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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | COMPATIBILITY NOTE | SEE ALSO | COLOPHON |
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BTRFSTUNE(8) Btrfs Manual BTRFSTUNE(8)
btrfstune - tune various filesystem parameters
btrfstune [options] <device> [<device>...]
btrfstune can be used to enable, disable, or set various
filesystem parameters. The filesystem must be unmounted.
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
https://btrfs.wiki.kernel.org/index.php/Changelog#By_feature .
Also, the manual page mkfs.btrfs(8) contains more details about
the features.
Some of the features could be also enabled on a mounted filesystem
by other means. Please refer to the FILESYSTEM FEATURES in
btrfs(5).
-f
Allow dangerous changes, e.g. clear the seeding flag or change
fsid. Make sure that you are aware of the dangers.
-m
(since kernel: 5.0)
change fsid stored as metadata_uuid to a randomly generated
UUID, see also -U
-M <UUID>
(since kernel: 5.0)
change fsid stored as metadata_uuid to a given UUID, see also
-U
The metadata_uuid is stored only in the superblock and is a
backward incompatible change. The fsid in metadata blocks
remains unchanged and is not overwritten, thus the whole
operation is significantly faster than -U.
The new metadata_uuid can be used for mount by UUID and is
also used to identify devices of a multi-device filesystem.
-n
(since kernel: 3.14)
Enable no-holes feature (more efficient representation of file
holes), enabled by mkfs feature no-holes.
-r
(since kernel: 3.7)
Enable extended inode refs (hardlink limit per file in a
directory is 65536), enabled by mkfs feature extref.
-S <0|1>
Enable seeding on a given device. Value 1 will enable seeding,
0 will disable it.
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. See also section
SEEDING DEVICE in btrfs(5).
Warning
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 that.
A valid usecase is seeding device as a base image. Clear
the seeding flag, update the filesystem and make it
seeding again, provided that it’s OK to throw away all
filesystems built on top of the previous base.
-u
Change fsid to a randomly generated UUID or continue previous
fsid change operation in case it was interrupted.
-U <UUID>
Change fsid to UUID in all metadata blocks.
The UUID should be a 36 bytes string in printf(3) format
"%08x-%04x-%04x-%04x-%012x". If there is a previous unfinished
fsid change, it will continue only if the UUID matches the
unfinished one or if you use the option -u.
All metadata blocks are rewritten, this may take some time,
but the final filesystem compatibility is unaffected, unlike
-M.
Warning
Cancelling or interrupting a UUID change operation will
make the filesystem temporarily unmountable. To fix it,
rerun btrfstune -u and let it complete.
-x
(since kernel: 3.10)
Enable skinny metadata extent refs (more efficient
representation of extents), enabled by mkfs feature
skinny-metadata.
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 btrfs-balance(8).
btrfstune returns 0 if no error happened, 1 otherwise.
This deprecated tool exists for historical reasons but is still in
use today. Its functionality will be merged to the main tool, at
which time btrfstune will be declared obsolete and scheduled for
removal.
btrfs(5), btrfs-balance(8), mkfs.btrfs(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 2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-06-23.) 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 v5.16.1 02/06/2022 BTRFSTUNE(8)
Pages that refer to this page: btrfs(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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