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.

AVAILABILITY

btrfs is part of btrfs-progs. Please refer to the btrfs wiki m[blue]http://btrfs.wiki.kernel.orgm[] for further details.