BTRFS-CHECK(8) Btrfs Manual BTRFS-CHECK(8)
NAME
btrfs-check - check or repair a btrfs filesystem
SYNOPSIS
btrfs check [options] <device>
DESCRIPTION
The filesystem checker is used to verify structural integrity of a
filesystem and attempt to repair it if requested. It is recommended to
unmount the filesystem prior to running the check, but it is possible
to start checking a mounted filesystem (see --force).
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 do so by a developer
or an experienced user, and then only after having accepted that no
fsck successfully repair all types of filesystem corruption. Eg.
some other software or hardware bugs can fatally damage a volume.
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. Check the modes that can also
affect that.
SAFE OR ADVISORY OPTIONS
-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, and 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
-Q|--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
destroys 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.
DANGEROUS OPTIONS
--repair
enable the repair mode and attempt to fix problems where possible
Note
there's a warning and 10 second delay when this option is run
without --force to give users a chance to think twice before
running repair, the warnings in documentation have shown to be
insufficient
--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
The metadata are read into memory and verified, thus the
requirements are high on large filesystems and can even lead to
out-of-memory conditions. The possible workaround is to export
the block device over network to a machine with enough memory.
lowmem
This mode is supposed to address the high memory consumption at
the cost of increased IO when it needs to re-read blocks. This
may increase run time.
Note
lowmem mode does not work with --repair yet, and is still
considered experimental.
--force
allow work on a mounted filesystem. Note that this should work fine
on a quiescent or read-only mounted filesystem but may crash if the
device is changed externally, eg. by the kernel module. Repair
without mount checks is not supported right now.
This option also skips the delay and warning in the repair mode
(see --repair).
EXIT STATUS
btrfs check returns a zero exit status if it succeeds. Non zero is
returned in case of failure.
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), btrfs-scrub(8), btrfs-rescue(8)
Btrfs v5.7 07/02/2020 BTRFS-CHECK(8)