btrfsck

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.

   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 cor‐
   rectly connected together.

   There are several cross checks that can detect wrong reference counts of shared extents, backreferences, missing extents of inodes, directory and inode  con‐
   nectivity 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

   -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.

   --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 filesys‐
          tem 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.

   --clear-ino-cache
          remove leftover items pertaining to the deprecated inode map feature

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.

   --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  condi‐
                 tions.  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.

          NOTE:
             lowmem mode does not work with --repair yet, and is still considered experimental.

   --force
          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, e.g. 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).

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 or wiki http://btrfs.wiki.kernel.org for further informa‐
   tion.