEPRECATED OR REMOVED OPTIONS

       --clear-space-cache v1|v2
	      completely remove the free space cache of the given version

	      See also the clear_cache mount option.

	      WARNING:
		 This option is deprecated, please use btrfs rescue
		 clear-space-cache instead, this option would be removed in
		 the future eventually.

EXIT STATUS
       btrfs check returns a zero exit status if it succeeds. Non zero is
       returned in case of failure.

AVAILABILITY
       btrfs is part of btrfs-progs.  Please refer to the documentation at
       https://btrfs.readthedocs.io.

SEE ALSO
       mkfs.btrfs(8), btrfs-scrub(8), btrfs-rescue(8)

6.16.1			      September 10, 2025		BTRFS-CHECK(8)