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=btrfstune(8) manual page=
btrfstune - tune various filesystem parameters
<p><b>btrfstune</b> [options] <em>&lt;device&gt;</em> [<em>&lt;device&gt;</em>&#8230;]</p>
<p><b>btrfstune</b> can be used to enable, disable or set various filesystem
parameters. The filesystem must be unmounted.</p>
<p>The common usecase is to enable features that were not enabled at mkfs time.
Please make sure that you have kernel support for the features.  You can find a
complete list of features and kernel version of their introduction at .  Also, the
manual page [[Manpage/mkfs.btrfs|mkfs.btrfs(8)]] contains more details about the features.</p>
<p>Some of the features could be enabled on a mounted filesystem. Please refer to
the respective section in [[Manpage/btrfs|btrfs(5)]].</p>
-S <em>&lt;0|1&gt;</em>
Enable seeding on a given device. Value 1 will enable seeding, 0 will disable it.<br/>
A seeding filesystem is forced to be mounted read-only. A new device can be added
to the filesystem and will capture all writes keeping the seeding device intact.
(since kernel: 3.7)
<p>Enable extended inode refs (hardlink limit per file in a directory is 65536),
enabled by mkfs feature <em>extref</em>.</p>
(since kernel: 3.10)
<p>Enable skinny metadata extent refs (more efficient representation of extents),
enabled by mkfs feature <em>skinny-metadata</em>.</p>
<p>All newly created extents will use the new representation. To completely switch
the entire filesystem, run a full balance of the metadata. Please refer to
(since kernel: 3.14)
<p>Enable no-holes feature (more efficient representation of file holes), enabled
by mkfs feature <em>no-holes</em>.</p>
Allow dangerous changes, e.g. clear the seeding flag or change fsid. Make sure
that you are aware of the dangers.
Change fsid to a randomly generated UUID or continue previous fsid change
operation in case it was interrupted.
-U <em>&lt;UUID&gt;</em>
Change fsid to <em>UUID</em>.
<p>The <em>UUID</em> should be a 36 bytes string in [ printf(3)] format
If there is a previous unfinished fsid change, it will continue only if the
<em>UUID</em> matches the unfinished one or if you use the option <em>-u</em>.</p>
Cancelling or interrupting a UUID change operation will make the
filesystem temporarily unmountable.  To fix it, rerun <em>btrfstune -u</em> to restore
the UUID and let it complete.</blockquote>
Clearing the seeding flag on a device may be dangerous.
If a previously-seeding device is changed, all filesystems that used that
device will become unmountable. Setting the seeding flag back will not fix
A valid usecase is <em>seeding device as a base image</em>. Clear the seeding
flag, update the filesystem and make it seeding again, provided that it&#8217;s OK
to throw away all filesystems built on top of the previous base.</blockquote>
<p><b>btrfstune</b> returns 0 if no error happened, 1 otherwise.</p>
<p>This tool exists for historical reasons but is still in use today.  The
functionality is about to be merged to the main tool someday and <b>btrfstune</b>
will become deprecated and removed afterwards.</p>

Latest revision as of 12:34, 12 January 2022

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