Provided by: btrfs-progs_5.16.2-1_amd64 bug


       btrfs-check - check or repair a btrfs filesystem


       btrfs check [options] <device>


       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

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

           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. Eg. 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.


           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.

           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

           indicate progress at various checking phases

           verify qgroup accounting and compare against filesystem accounting

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

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

       -s|--super <superblock>
           use 'superblock’th 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.

       --clear-space-cache v1|v2
           completely wipe all free space cache of given type

           For free space cache v1, the clear_cache kernel mount option only rebuilds the free
           space cache for block groups that are modified while the filesystem is mounted with
           that option. Thus, using this option with v1 makes it possible to actually clear the
           entire free space cache.

           For free space cache v2, the clear_cache kernel mount option destroys the entire free
           space cache. This option, with v2 provides an alternative method of clearing the free
           space cache that doesn’t require mounting the filesystem.

           remove leftover items pertaining to the deprecated inode map feature


           enable the repair mode and attempt to fix problems where possible

               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

           create a new checksum tree and recalculate checksums in all files

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

           build the extent tree from scratch

               Do not use unless you know what you’re doing.

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

           The MODE can be one of:

               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

               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.

                   lowmem mode does not work with --repair yet, and is still considered

           allow work on a mounted filesystem. Note that this should work fine on a quiescent or
           read-only mounted filesystem but may crash if the device is changed externally, eg. by
           the kernel module. Repair without mount checks is not supported right now.

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


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


       btrfs is part of btrfs-progs. Please refer to the btrfs wiki
       for further details.


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