Provided by: btrfs-progs_5.2.1-1ubuntu1_amd64 bug


       btrfs-rescue - Recover a damaged btrfs filesystem


       btrfs rescue <subcommand> <args>


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


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


               assume an answer of yes to all questions.

               verbose mode.


           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.


               assume an answer of yes to all questions.

               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.

               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


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


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


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