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.
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 has been fixed a long time ago, so
it is unlikely that you will see this particular problem, but the
utility 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)
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