Provided by: btrfs-progs_5.2.1-1ubuntu1_amd64 bug


       btrfs-scrub - scrub btrfs filesystem, verify block checksums


       btrfs scrub <subcommand> <args>


       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.

           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 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


       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.


           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.


               do not background and print scrub statistics when finished

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

               be quiet, omit error messages and statistics

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

               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)

               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.


               print separate statistics for each device of the filesystem


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

           scrub couldn’t be performed

           there is nothing to resume

           scrub found uncorrectable errors


       btrfs is part of btrfs-progs. Please refer to the btrfs wiki
       for further details.


       mkfs.btrfs(8), ionice(1)