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NAME | SYNOPSIS | DESCRIPTION | SAFE OR ADVISORY OPTIONS | DANGEROUS OPTIONS | EXIT STATUS | AVAILABILITY | SEE ALSO | COLOPHON |
BTRFS-CHECK(8) Btrfs Manual BTRFS-CHECK(8)
btrfs-check - check or repair an unmounted btrfs filesystem
btrfs check [options] <device>
The filesystem checker is used to verify structural integrity of a
filesystem and attempt to repair it if requested. The filesystem must
be unmounted.
By default, btrfs check will not modify the device but you can
reaffirm that by the option --readonly.
btrfsck is an alias of btrfs check command and is now deprecated.
Warning
Do not use --repair unless you are advised to by a developer, an
experienced user or accept the fact that fsck cannot possibly fix
all sorts of damage that could happen to a filesystem because of
software and hardware bugs.
The structural integrity check verifies if internal filesystem
objects or data structures satisfy the constraints, point to the
right objects or are correctly connected together.
There are several cross checks that can detect wrong reference counts
of shared extents, backreferences, missing extents of inodes,
directory and inode connectivity etc.
The amount of memory required can be high, depending on the size of
the filesystem, similarly the run time.
-b|--backup
use the first valid set of backup roots stored in the superblock
This can be combined with --super if some of the superblocks are
damaged.
--check-data-csum
verify checksums of data blocks
This expects that the filesystem is otherwise OK, so this is
basically and offline scrub but does not repair data from spare
copies.
--chunk-root <bytenr>
use the given offset bytenr for the chunk tree root
-E|--subvol-extents <subvolid>
show extent state for the given subvolume
-p|--progress
indicate progress at various checking phases
--qgroup-report
verify qgroup accounting and compare against filesystem
accounting
-r|--tree-root <bytenr>
use the given offset bytenr for the tree root
--readonly
(default) run in read-only mode, this option exists to calm
potential panic when users are going to run the checker
-s|--super <superblock>
use 'superblock’th superblock copy, valid values are 0, 1 or 2 if
the respective superblock offset is within the device size
This can be used to use a different starting point if some of the
primary superblock is damaged.
--clear-space-cache v1|v2
completely wipe all free space cache of given type
For free space cache v1, the clear_cache kernel mount option only
rebuilds the free space cache for block groups that are modified
while the filesystem is mounted with that option. Thus, using
this option with v1 makes it possible to actually clear the
entire free space cache.
For free space cache v2, the clear_cache kernel mount option does
destroy the entire free space cache. This option with v2 provides
an alternative method of clearing the free space cache that
doesn’t require mounting the filesystem.
--repair
enable the repair mode and attempt to fix problems where possible
--init-csum-tree
create a new checksum tree and recalculate checksums in all files
Note
Do not blindly use this option to fix checksum mismatch
problems.
--init-extent-tree
build the extent tree from scratch
Note
Do not use unless you know what you’re doing.
--mode=MODE
select mode of operation regarding memory and IO
The MODE can be one of original and lowmem. The original mode is
mostly unoptimized regarding memory consumption and can lead to
out-of-memory conditions on large filesystems. The possible
workaround is to export the block device over network to a
machine with enough memory. The low memory mode is supposed to
address the memory consumption, at the cost of increased IO when
it needs to re-read blocks when needed. This may increase run
time.
Note
lowmem mode does not work with --repair yet, and is still
considered experimental.
btrfs check returns a zero exit status if it succeeds. Non zero is
returned in case of failure.
btrfs is part of btrfs-progs. Please refer to the btrfs wiki
http://btrfs.wiki.kernel.org for further details.
mkfs.btrfs(8), btrfs-scrub(8), btrfs-rescue(8)
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 2017-07-05. 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 man-pages@man7.org
Btrfs v4.6.1 03/12/2017 BTRFS-CHECK(8)
Pages that refer to this page: btrfs(8), btrfs-rescue(8), btrfs-restore(8), fsck.btrfs(8)