BTRFS-SCRUB(8)

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 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 IO scheduler set for the device(s) might not support the
       priority classes though.

       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 or
           device, 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.
           The progress is saved in the status file so btrfs scrub resume can
           continue from the last position.

       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. The starting point is read
           from the status file if it exists.

           This 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
           will not start.

           Without options, scrub is started as a background process. The
           automatic repairs of damaged copies is performed by default for
           block group profiles with redundancy.

           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. Note that not all IO schedulers honor the ionice settings.

           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

           -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

           -q
               (deprecated) alias for global -q option

       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 v5.7                        07/02/2020                    BTRFS-SCRUB(8)