btrfs-progs/Documentation/btrfs-scrub.asciidoc

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.

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 filesytem. The IO priority class is by
default 'idle' so background scrub should not interfere with normal filesystem
operation significantly.

The scrubbing status is recorded in '/var/lib/btrfs/' in textual files named
'scrub.status.UUID' for a filesystem identified by the given UUID. (An
itermediate progress is communicated through a named pipe in file
'scrub.progress.UUID' in the same directory.) The status file is updated
periodically every 5 seconds. An resumed scrub will continue from the last
saved position.

SUBCOMMAND
----------
*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.
+
`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 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.
+
`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
-q::::
be quiet, omit error messages and statistics
-r::::
run in read-only mode, do not attempt to correct anything, can be run on a read-only
filesystem
-R::::
print raw statistics per-device instead of a 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

*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)