btrfs-rescue(8) — Linux manual page

NAME \| SYNOPSIS \| DESCRIPTION \| SUBCOMMAND \| EXIT STATUS \| AVAILABILITY \| SEE ALSO \| COLOPHON

BTRFS-RESCUE(8)               Btrfs Manual               BTRFS-RESCUE(8)

NAME top

       btrfs-rescue - Recover a damaged btrfs filesystem

SYNOPSIS top

       btrfs rescue <subcommand> <args>

DESCRIPTION top

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

SUBCOMMAND top

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 top

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

AVAILABILITY top

       btrfs is part of btrfs-progs. Please refer to the btrfs wiki
       http://btrfs.wiki.kernel.org for further details.

COLOPHON top

       This page is part of the btrfs-progs (btrfs filesystem tools)
       project.  Information about the project can be found at 
       ⟨https://btrfs.wiki.kernel.org/index.php/Btrfs_source_repositories⟩.
       If you have a bug report for this manual page, see
       ⟨https://btrfs.wiki.kernel.org/index.php/Problem_FAQ#How_do_I_report_bugs_and_issues.3F⟩.
       This page was obtained from the project's upstream Git repository
       ⟨git://git.kernel.org/pub/scm/linux/kernel/git/kdave/btrfs-progs.git⟩
       on 2023-12-22.  (At that time, the date of the most recent commit
       that was found in the repository was 2023-12-14.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org

Btrfs v5.16.1                  02/06/2022                BTRFS-RESCUE(8)

Pages that refer to this page: btrfs(8), btrfs-check(8), btrfs-restore(8)