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 . 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).
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. -x:: (since
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). -n:: (since
Enable no-holes feature (more efficient representation of file
holes), enabled by mkfs feature no-holes. -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.
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 abase 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.
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 2017-03-13. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-to-
date source for the page, or you have corrections or improvements to
the information in this COLOPHON (which is not part of the original
manual page), send a mail to firstname.lastname@example.org
Btrfs v4.6.1 12/10/2016 BTRFSTUNE(8)