BTRFS-RESCUE(8) Btrfs Manual 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 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
(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), btrfs-scrub(8), btrfs-check(8)
Btrfs v5.7 07/02/2020 BTRFS-RESCUE(8)