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).

       -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.

SEE ALSO

       btrfs(5), btrfs-balance(8), mkfs.btrfs(8)