1BTRFS-RESCUE(8) BTRFS BTRFS-RESCUE(8)
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6 btrfs-rescue - recover a damaged btrfs filesystem
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9 btrfs rescue <subcommand> <args>
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12 btrfs rescue is used to try to recover a damaged btrfs filesystem.
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15 chunk-recover [options] <device>
16 Recover the chunk tree by scanning the devices
17 Options
19 -y assume an answer of yes to all questions.
21 -h help.
23 -v (deprecated) alias for global -v option
25 NOTE:
27 Since chunk-recover will scan the whole device, it will be very slow
28 especially executed on a large device.
29 fix-device-size <device>
31 fix device size and super block total bytes values that are do
32 not match
33 Kernel 4.11 starts to check the device size more strictly and
35 this might mismatch the stored value of total bytes. See the ex‐
36 act error message below. Newer kernel will refuse to mount the
37 filesystem where the values do not match. This error is not fa‐
38 tal and can be fixed. This command will fix the device size
39 values if possible.
40 BTRFS error (device sdb): super_total_bytes 92017859088384 mismatch with fs_devices total_rw_bytes 92017859094528
42 The mismatch may also exhibit as a kernel warning:
44 WARNING: CPU: 3 PID: 439 at fs/btrfs/ctree.h:1559 btrfs_update_device+0x1c5/0x1d0 [btrfs]
46 clear-uuid-tree <device>
48 Clear UUID tree, so that kernel can re-generate it at next
49 read-write mount.
50 Since kernel v4.16 there are more sanity check performed, and
52 sometimes non-critical trees like UUID tree can cause problems
53 and reject the mount. In such case, clearing UUID tree may make
54 the filesystem to be mountable again without much risk as it's
55 built from other trees.
56 super-recover [options] <device>
58 Recover bad superblocks from good copies.
59 Options
61 -y assume an answer of yes to all questions.
63 -v (deprecated) alias for global -v option
65 zero-log <device>
67 clear the filesystem log tree
68 This command will clear the filesystem log tree. This may fix a
70 specific set of problem when the filesystem mount fails due to
71 the log replay. See below for sample stack traces that may show
72 up in system log.
73 The common case where this happens was fixed a long time ago, so
75 it is unlikely that you will see this particular problem, but
76 the command is kept around.
77 NOTE:
79 Clearing the log may lead to loss of changes that were made
80 since the last transaction commit. This may be up to 30 sec‐
81 onds (default commit period) or less if the commit was im‐
82 plied by other filesystem activity.
83 One can determine whether zero-log is needed according to the
85 kernel backtrace:
86 ? replay_one_dir_item+0xb5/0xb5 [btrfs]
88 ? walk_log_tree+0x9c/0x19d [btrfs]
89 ? btrfs_read_fs_root_no_radix+0x169/0x1a1 [btrfs]
90 ? btrfs_recover_log_trees+0x195/0x29c [btrfs]
91 ? replay_one_dir_item+0xb5/0xb5 [btrfs]
92 ? btree_read_extent_buffer_pages+0x76/0xbc [btrfs]
93 ? open_ctree+0xff6/0x132c [btrfs]
94 If the errors are like above, then zero-log should be used to
96 clear the log and the filesystem may be mounted normally again.
97 The keywords to look for are 'open_ctree' which says that it's
98 during mount and function names that contain replay, recover or
99 log_tree.
100
102 btrfs rescue returns a zero exit status if it succeeds. Non zero is re‐
103 turned in case of failure.
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106 btrfs is part of btrfs-progs. Please refer to the documentation at
107 https://btrfs.readthedocs.io or wiki http://btrfs.wiki.kernel.org for
108 further information.
109
111 btrfs-check(8), btrfs-scrub(8), mkfs.btrfs(8)
1126.1.3 Jan 25, 2023 BTRFS-RESCUE(8)