Ubuntu Manpage: btrfstune - tune various filesystem parameters

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.
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).

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.