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)