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 features.

       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

           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. See also section
           SEEDING DEVICE in btrfs(5).

               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

               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

               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

           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 removal.

SEE ALSO         top

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

COLOPHON         top

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       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 2024-06-14.  (At that time, the date of the most recent commit
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Btrfs v5.16.1                  02/06/2022                   BTRFSTUNE(8)

Pages that refer to this page: btrfs(8)