1BTRFS-SCRUB(8)                   Btrfs Manual                   BTRFS-SCRUB(8)
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NAME

6       btrfs-scrub - scrub btrfs filesystem, verify block checksums
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SYNOPSIS

9       btrfs scrub <subcommand> <args>
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DESCRIPTION

12       btrfs scrub is used to scrub a btrfs filesystem, which will read all
13       data and metadata blocks from all devices and verify checksums.
14       Automatically repair corrupted blocks if there’s a correct copy
15       available.
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17           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.
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25       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.
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33       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.
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SUBCOMMAND

41       cancel <path>|<device>
42           If a scrub is running on the filesystem identified by path or
43           device, cancel it.
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45           If a device is specified, the corresponding filesystem is found and
46           btrfs scrub cancel behaves as if it was called on that filesystem.
47           The progress is saved in the status file so btrfs scrub resume can
48           continue from the last position.
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50       resume [-BdqrR] [-c <ioprio_class> -n <ioprio_classdata>]
51       <path>|<device>
52           Resume a cancelled or interrupted scrub on the filesystem
53           identified by path or on a given device. The starting point is read
54           from the status file if it exists.
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56           This does not start a new scrub if the last scrub finished
57           successfully.
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59           Options
60
61           see scrub start.
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63       start [-BdqrRf] [-c <ioprio_class> -n <ioprio_classdata>]
64       <path>|<device>
65           Start a scrub on all devices of the filesystem identified by path
66           or on a single device. If a scrub is already running, the new one
67           will not start.
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69           Without options, scrub is started as a background process. The
70           automatic repairs of damaged copies is performed by default for
71           block group profiles with redundancy.
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73           The default IO priority of scrub is the idle class. The priority
74           can be configured similar to the ionice(1) syntax using -c and -n
75           options. Note that not all IO schedulers honor the ionice settings.
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77           Options
78
79           -B
80               do not background and print scrub statistics when finished
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82           -d
83               print separate statistics for each device of the filesystem (-B
84               only) at the end
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86           -q
87               be quiet, omit error messages and statistics
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89           -r
90               run in read-only mode, do not attempt to correct anything, can
91               be run on a read-only filesystem
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93           -R
94               raw print mode, print full data instead of summary
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96           -c <ioprio_class>
97               set IO priority class (see ionice(1) manpage)
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99           -n <ioprio_classdata>
100               set IO priority classdata (see ionice(1) manpage)
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102           -f
103               force starting new scrub even if a scrub is already running,
104               this can useful when scrub status file is damaged and reports a
105               running scrub although it is not, but should not normally be
106               necessary
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108       status [-d] <path>|<device>
109           Show status of a running scrub for the filesystem identified by
110           path or for the specified device.
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112           If no scrub is running, show statistics of the last finished or
113           cancelled scrub for that filesystem or device.
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115           Options
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117           -d
118               print separate statistics for each device of the filesystem
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EXIT STATUS

121       btrfs scrub returns a zero exit status if it succeeds. Non zero is
122       returned in case of failure:
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124       1
125           scrub couldn’t be performed
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127       2
128           there is nothing to resume
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130       3
131           scrub found uncorrectable errors
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AVAILABILITY

134       btrfs is part of btrfs-progs. Please refer to the btrfs wiki
135       http://btrfs.wiki.kernel.org for further details.
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SEE ALSO

138       mkfs.btrfs(8), ionice(1)
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142Btrfs v5.6                        04/05/2020                    BTRFS-SCRUB(8)
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