Provided by: btrfs-tools_4.4-1_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.

       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 has been fixed a long time ago, so it is unlikely that
       you will see this particular problem, but the utility 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 log_tree.


       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)