1BTRFS-CHECK(8) Btrfs Manual 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. Eg.
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
38 affect that.
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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 basically
51 and offline scrub but does not repair data from spare copies.
52 --chunk-root <bytenr>
54 use the given offset bytenr for the chunk tree root
55 -E|--subvol-extents <subvolid>
57 show extent state for the given subvolume
58 -p|--progress
60 indicate progress at various checking phases
61 -Q|--qgroup-report
63 verify qgroup accounting and compare against filesystem accounting
64 -r|--tree-root <bytenr>
66 use the given offset bytenr for the tree root
67 --readonly
69 (default) run in read-only mode, this option exists to calm
70 potential panic when users are going to run the checker
71 -s|--super <superblock>
73 use 'superblock’th superblock copy, valid values are 0, 1 or 2 if
74 the respective superblock offset is within the device size
75 This can be used to use a different starting point if some of the
77 primary superblock is damaged.
78 --clear-space-cache v1|v2
80 completely wipe all free space cache of given type
81 For free space cache v1, the clear_cache kernel mount option only
83 rebuilds the free space cache for block groups that are modified
84 while the filesystem is mounted with that option. Thus, using this
85 option with v1 makes it possible to actually clear the entire free
86 space cache.
87 For free space cache v2, the clear_cache kernel mount option
89 destroys the entire free space cache. This option, with v2 provides
90 an alternative method of clearing the free space cache that doesn’t
91 require mounting the filesystem.
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94 --repair
95 enable the repair mode and attempt to fix problems where possible
96 Note
98 there’s a warning and 10 second delay when this option is run
99 without --force to give users a chance to think twice before
100 running repair, the warnings in documentation have shown to be
101 insufficient
102 --init-csum-tree
104 create a new checksum tree and recalculate checksums in all files
105 Note
107 Do not blindly use this option to fix checksum mismatch
108 problems.
109 --init-extent-tree
111 build the extent tree from scratch
112 Note
114 Do not use unless you know what you’re doing.
115 --mode <MODE>
117 select mode of operation regarding memory and IO
118 The MODE can be one of:
120 original
122 The metadata are read into memory and verified, thus the
123 requirements are high on large filesystems and can even lead to
124 out-of-memory conditions. The possible workaround is to export
125 the block device over network to a machine with enough memory.
126 lowmem
128 This mode is supposed to address the high memory consumption at
129 the cost of increased IO when it needs to re-read blocks. This
130 may increase run time.
131 Note
133 lowmem mode does not work with --repair yet, and is still
134 considered experimental.
135 --force
137 allow work on a mounted filesystem. Note that this should work fine
138 on a quiescent or read-only mounted filesystem but may crash if the
139 device is changed externally, eg. by the kernel module. Repair
140 without mount checks is not supported right now.
141 This option also skips the delay and warning in the repair mode
143 (see --repair).
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146 btrfs check returns a zero exit status if it succeeds. Non zero is
147 returned in case of failure.
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150 btrfs is part of btrfs-progs. Please refer to the btrfs wiki
151 http://btrfs.wiki.kernel.org for further details.
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154 mkfs.btrfs(8), btrfs-scrub(8), btrfs-rescue(8)
155Btrfs v5.4 12/03/2019 BTRFS-CHECK(8)