Provided by: btrfs-progs_5.19-1_amd64 bug


       btrfstune - tune various filesystem parameters


       btrfstune [options] <device> [<device>...]


       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  .   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).


       -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).

                 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

              All metadata blocks  are  rewritten,  this  may  take  some  time,  but  the  final
              filesystem compatibility is unaffected, unlike -M.

                 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


       btrfstune returns 0 if no error happened, 1 otherwise.


       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.


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