BTRFS-RESCUE(8) BTRFS BTRFS-RESCUE(8)
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 ex-
act error message below. Newer kernel will refuse to mount the
filesystem where the values do not match. This error is not fa-
tal 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 are 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 stack traces 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 sec-
onds (default commit period) or less if the commit was im-
plied 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 re-
turned in case of failure.
AVAILABILITY
btrfs is part of btrfs-progs. Please refer to the documentation at
https://btrfs.readthedocs.io or wiki http://btrfs.wiki.kernel.org for
further information.
SEE ALSO
btrfs-check(8), btrfs-scrub(8), mkfs.btrfs(8)
6.2 Oct 16, 2024 BTRFS-RESCUE(8)
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