# BTRFS-RESCUE(8) - man - phpMan

[BTRFS-RESCUE(8)](https://www.chedong.com/phpMan.php/man/BTRFS-RESCUE/8/markdown)                             Btrfs Manual                             [BTRFS-RESCUE(8)](https://www.chedong.com/phpMan.php/man/BTRFS-RESCUE/8/markdown)



## 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 and 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 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)](https://www.chedong.com/phpMan.php/man/mkfs.btrfs/8/markdown), [**btrfs-scrub**(8)](https://www.chedong.com/phpMan.php/man/btrfs-scrub/8/markdown), [**btrfs-check**(8)](https://www.chedong.com/phpMan.php/man/btrfs-check/8/markdown)



Btrfs v5.16.2                                02/16/2022                              [BTRFS-RESCUE(8)](https://www.chedong.com/phpMan.php/man/BTRFS-RESCUE/8/markdown)