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

NAME
       btrfs-rescue - Recover a damaged btrfs filesystem

SYNOPSIS
       btrfs rescue <subcommand> <args>

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

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

           Options

           -y
               assume an answer of yes to all questions.

           -v
               verbose mode.

           -h
               help.

           Note
           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
           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]

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

           Options

           -y
               assume an answer of yes to all questions.

           -v
               verbose mode.

       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.

               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 btrfs wiki
       http://btrfs.wiki.kernel.org for further details.

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

Btrfs v4.20.1                            01/23/2019                          BTRFS-RESCUE(8)

usage: btrfs rescue <command> [options] <path>

    btrfs rescue chunk-recover [options] <device>
        Recover the chunk tree by scanning the devices one by one.
    btrfs rescue super-recover [options] <device>
        Recover bad superblocks from good copies
    btrfs rescue zero-log <device>
        Clear the tree log. Usable if it's corrupted and prevents mount.
    btrfs rescue fix-device-size <device>
        Re-align device and super block sizes. Usable if newer kernel refuse to mount it due to mismatch super size

toolbox for specific rescue operations