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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 v5.4.1                      01/09/2020                   BTRFS-RESCUE(8)
NAME | SYNOPSIS | DESCRIPTION | SUBCOMMAND | EXIT STATUS | AVAILABILITY | SEE ALSO