Provided by: btrfs-progs_6.2-1_amd64 bug

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.

              -h     help.

              -v     (deprecated) alias for global -v option

       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]

       clear-uuid-tree <device>
              Clear UUID tree, so that kernel can re-generate 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.

       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 due to the log replay. See below for sample
              stack traces 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    documentation    at
       https://btrfs.readthedocs.io or wiki http://btrfs.wiki.kernel.org for further information.

SEE ALSO

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