Manpage/btrfs-check

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=btrfs-check(8) manual page=
 +
{{GeneratedManpage
 +
|name=btrfs-check}}
  
=btrfs-check(8) Manual Page=
+
==NAME==
{{GeneratedManpage}}
+
btrfs-check - check or repair a btrfs filesystem
  
 +
==SYNOPSIS==
  
==NAME==
+
<p><b>btrfs check</b> [options] <em>&lt;device&gt;</em></p>
 +
==DESCRIPTION==
  
btrfs-check - check or repair an unmounted btrfs filesystem
+
<p>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 <em>--force</em>).</p>
 +
<p>By default, <b>btrfs check</b> will not modify the device but you can reaffirm that
 +
by the option <em>--readonly</em>.</p>
 +
<p><b>btrfsck</b> is an alias of <b>btrfs check</b> command and is now deprecated.</p>
 +
<blockquote><b>Warning:</b>
 +
Do not use <em>--repair</em> unless you are advised to by a developer, an
 +
experienced user or accept the fact that <em>fsck</em> cannot possibly fix all sorts
 +
of damage that could happen to a filesystem because of software and hardware
 +
bugs.</blockquote>
 +
<p>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.</p>
 +
<p>There are several cross checks that can detect wrong reference counts of shared
 +
extents, backreferences, missing extents of inodes, directory and inode
 +
connectivity etc.</p>
 +
<p>The amount of memory required can be high, depending on the size of the
 +
filesystem, similarly the run time.</p>
 +
==SAFE OR ADVISORY OPTIONS==
  
==SYNOPSIS==
+
<dl>
 +
<dt>
 +
-b|--backup
 +
<dd>
 +
<p>
 +
use the first valid set of backup roots stored in the superblock
 +
</p>
 +
<p>This can be combined with <em>--super</em> if some of the superblocks are damaged.</p>
  
'''btrfs check''' [options] &lt;device&gt;
+
<dt>
 +
--check-data-csum
 +
<dd>
 +
<p>
 +
verify checksums of data blocks
 +
</p>
 +
<p>This expects that the filesystem is otherwise
 +
OK, so this is basically and offline <em>scrub</em> but does not repair data from
 +
spare copies.</p>
  
==DESCRIPTION==
+
<dt>
 +
--chunk-root <em>&lt;bytenr&gt;</em>
 +
<dd>
 +
<p>
 +
use the given offset <em>bytenr</em> for the chunk tree root
 +
</p>
  
'''btrfs check''' is used to check or repair an unmounted btrfs filesystem.
+
<dt>
 +
-E|--subvol-extents <em>&lt;subvolid&gt;</em>
 +
<dd>
 +
<p>
 +
show extent state for the given subvolume
 +
</p>
  
'''Note:''' Since btrfs is under development, the '''btrfs check''' capabilities are continuously enhanced. It’s highly recommended to read the following btrfs wiki before executing '''btrfs check''' with '''--repair''' option:<br />https://btrfs.wiki.kernel.org/index.php/Btrfsck
+
<dt>
 +
-p|--progress
 +
<dd>
 +
<p>
 +
indicate progress at various checking phases
 +
</p>
  
'''btrfsck''' is an alias of '''btrfs check''' command and is now deprecated.
+
<dt>
 +
-Q|--qgroup-report
 +
<dd>
 +
<p>
 +
verify qgroup accounting and compare against filesystem accounting
 +
</p>
  
==OPTIONS==
+
<dt>
 +
-r|--tree-root <em>&lt;bytenr&gt;</em>
 +
<dd>
 +
<p>
 +
use the given offset <em>bytenr</em> for the tree root
 +
</p>
  
; -s|--super &lt;superblock&gt;
+
<dt>
: use &lt;superblock&gt;th superblock copy, valid values are 0 up to 2 if the respective superblock offset is within the fileystem
+
--readonly
; --repair
+
<dd>
: try to repair the filesystem
+
<p>
; --init-csum-tree
+
(default)
: create a new CRC tree and recalculate all checksums
+
run in read-only mode, this option exists to calm potential panic when users
; --init-extent-tree
+
are going to run the checker
: create a new extent tree
+
</p>
; --check-data-csum
+
: verify checkums of data blocks
+
; --qgroup-report
+
: verify qgroup accounting and compare against filesystem accounting
+
; --subvol-extents &lt;subvolid&gt;
+
: show extent state for a subvolume
+
; --tree-root &lt;bytenr&gt;
+
: use the given bytenr for the tree root
+
  
