112 lines
3.0 KiB
Plaintext
112 lines
3.0 KiB
Plaintext
btrfs-rescue(8)
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==============
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NAME
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----
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btrfs-rescue - Recover a damaged btrfs filesystem
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SYNOPSIS
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--------
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*btrfs rescue* <subcommand> <args>
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DESCRIPTION
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-----------
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*btrfs rescue* is used to try to recover a damaged btrfs filesystem.
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SUBCOMMAND
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----------
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*chunk-recover* [options] <device>::
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Recover the chunk tree by scanning the devices
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+
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`Options`
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-y::::
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assume an answer of 'yes' to all questions.
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-v::::
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verbose mode.
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-h::::
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help.
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NOTE: Since *chunk-recover* will scan the whole device, it will be *VERY* slow
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especially executed on a large device.
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*fix-device-size* <device>::
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fix device size and super block total bytes values that are do not match
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Kernel 4.11 starts to check the device size more strictly and this might
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mismatch the stored value of total bytes. See the exact error message below.
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Newer kernel will refuse to mount the filesystem where the values do not match.
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This error is not fatal and can be fixed. This command will fix the device
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size values if possible.
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----
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BTRFS error (device sdb): super_total_bytes 92017859088384 mismatch with fs_devices total_rw_bytes 92017859094528
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----
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The mismatch may also exhibit as a kernel warning:
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----
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WARNING: CPU: 3 PID: 439 at fs/btrfs/ctree.h:1559 btrfs_update_device+0x1c5/0x1d0 [btrfs]
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----
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*super-recover* [options] <device>::
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Recover bad superblocks from good copies.
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`Options`
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-y::::
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assume an answer of 'yes' to all questions.
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-v::::
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verbose mode.
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*zero-log* <device>::
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clear the filesystem log tree
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This command will clear the filesystem log tree. This may fix a specific
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set of problem when the filesystem mount fails due to the log replay. See below
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for sample stacktraces that may show up in system log.
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The common case where this happens has been fixed a long time ago,
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so it is unlikely that you will see this particular problem, but the utility is
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kept around.
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+
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NOTE: clearing the log may lead to loss of changes that were made since the
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last transaction commit. This may be up to 30 seconds (default commit period)
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or less if the commit was implied by other filesystem activity.
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One can determine whether *zero-log* is needed according to the kernel
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backtrace:
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----
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? replay_one_dir_item+0xb5/0xb5 [btrfs]
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? walk_log_tree+0x9c/0x19d [btrfs]
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? btrfs_read_fs_root_no_radix+0x169/0x1a1 [btrfs]
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? btrfs_recover_log_trees+0x195/0x29c [btrfs]
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? replay_one_dir_item+0xb5/0xb5 [btrfs]
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? btree_read_extent_buffer_pages+0x76/0xbc [btrfs]
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? open_ctree+0xff6/0x132c [btrfs]
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----
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If the errors are like above, then *zero-log* should be used to clear
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the log and the filesystem may be mounted normally again. The keywords to look
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for are 'open_ctree' which says that it's during mount and function names
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that contain 'replay', 'recover' or 'log_tree'.
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EXIT STATUS
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-----------
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*btrfs rescue* returns a zero exit status if it succeeds. Non zero is
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returned in case of failure.
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AVAILABILITY
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------------
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*btrfs* is part of btrfs-progs.
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Please refer to the btrfs wiki http://btrfs.wiki.kernel.org for
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further details.
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SEE ALSO
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--------
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`mkfs.btrfs`(8),
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`btrfs-scrub`(8),
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`btrfs-check`(8)
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