btrfs-rescue(8) — Linux manual page


BTRFS-RESCUE(8)                 Btrfs Manual                 BTRFS-RESCUE(8)

NAME         top

       btrfs-rescue - Recover a damaged btrfs filesystem

SYNOPSIS         top

       btrfs rescue <subcommand> <args>

DESCRIPTION         top

       btrfs rescue is used to try to recover a damaged btrfs filesystem.

SUBCOMMAND         top

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


               assume an answer of yes to all questions.


               (deprecated) alias for global -v option

           Since chunk-recover will scan the whole device, it will be VERY
           slow especially executed on a large device.

       fix-device-size <device>
           fix device size and super block total bytes values that are 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

               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]

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


               assume an answer of yes to all questions.

               (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 due to
           the log replay. See below for sample stacktraces that may show up
           in system log.

           The common case where this happens was fixed a long time ago, so
           it is unlikely that you will see this particular problem, but the
           command is kept around.

               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

EXIT STATUS         top

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

AVAILABILITY         top

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

SEE ALSO         top

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

COLOPHON         top

       This page is part of the btrfs-progs (btrfs filesystem tools)
       project.  Information about the project can be found at 
       If you have a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       on 2020-09-18.  (At that time, the date of the most recent commit
       that was found in the repository was 2020-07-02.)  If you discover
       any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page, or
       you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a mail

Btrfs v4.6.1                     07/14/2020                  BTRFS-RESCUE(8)

Pages that refer to this page: btrfs(8)btrfs-check(8)btrfsck(8)btrfs-restore(8)