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

NAME
       btrfs-scrub - scrub btrfs filesystem, verify block checksums

SYNOPSIS
       btrfs scrub <subcommand> <args>

DESCRIPTION
       btrfs scrub is used to scrub a btrfs filesystem, which will read all data and
       metadata blocks from all devices and verify checksums. Automatically repair
       corrupted blocks if there’s a correct copy available.

           Note
           Scrub is not a filesystem checker (fsck) and does not verify nor repair
           structural damage in the filesystem. It really only checks checksums of of
           data and tree blocks, it doesn’t ensure the content of tree blocks is valid
           and consistent. There’s some validation performed when metadata blocks are
           read from disk but it’s not extensive and cannot substitute full btrfs check
           run.

       The user is supposed to run it manually or via a periodic system service. The
       recommended period is a month but could be less. The estimated device bandwidth
       utilization is about 80% on an idle filesystem. The IO priority class is by
       default idle so background scrub should not significantly interfere with normal
       filesystem operation.

       The scrubbing status is recorded in /var/lib/btrfs/ in textual files named
       scrub.status.UUID for a filesystem identified by the given UUID. (Progress state
       is communicated through a named pipe in file scrub.progress.UUID in the same
       directory.) The status file is updated every 5 seconds. A resumed scrub will
       continue from the last saved position.

SUBCOMMAND
       cancel <path>|<device>
           If a scrub is running on the filesystem identified by path cancel it.

           If a device is specified, the corresponding filesystem is found and btrfs
           scrub cancel behaves as if it was called on that filesystem.

       resume [-BdqrR] [-c <ioprio_class> -n <ioprio_classdata>] <path>|<device>
           Resume a cancelled or interrupted scrub on the filesystem identified by path
           or on a given device.

           Does not start a new scrub if the last scrub finished successfully.

           Options

           see scrub start.

       start [-BdqrRf] [-c <ioprio_class> -n <ioprio_classdata>] <path>|<device>
           Start a scrub on all devices of the filesystem identified by path or on a
           single device. If a scrub is already running, the new one fails.

           Without options, scrub is started as a background process.

           The default IO priority of scrub is the idle class. The priority can be
           configured similar to the ionice(1) syntax using -c and -n options.

           Options

           -B
               do not background and print scrub statistics when finished

           -d
               print separate statistics for each device of the filesystem (-B only) at
               the end

           -q
               be quiet, omit error messages and statistics

           -r
               run in read-only mode, do not attempt to correct anything, can be run on
               a read-only filesystem

           -R
               raw print mode, print full data instead of summary

           -c <ioprio_class>
               set IO priority class (see ionice(1) manpage)

           -n <ioprio_classdata>
               set IO priority classdata (see ionice(1) manpage)

           -f
               force starting new scrub even if a scrub is already running, this can
               useful when scrub status file is damaged and reports a running scrub
               although it is not, but should not normally be necessary

       status [-d] <path>|<device>
           Show status of a running scrub for the filesystem identified by path or for
           the specified device.

           If no scrub is running, show statistics of the last finished or cancelled
           scrub for that filesystem or device.

           Options

           -d
               print separate statistics for each device of the filesystem

EXIT STATUS
       btrfs scrub returns a zero exit status if it succeeds. Non zero is returned in
       case of failure:

       1
           scrub couldn’t be performed

       2
           there is nothing to resume

       3
           scrub found uncorrectable errors

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

SEE ALSO
       mkfs.btrfs(8), ionice(1)

Btrfs v4.20.1                          01/23/2019                        BTRFS-SCRUB(8)

usage: btrfs scrub <command> [options] <path>|<device>

    btrfs scrub start [-BdqrRf] [-c ioprio_class -n ioprio_classdata] <path>|<device>
        Start a new scrub. If a scrub is already running, the new one fails.
    btrfs scrub cancel <path>|<device>
        Cancel a running scrub
    btrfs scrub resume [-BdqrR] [-c ioprio_class -n ioprio_classdata] <path>|<device>
        Resume previously canceled or interrupted scrub
    btrfs scrub status [-dR] <path>|<device>
        Show status of running or finished scrub

verify checksums of data and metadata