==EXIT STATUS==
+
<dt>
 +
-s|--super <em>&lt;superblock&gt;</em>
 +
<dd>
 +
<p>
 +
use 'superblock&#8217;th superblock copy, valid values are 0, 1 or 2 if the
 +
respective superblock offset is within the device size
 +
</p>
 +
<p>This can be used to use a different starting point if some of the primary
 +
superblock is damaged.</p>
  
'''btrfs check''' returns a zero exit status if it succeeds. Non zero is returned in case of failure.
+
<dt>
 +
--clear-space-cache v1|v2
 +
<dd>
 +
<p>
 +
completely wipe all free space cache of given type
 +
</p>
 +
<p>For free space cache <em>v1</em>, the <em>clear_cache</em> 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 <em>v1</em> makes it possible
 +
to actually clear the entire free space cache.</p>
 +
<p>For free space cache <em>v2</em>, the <em>clear_cache</em> kernel mount option does destroy
 +
the entire free space cache. This option with <em>v2</em> provides an alternative
 +
method of clearing the free space cache that doesn&#8217;t require mounting the
 +
filesystem.</p>
  
==AVAILABILITY==
+
</dl>
 +
==DANGEROUS OPTIONS==
  
'''btrfs''' is part of btrfs-progs. Please refer to the btrfs wiki http://btrfs.wiki.kernel.org for further details.
+
<dl>
 +
<dt>
 +
--repair
 +
<dd>
 +
<p>
 +
enable the repair mode and attempt to fix problems where possible
 +
</p>
  
==SEE ALSO==
+
<dt>
 +
--init-csum-tree
 +
<dd>
 +
<p>
 +
create a new checksum tree and recalculate checksums in all files
 +
</p>
 +
<blockquote><b>Note:</b>
 +
Do not blindly use this option to fix checksum mismatch problems.</blockquote>
  
[[Manpage/mkfs.btrfs|mkfs.btrfs(8)]], [[Manpage/btrfs-scrub|btrfs-scrub(8)]], [[Manpage/btrfs-rescue|btrfs-rescue(8)]]
+
<dt>
 +
--init-extent-tree
 +
<dd>
 +
<p>
 +
build the extent tree from scratch
 +
</p>
 +
<blockquote><b>Note:</b>
 +
Do not use unless you know what you&#8217;re doing.</blockquote>
  
 +
<dt>
 +
--mode=MODE
 +
<dd>
 +
<p>
 +
select mode of operation regarding memory and IO
 +
</p>
 +
<p>The <em>MODE</em> can be one of <em>original</em> and <em>lowmem</em>. 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.</p>
 +
 +
</dl>
 +
<blockquote><b>Note:</b>
 +
<em>lowmem</em> mode does not work with <em>--repair</em> yet, and is still considered
 +
experimental.</blockquote>
 +
<dl>
 +
<dt>
 +
--force
 +
<dd>
 +
<p>
 +
allow to 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.
 +
</p>
 +
 +
</dl>
 +
==EXIT STATUS==
 +
 +
<p><b>btrfs check</b> returns a zero exit status if it succeeds. Non zero is
 +
returned in case of failure.</p>
 +
==AVAILABILITY==
 +
 +
<p><b>btrfs</b> is part of btrfs-progs.
 +
Please refer to the btrfs wiki http://btrfs.wiki.kernel.org for
 +
further details.</p>
 +
==SEE ALSO==
  
 +
<p>[[Manpage/mkfs.btrfs|mkfs.btrfs(8)]],
 +
[[Manpage/btrfs-scrub|btrfs-scrub(8)]],
 +
[[Manpage/btrfs-rescue|btrfs-rescue(8)]]</p>
 
[[Category:Manpage]]
 
[[Category:Manpage]]

Latest revision as of 20:35, 29 September 2017

Contents

[edit] btrfs-check(8) manual page

Warning: this page is automatically generated from git, all edits will be lost. Current git version.


[edit] NAME

btrfs-check - check or repair a btrfs filesystem

[edit] SYNOPSIS

btrfs check [options] <device>

[edit] 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 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.

[edit] 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, 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

-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 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.

[edit] DANGEROUS OPTIONS

--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.

--force

allow to 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.

[edit] EXIT STATUS

btrfs check returns a zero exit status if it succeeds. Non zero is returned in case of failure.

[edit] AVAILABILITY

btrfs is part of btrfs-progs. Please refer to the btrfs wiki http://btrfs.wiki.kernel.org for further details.

[edit] SEE ALSO

mkfs.btrfs(8), btrfs-scrub(8), btrfs-rescue(8)

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