Provided by: btrfs-progs_6.2-1_amd64 bug

NAME

       btrfs-scrub - scrub btrfs filesystem, verify block checksums

SYNOPSIS

       btrfs scrub <subcommand> <args>

DESCRIPTION

       Scrub  is  a  pass over all filesystem data and metadata and verifying the checksums. If a
       valid copy is available  (replicated  block  group  profiles)  then  the  damaged  one  is
       repaired. All copies of the replicated profiles are validated.

       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.

       Scrub  can  be  started only on a mounted filesystem, though it's possible to scrub only a
       selected device. See btrfs scrub start for more.

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 mounted filesystem identified by path or on a
              single device. If a scrub is already running, the new one will not start. A  device
              of an unmounted filesystem cannot be scrubbed this way.

              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 [options] <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

              -R     print all raw statistics without postprocessing as returned  by  the  status
                     ioctl

              --raw  print all numbers raw values in bytes without the B suffix

              --human-readable
                     print human friendly numbers, base 1024, this is the default

              --iec  select  the  1024  base  for  the  following  options,  according to the IEC
                     standard

              --si   select the 1000 base for the following options, according to the SI standard

              --kbytes
                     show sizes in KiB, or kB with --si

              --mbytes
                     show sizes in MiB, or MB with --si

              --gbytes
                     show sizes in GiB, or GB with --si

              --tbytes
                     show sizes in TiB, or TB with --si

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   documentation   at
       https://btrfs.readthedocs.io or wiki http://btrfs.wiki.kernel.org for further information.

SEE ALSO

       mkfs.btrfs(8), ionice(1)