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NAME | SYNOPSIS | DESCRIPTION | SUBCOMMAND | EXIT STATUS | AVAILABILITY | SEE ALSO | COLOPHON |
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BTRFS-SCRUB(8) Btrfs Manual BTRFS-SCRUB(8)
btrfs-scrub - scrub btrfs filesystem, verify block checksums
btrfs scrub <subcommand> <args>
btrfs scrub is used to scrub a mounted 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.
Scrub can be started only on a mounted filesystem, though it’s
possible to scrub only a selected device. See scrub start for
more.
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
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
btrfs is part of btrfs-progs. Please refer to the btrfs wiki
http://btrfs.wiki.kernel.org for further details.
mkfs.btrfs(8), ionice(1)
This page is part of the btrfs-progs (btrfs filesystem tools)
project. Information about the project can be found at
⟨https://btrfs.wiki.kernel.org/index.php/Btrfs_source_repositories⟩.
If you have a bug report for this manual page, see
⟨https://btrfs.wiki.kernel.org/index.php/Problem_FAQ#How_do_I_report_bugs_and_issues.3F⟩.
This page was obtained from the project's upstream Git repository
⟨git://git.kernel.org/pub/scm/linux/kernel/git/kdave/btrfs-progs.git⟩
on 2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-06-23.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to [email protected]
Btrfs v5.16.1 02/06/2022 BTRFS-SCRUB(8)
Pages that refer to this page: btrfs(8), btrfs-check(8), btrfs-rescue(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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