BTRFS-RESCUE(8)			     BTRFS		       BTRFS-RESCUE(8)

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)

6.16.1			      September 10, 2025	       BTRFS-RESCUE(8)