1BTRFS-RESCUE(8)                  Btrfs Manual                  BTRFS-RESCUE(8)
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NAME

6       btrfs-rescue - Recover a damaged btrfs filesystem
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SYNOPSIS

9       btrfs rescue <subcommand> <args>
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DESCRIPTION

12       btrfs rescue is used to try to recover a damaged btrfs filesystem.
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SUBCOMMAND

15       chunk-recover [options] <device>
16           Recover the chunk tree by scanning the devices
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18           Options
19
20           -y
21               assume an answer of yes to all questions.
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23           -v
24               verbose mode.
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26           -h
27               help.
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29           Note
30           Since chunk-recover will scan the whole device, it will be VERY
31           slow especially executed on a large device.
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33       fix-device-size <device>
34           fix device size and super block total bytes values that are do not
35           match
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37           Kernel 4.11 starts to check the device size more strictly and this
38           might mismatch the stored value of total bytes. See the exact error
39           message below. Newer kernel will refuse to mount the filesystem
40           where the values do not match. This error is not fatal and can be
41           fixed. This command will fix the device size values if possible.
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43               BTRFS error (device sdb): super_total_bytes 92017859088384 mismatch with fs_devices total_rw_bytes 92017859094528
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45           The mismatch may also exhibit as a kernel warning:
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47               WARNING: CPU: 3 PID: 439 at fs/btrfs/ctree.h:1559 btrfs_update_device+0x1c5/0x1d0 [btrfs]
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49       super-recover [options] <device>
50           Recover bad superblocks from good copies.
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52           Options
53
54           -y
55               assume an answer of yes to all questions.
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57           -v
58               verbose mode.
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60       zero-log <device>
61           clear the filesystem log tree
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63           This command will clear the filesystem log tree. This may fix a
64           specific set of problem when the filesystem mount fails due to the
65           log replay. See below for sample stacktraces that may show up in
66           system log.
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68           The common case where this happens was fixed a long time ago, so it
69           is unlikely that you will see this particular problem, but the
70           command is kept around.
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72               Note
73               clearing the log may lead to loss of changes that were made
74               since the last transaction commit. This may be up to 30 seconds
75               (default commit period) or less if the commit was implied by
76               other filesystem activity.
77           One can determine whether zero-log is needed according to the
78           kernel backtrace:
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80               ? replay_one_dir_item+0xb5/0xb5 [btrfs]
81               ? walk_log_tree+0x9c/0x19d [btrfs]
82               ? btrfs_read_fs_root_no_radix+0x169/0x1a1 [btrfs]
83               ? btrfs_recover_log_trees+0x195/0x29c [btrfs]
84               ? replay_one_dir_item+0xb5/0xb5 [btrfs]
85               ? btree_read_extent_buffer_pages+0x76/0xbc [btrfs]
86               ? open_ctree+0xff6/0x132c [btrfs]
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88           If the errors are like above, then zero-log should be used to clear
89           the log and the filesystem may be mounted normally again. The
90           keywords to look for are open_ctree which says that it’s during
91           mount and function names that contain replay, recover or log_tree.
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EXIT STATUS

94       btrfs rescue returns a zero exit status if it succeeds. Non zero is
95       returned in case of failure.
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AVAILABILITY

98       btrfs is part of btrfs-progs. Please refer to the btrfs wiki
99       http://btrfs.wiki.kernel.org for further details.
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SEE ALSO

102       mkfs.btrfs(8), btrfs-scrub(8), btrfs-check(8)
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106Btrfs v5.6                        04/05/2020                   BTRFS-RESCUE(8)
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