BTRFSTUNE(8)			     BTRFS			  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 use case 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 Feature by version page.	 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

       --convert-to-block-group-tree
	      (since kernel 6.1)

	      Convert portions of extent tree that tracks block groups to a
	      separate block group tree. This greatly reduces mount time. Can
	      be also enabled at mkfs time.

       --convert-from-block-group-tree
	      (since kernel 6.1)

	      Convert block groups tracked in standalone block group tree back
	      to extent tree and remove block-group-tree feature bit from the
	      filesystem.

       --convert-to-free-space-tree
	      (since kernel 4.5)

	      Convert to free-space-tree feature (v2 of space cache).

       --enable-simple-quota
	      (since kernel 6.7)

	      Enable simple quota accounting (squota mkfs feature). This is an
	      alternative to qgroups with a smaller performance impact but no
	      notion of shared vs. exclusive usage.

       --remove-simple-quota
	      Remove simple quota accounting related structures.

       -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).

       --version
	      Print the btrfstune version, builtin features and exit.

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)

6.16.1			      September 10, 2025		  BTRFSTUNE(8)