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)

6.6.3                                             Jun 12, 2024                                      BTRFSTUNE(8)