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BTRFSTUNE(8)                                         Btrfs Manual                                        BTRFSTUNE(8)



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



Btrfs v4.4.1                                          11/05/2016                                         BTRFSTUNE(8)