btrfstune(8) — Linux manual page


BTRFSTUNE(8)                    Btrfs Manual                    BTRFSTUNE(8)

NAME         top

       btrfstune - tune various filesystem parameters

SYNOPSIS         top

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

DESCRIPTION         top

       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

       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         top

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

           (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.

           (since kernel: 3.14)

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

           (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.

               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.

           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.

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

           (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         top

       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

SEE ALSO         top

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

COLOPHON         top

       This page is part of the btrfs-progs (btrfs filesystem tools)
       project.  Information about the project can be found at 
       If you have a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       on 2020-09-18.  (At that time, the date of the most recent commit
       that was found in the repository was 2020-07-02.)  If you discover
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       COLOPHON (which is not part of the original manual page), send a mail

Btrfs v4.6.1                     05/16/2020                     BTRFSTUNE(8)

Pages that refer to this page: btrfs(8)