158 lines
5.7 KiB
ReStructuredText
158 lines
5.7 KiB
ReStructuredText
btrfs-scrub(8)
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==============
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SYNOPSIS
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--------
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**btrfs scrub** <subcommand> <args>
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DESCRIPTION
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-----------
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**btrfs scrub** is used to scrub a mounted btrfs filesystem, which will read all
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data and metadata blocks from all devices and verify checksums. Automatically
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repair corrupted blocks if there's a correct copy available.
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.. note::
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Scrub is not a filesystem checker (fsck) and does not verify nor repair
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structural damage in the filesystem. It really only checks checksums of data
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and tree blocks, it doesn't ensure the content of tree blocks is valid and
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consistent. There's some validation performed when metadata blocks are read
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from disk but it's not extensive and cannot substitute full *btrfs check*
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run.
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The user is supposed to run it manually or via a periodic system service. The
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recommended period is a month but could be less. The estimated device bandwidth
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utilization is about 80% on an idle filesystem. The IO priority class is by
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default *idle* so background scrub should not significantly interfere with
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normal filesystem operation. The IO scheduler set for the device(s) might not
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support the priority classes though.
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The scrubbing status is recorded in */var/lib/btrfs/* in textual files named
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*scrub.status.UUID* for a filesystem identified by the given UUID. (Progress
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state is communicated through a named pipe in file *scrub.progress.UUID* in the
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same directory.) The status file is updated every 5 seconds. A resumed scrub
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will continue from the last saved position.
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Scrub can be started only on a mounted filesystem, though it's possible to
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scrub only a selected device. See **scrub start** for more.
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SUBCOMMAND
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----------
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cancel <path>|<device>
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If a scrub is running on the filesystem identified by *path* or
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*device*, cancel it.
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If a *device* is specified, the corresponding filesystem is found and
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**btrfs scrub cancel** behaves as if it was called on that filesystem.
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The progress is saved in the status file so **btrfs scrub resume** can
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continue from the last position.
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resume [-BdqrR] [-c <ioprio_class> -n <ioprio_classdata>] <path>|<device>
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Resume a cancelled or interrupted scrub on the filesystem identified by
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*path* or on a given *device*. The starting point is read from the
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status file if it exists.
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This does not start a new scrub if the last scrub finished successfully.
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``Options``
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see **scrub start**.
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start [-BdqrRf] [-c <ioprio_class> -n <ioprio_classdata>] <path>|<device>
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Start a scrub on all devices of the mounted filesystem identified by
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*path* or on a single *device*. If a scrub is already running, the new
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one will not start. A device of an unmounted filesystem cannot be
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scrubbed this way.
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Without options, scrub is started as a background process. The
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automatic repairs of damaged copies is performed by default for block
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group profiles with redundancy.
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The default IO priority of scrub is the idle class. The priority can be
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configured similar to the ``ionice(1)`` syntax using *-c* and *-n*
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options. Note that not all IO schedulers honor the ionice settings.
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``Options``
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-B
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do not background and print scrub statistics when finished
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-d
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print separate statistics for each device of the filesystem
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(*-B* only) at the end
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-r
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run in read-only mode, do not attempt to correct anything, can
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be run on a read-only filesystem
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-R
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raw print mode, print full data instead of summary
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-c <ioprio_class>
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set IO priority class (see ``ionice(1)`` manpage)
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-n <ioprio_classdata>
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set IO priority classdata (see ``ionice(1)`` manpage)
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-f
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force starting new scrub even if a scrub is already running,
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this can useful when scrub status file is damaged and reports a
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running scrub although it is not, but should not normally be
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necessary
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-q
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(deprecated) alias for global *-q* option
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status [options] <path>|<device>
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Show status of a running scrub for the filesystem identified by *path*
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or for the specified *device*.
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If no scrub is running, show statistics of the last finished or
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cancelled scrub for that filesystem or device.
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``Options``
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-d
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print separate statistics for each device of the filesystem
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-R
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print all raw statistics without postprocessing as returned by
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the status ioctl
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--raw
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print all numbers raw values in bytes without the *B* suffix
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--human-readable
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print human friendly numbers, base 1024, this is the default
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--iec
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select the 1024 base for the following options, according to
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the IEC standard
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--si
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select the 1000 base for the following options, according to the SI standard
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--kbytes
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show sizes in KiB, or kB with --si
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--mbytes
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show sizes in MiB, or MB with --si
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--gbytes
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show sizes in GiB, or GB with --si
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--tbytes
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show sizes in TiB, or TB with --si
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EXIT STATUS
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-----------
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**btrfs scrub** returns a zero exit status if it succeeds. Non zero is
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returned in case of failure:
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1
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scrub couldn't be performed
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2
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there is nothing to resume
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3
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scrub found uncorrectable errors
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AVAILABILITY
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------------
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**btrfs** is part of btrfs-progs.
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Please refer to the btrfs wiki http://btrfs.wiki.kernel.org for
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further details.
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SEE ALSO
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--------
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``mkfs.btrfs(8)``,
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``ionice(1)``
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