Provided by: btrfs-tools_4.4-1_i386 bug


       btrfstune - tune various filesystem parameters


       btrfstune [options] <dev> [<dev>...]


       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 .


       -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.

           Enable extended inode refs (hardlink limit per file in a directory
           is 65536), enabled by mkfs feature extref. Since kernel 3.7.

           Enable skinny metadata extent refs (more efficient representation
           of extents), enabled by mkfs feature skinny-metadata. Since kernel

           Enable no-holes feature (more efficient representation of file
           holes), enabled by mkfs feature no-holes. Since kernel 3.14.

           Allow dangerous changes, e.g. clear the seeding flag or change
           fsid. Make sure that you are aware of the dangers.

           Change fsid to a randomly generated UUID or continue previous fsid
           change operation in case it was interrupted.

       -U <UUID>
           Change fsid to UUID.

           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.

           Cancelling or interrupting a UUID change operation will make the
           filesystem temporarily unmountable. To fix it, rerun btrfstune -u
           to restore the UUID and let it complete.

           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.


       btrfstune returns 0 if no error happened, 1 otherwise.


       This tool exists for historical reasons but is still in use today. The
       functionality is about to be merged to the main tool someday and
       btrfstune will become deprecated and removed afterwards.