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
       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

       -b     (since kernel 6.1, needs experimental build of btrfs-progs) Enable block group tree
              feature (greatly reduce mount time), enabled by mkfs feature block-group-tree.

       -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)