NAME

       btrfstune - tune various filesystem parameters

SYNOPSIS

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

DESCRIPTION

       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 https://btrfs.wiki.kernel.org/index.php/Changelog#By_feature .

OPTIONS

       -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.

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

       -x
           Enable skinny metadata extent refs (more efficient representation of extents), enabled by mkfs
           feature skinny-metadata. Since kernel 3.10.

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

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

       -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.

           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.

           Warning

           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.

           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.

EXIT STATUS

       btrfstune returns 0 if no error happened, 1 otherwise.

COMPATIBILITY NOTE

       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.

SEE ALSO

       mkfs.btrfs(8)

Btrfs v4.4                                         08/13/2019                                       BTRFSTUNE(8)