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 enabled on a mounted filesystem. Please
       refer to the respective section in btrfs(5).

OPTIONS         top

       -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.

           (since kernel: 3.7)

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

           (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).

           (since kernel: 3.14)

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

           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.

EXIT STATUS         top

       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.

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 2017-09-15.  If you discover any rendering problems in this HTML
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       manual page), send a mail to

Btrfs v4.6.1                     07/05/2017                     BTRFSTUNE(8)

Pages that refer to this page: btrfs(8)