1BTRFS-CHECK(8) BTRFS BTRFS-CHECK(8)
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6 btrfs-check - check or repair a btrfs filesystem
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9 btrfs check [options] <device>
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12 The filesystem checker is used to verify structural integrity of a
13 filesystem and attempt to repair it if requested. It is recommended to
14 unmount the filesystem prior to running the check, but it is possible
15 to start checking a mounted filesystem (see --force).
16 By default, btrfs check will not modify the device but you can reaffirm
18 that by the option --readonly.
19 btrfsck is an alias of btrfs check command and is now deprecated.
21 WARNING:
23 Do not use --repair unless you are advised to do so by a developer
24 or an experienced user, and then only after having accepted that no
25 fsck successfully repair all types of filesystem corruption. E.g.
26 some other software or hardware bugs can fatally damage a volume.
27 The structural integrity check verifies if internal filesystem objects
29 or data structures satisfy the constraints, point to the right objects
30 or are correctly connected together.
31 There are several cross checks that can detect wrong reference counts
33 of shared extents, backreferences, missing extents of inodes, directory
34 and inode connectivity etc.
35 The amount of memory required can be high, depending on the size of the
37 filesystem, similarly the run time. Check the modes that can also af‐
38 fect that.
39
41 -b|--backup
42 use the first valid set of backup roots stored in the superblock
43 This can be combined with --super if some of the superblocks are
45 damaged.
46 --check-data-csum
48 verify checksums of data blocks
49 This expects that the filesystem is otherwise OK, and is basi‐
51 cally an offline scrub that does not repair data from spare
52 copies.
53 --chunk-root <bytenr>
55 use the given offset bytenr for the chunk tree root
56 -E|--subvol-extents <subvolid>
58 show extent state for the given subvolume
59 -p|--progress
61 indicate progress at various checking phases
62 -Q|--qgroup-report
64 verify qgroup accounting and compare against filesystem account‐
65 ing
66 -r|--tree-root <bytenr>
68 use the given offset 'bytenr' for the tree root
69 --readonly
71 (default) run in read-only mode, this option exists to calm po‐
72 tential panic when users are going to run the checker
73 -s|--super <N>
75 use Nth superblock copy, valid values are 0, 1 or 2 if the re‐
76 spective superblock offset is within the device size
77 This can be used to use a different starting point if some of
79 the primary superblock is damaged.
80 --clear-space-cache v1|v2
82 completely remove the free space cache of the given version
83 See also the clear_cache mount option.
85 WARNING:
87 This option is deprecated, please use btrfs rescue
88 clear-space-cache instead, this option would be removed in
89 the future eventually.
90 --clear-ino-cache
92 remove leftover items pertaining to the deprecated inode cache
93 feature
94 WARNING:
96 This option is deprecated, please use btrfs rescue
97 clear-ino-cache instead, this option would be removed in the
98 future eventually.
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101 --repair
102 enable the repair mode and attempt to fix problems where possi‐
103 ble
104 NOTE:
106 There's a warning and 10 second delay when this option is run
107 without --force to give users a chance to think twice before
108 running repair, the warnings in documentation have shown to
109 be insufficient.
110 --init-csum-tree
112 create a new checksum tree and recalculate checksums in all
113 files
114 WARNING:
116 Do not blindly use this option to fix checksum mismatch prob‐
117 lems.
118 --init-extent-tree
120 build the extent tree from scratch
121 WARNING:
123 Do not use unless you know what you're doing.
124 --mode <MODE>
126 select mode of operation regarding memory and IO
127 The MODE can be one of:
129 original
131 The metadata are read into memory and verified, thus the
132 requirements are high on large filesystems and can even
133 lead to out-of-memory conditions. The possible work‐
134 around is to export the block device over network to a
135 machine with enough memory.
136 lowmem This mode is supposed to address the high memory consump‐
138 tion at the cost of increased IO when it needs to re-read
139 blocks. This may increase run time.
140 NOTE:
142 lowmem mode does not work with --repair yet, and is still
143 considered experimental.
144 --force
146 allow work on a mounted filesystem and skip mount checks. Note
147 that this should work fine on a quiescent or read-only mounted
148 filesystem but may crash if the device is changed externally,
149 e.g. by the kernel module.
150 NOTE:
152 It is possible to run with --repair but on a mounted filesys‐
153 tem that will most likely lead to a corruption unless the
154 filesystem is in a quiescent state which may not be possible
155 to guarantee.
156 This option also skips the delay and warning in the repair mode
158 (see --repair).
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161 btrfs check returns a zero exit status if it succeeds. Non zero is re‐
162 turned in case of failure.
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165 btrfs is part of btrfs-progs. Please refer to the documentation at
166 https://btrfs.readthedocs.io.
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169 mkfs.btrfs(8), btrfs-scrub(8), btrfs-rescue(8)
1706.6.2 Nov 24, 2023 BTRFS-CHECK(8)