NAME

       btrfs-rescue - recover a damaged btrfs filesystem

SYNOPSIS

       btrfs rescue <subcommand> <args>

DESCRIPTION

       A   set   of  commands  that  are  targeting  to  fix  a  specific  problem  and  may  not  suitable  for
       :doc`btrfs-check`.

SUBCOMMAND

       chunk-recover [options] <device>
              Recover the chunk tree by scanning the devices

              Options

              -y     assume an answer of yes to all questions.

              -h     help.

              -v     (deprecated) alias for global -v option

       NOTE:
          Since chunk-recover will scan the whole device, it will be very slow especially if executed on a large
          device.

       fix-device-size <device>
              Fix device size and super block total bytes values that do not match.

              Kernel 4.11 starts to check the device size more strictly and this might mismatch the stored value
              of total bytes. See the exact error  message  below.   Newer  kernel  will  refuse  to  mount  the
              filesystem where the values do not match.  This error is not fatal and can be fixed.  This command
              will fix the device size values if possible.

                 BTRFS error (device sdb): super_total_bytes 92017859088384 mismatch with fs_devices total_rw_bytes 92017859094528

              The mismatch may also exhibit as a kernel warning:

                 WARNING: CPU: 3 PID: 439 at fs/btrfs/ctree.h:1559 btrfs_update_device+0x1c5/0x1d0 [btrfs]

       fix-data-checksum <device>
              Selectively fix data checksum mismatch.

              There  is a long existing problem that if a user space program is doing direct IO and modifies the
              buffer before the write back finished, it can lead to data checksum mismatches.

              This problem is known but not fixed until upstream release v6.15 (backported to older kernels). So
              it's possible to hit false data checksum mismatch for any long running btrfs.

              In that case this program can be utilized to repair such problem.

              Options

              -r|--readonly
                     readonly mode, only scan for and report data checksum mismatches, do not repair

              -i|--interactive
                     interactive mode, ask for how to repair, ignore the errors by default

              -m|--mirror <num>
                     use specified mirror to update the checksum item for all corrupted blocks.

                     The value must be >= 1, and if the corrupted block has fewer mirrors than  the  value,  the
                     mirror number will be num % (num_mirrors + 1).

       clear-ino-cache <device>
              Remove leftover items pertaining to the deprecated inode number cache feature.

              The feature enabled by mount option inode_cache has been completely removed in 5.11 kernel.

       clear-space-cache <v1|v2> <device>
              Completely remove the on-disk data of free space cache of given version.

              Especially  for  v1  free  space  cache,  clear_cache mount option would only remove the cache for
              updated block groups, the remaining would not be  removed.   Thus  this  command  is  provided  to
              manually clear the free space cache.

       clear-uuid-tree <device>
              Clear the UUID tree, so that kernel can regenerate it at next read-write mount.

              Since  kernel  v4.16  there are more sanity check performed, and sometimes non-critical trees like
              UUID tree can cause problems and reject the mount.  In such case, clearing UUID tree may make  the
              filesystem to be mountable again without much risk as it's built from other trees.  See also mount
              option rescan_uuid_tree (in btrfs-man5).

       super-recover [options] <device>
              Recover bad superblocks from good copies.

              Options

              -y     assume an answer of yes to all questions.

              -v     (deprecated) alias for global -v option

       zero-log <device>
              Clear the filesystem log tree.

              This  command  will clear the filesystem log tree. This may fix a specific set of problem when the
              filesystem mount fails during log replay. See below for sample stack traces that may  show  up  in
              system log.

              NOTE:
                 Clearing  the log may lead to loss of changes that were made since the last transaction commit.
                 This may be up to 30 seconds (default commit period) or less if the commit was implied by other
                 filesystem activity.

              One can determine whether zero-log is needed according to the kernel backtrace:

                 ? replay_one_dir_item+0xb5/0xb5 [btrfs]
                 ? walk_log_tree+0x9c/0x19d [btrfs]
                 ? btrfs_read_fs_root_no_radix+0x169/0x1a1 [btrfs]
                 ? btrfs_recover_log_trees+0x195/0x29c [btrfs]
                 ? replay_one_dir_item+0xb5/0xb5 [btrfs]
                 ? btree_read_extent_buffer_pages+0x76/0xbc [btrfs]
                 ? open_ctree+0xff6/0x132c [btrfs]

              If the errors are like above, then zero-log should be used to clear the log and the filesystem may
              be mounted normally again. The keywords to look for are 'open_ctree' which says that  it's  during
              mount and function names that contain replay, recover or log_tree.

EXIT STATUS

       btrfs rescue 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

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

6.16                                              Sep 07, 2025                                   BTRFS-RESCUE(8)