1BTRFS-SCRUB(8) Btrfs Manual BTRFS-SCRUB(8)
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6 btrfs-scrub - scrub btrfs filesystem, verify block checksums
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9 btrfs scrub <subcommand> <args>
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12 btrfs scrub is used to scrub a mounted btrfs filesystem, which will
13 read all data and metadata blocks from all devices and verify
14 checksums. Automatically repair corrupted blocks if there’s a correct
15 copy available.
16 Note
18 Scrub is not a filesystem checker (fsck) and does not verify nor
19 repair structural damage in the filesystem. It really only checks
20 checksums of data and tree blocks, it doesn’t ensure the content of
21 tree blocks is valid and consistent. There’s some validation
22 performed when metadata blocks are read from disk but it’s not
23 extensive and cannot substitute full btrfs check run.
24 The user is supposed to run it manually or via a periodic system
26 service. The recommended period is a month but could be less. The
27 estimated device bandwidth utilization is about 80% on an idle
28 filesystem. The IO priority class is by default idle so background
29 scrub should not significantly interfere with normal filesystem
30 operation. The IO scheduler set for the device(s) might not support the
31 priority classes though.
32 The scrubbing status is recorded in /var/lib/btrfs/ in textual files
34 named scrub.status.UUID for a filesystem identified by the given UUID.
35 (Progress state is communicated through a named pipe in file
36 scrub.progress.UUID in the same directory.) The status file is updated
37 every 5 seconds. A resumed scrub will continue from the last saved
38 position.
39 Scrub can be started only on a mounted filesystem, though it’s possible
41 to scrub only a selected device. See scrub start for more.
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44 cancel <path>|<device>
45 If a scrub is running on the filesystem identified by path or
46 device, cancel it.
47 If a device is specified, the corresponding filesystem is found and
49 btrfs scrub cancel behaves as if it was called on that filesystem.
50 The progress is saved in the status file so btrfs scrub resume can
51 continue from the last position.
52 resume [-BdqrR] [-c <ioprio_class> -n <ioprio_classdata>]
54 <path>|<device>
55 Resume a cancelled or interrupted scrub on the filesystem
56 identified by path or on a given device. The starting point is read
57 from the status file if it exists.
58 This does not start a new scrub if the last scrub finished
60 successfully.
61 Options
63 see scrub start.
65 start [-BdqrRf] [-c <ioprio_class> -n <ioprio_classdata>]
67 <path>|<device>
68 Start a scrub on all devices of the mounted filesystem identified
69 by path or on a single device. If a scrub is already running, the
70 new one will not start. A device of an unmounted filesystem cannot
71 be scrubbed this way.
72 Without options, scrub is started as a background process. The
74 automatic repairs of damaged copies is performed by default for
75 block group profiles with redundancy.
76 The default IO priority of scrub is the idle class. The priority
78 can be configured similar to the ionice(1) syntax using -c and -n
79 options. Note that not all IO schedulers honor the ionice settings.
80 Options
82 -B
84 do not background and print scrub statistics when finished
85 -d
87 print separate statistics for each device of the filesystem (-B
88 only) at the end
89 -r
91 run in read-only mode, do not attempt to correct anything, can
92 be run on a read-only filesystem
93 -R
95 raw print mode, print full data instead of summary
96 -c <ioprio_class>
98 set IO priority class (see ionice(1) manpage)
99 -n <ioprio_classdata>
101 set IO priority classdata (see ionice(1) manpage)
102 -f
104 force starting new scrub even if a scrub is already running,
105 this can useful when scrub status file is damaged and reports a
106 running scrub although it is not, but should not normally be
107 necessary
108 -q
110 (deprecated) alias for global -q option
111 status [options] <path>|<device>
113 Show status of a running scrub for the filesystem identified by
114 path or for the specified device.
115 If no scrub is running, show statistics of the last finished or
117 cancelled scrub for that filesystem or device.
118 Options
120 -d
122 print separate statistics for each device of the filesystem
123 -R
125 print all raw statistics without postprocessing as returned by
126 the status ioctl
127 --raw
129 print all numbers raw values in bytes without the B suffix
130 --human-readable
132 print human friendly numbers, base 1024, this is the default
133 --iec
135 select the 1024 base for the following options, according to
136 the IEC standard
137 --si
139 select the 1000 base for the following options, according to
140 the SI standard
141 --kbytes
143 show sizes in KiB, or kB with --si
144 --mbytes
146 show sizes in MiB, or MB with --si
147 --gbytes
149 show sizes in GiB, or GB with --si
150 --tbytes
152 show sizes in TiB, or TB with --si
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155 btrfs scrub returns a zero exit status if it succeeds. Non zero is
156 returned in case of failure:
157 1
159 scrub couldn’t be performed
160 2
162 there is nothing to resume
163 3
165 scrub found uncorrectable errors
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168 btrfs is part of btrfs-progs. Please refer to the btrfs wiki
169 http://btrfs.wiki.kernel.org for further details.
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172 mkfs.btrfs(8), ionice(1)
173Btrfs v5.12.1 05/13/2021 BTRFS-SCRUB(8)