1BTRFS-SCRUB(8) BTRFS 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 Scrub is a pass over all filesystem data and metadata and verifying the
13 checksums. If a valid copy is available (replicated block group pro‐
14 files) then the damaged one is repaired. All copies of the replicated
15 profiles are validated.
16 NOTE:
18 Scrub is not a filesystem checker (fsck) and does not verify nor re‐
19 pair 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 per‐
22 formed when metadata blocks are read from disk but it's not exten‐
23 sive and cannot substitute full btrfs check run.
24 The user is supposed to run it manually or via a periodic system ser‐
26 vice. The recommended period is a month but could be less. The esti‐
27 mated device bandwidth utilization is about 80% on an idle filesystem.
28 The IO priority class is by default idle so background scrub should not
29 significantly interfere with normal filesystem operation. The IO sched‐
30 uler set for the device(s) might not support the priority classes
31 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 po‐
38 sition.
39 Scrub can be started only on a mounted filesystem, though it's possible
41 to scrub only a selected device. See btrfs 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
49 and btrfs scrub cancel behaves as if it was called on that
50 filesystem. The progress is saved in the status file so btrfs
51 scrub resume can continue from the last position.
52 resume [-BdqrR] [-c <ioprio_class> -n <ioprio_classdata>] <path>|<de‐
54 vice>
55 Resume a cancelled or interrupted scrub on the filesystem iden‐
56 tified 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 suc‐
60 cessfully.
61 Options
63 see scrub start.
65 start [-BdqrRf] [-c <ioprio_class> -n <ioprio_classdata>] <path>|<de‐
67 vice>
68 Start a scrub on all devices of the mounted filesystem identi‐
69 fied by path or on a single device. If a scrub is already run‐
70 ning, the new one will not start. A device of an unmounted
71 filesystem cannot 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
79 -n options. Note that not all IO schedulers honor the ionice
80 settings.
81 Options
83 -B do not background and print scrub statistics when fin‐
85 ished
86 -d print separate statistics for each device of the filesys‐
88 tem (-B only) at the end
89 -r run in read-only mode, do not attempt to correct any‐
91 thing, can be run on a read-only filesystem
92 -R raw print mode, print full data instead of summary
94 -c <ioprio_class>
96 set IO priority class (see ionice(1) manpage)
97 -n <ioprio_classdata>
99 set IO priority classdata (see ionice(1) manpage)
100 -f force starting new scrub even if a scrub is already run‐
102 ning, this can useful when scrub status file is damaged
103 and reports a running scrub although it is not, but
104 should not normally be necessary
105 -q (deprecated) alias for global -q option
107 status [options] <path>|<device>
109 Show status of a running scrub for the filesystem identified by
110 path or for the specified device.
111 If no scrub is running, show statistics of the last finished or
113 cancelled scrub for that filesystem or device.
114 Options
116 -d print separate statistics for each device of the filesys‐
118 tem
119 -R print all raw statistics without postprocessing as re‐
121 turned by the status ioctl
122 --raw print all numbers raw values in bytes without the B suf‐
124 fix
125 --human-readable
127 print human friendly numbers, base 1024, this is the de‐
128 fault
129 --iec select the 1024 base for the following options, according
131 to the IEC standard
132 --si select the 1000 base for the following options, according
134 to the SI standard
135 --kbytes
137 show sizes in KiB, or kB with --si
138 --mbytes
140 show sizes in MiB, or MB with --si
141 --gbytes
143 show sizes in GiB, or GB with --si
144 --tbytes
146 show sizes in TiB, or TB with --si
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149 btrfs scrub returns a zero exit status if it succeeds. Non zero is re‐
150 turned in case of failure:
151 1 scrub couldn't be performed
153 2 there is nothing to resume
155 3 scrub found uncorrectable errors
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159 btrfs is part of btrfs-progs. Please refer to the btrfs wiki
160 http://btrfs.wiki.kernel.org for further details.
161
163 mkfs.btrfs(8), ionice(1)
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166 2022
1675.18 May 25, 2022 BTRFS-SCRUB(8)