BTRFSTUNE(8) Btrfs Manual BTRFSTUNE(8)
NAME
btrfstune - tune various filesystem parameters
SYNOPSIS
btrfstune [options] <device> [<device>...]
DESCRIPTION
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).
OPTIONS
-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.
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).
EXIT STATUS
btrfstune returns 0 if no error happened, 1 otherwise.
COMPATIBILITY NOTE
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.
SEE ALSO
btrfs(5), btrfs-balance(8), mkfs.btrfs(8)
Btrfs v5.7 07/02/2020 BTRFSTUNE(8)