BTRFSTUNE(8) BTRFS BTRFSTUNE(8)
NAME
btrfstune - tune various filesystem parameters
SYNOPSIS
btrfstune [options] <device> [<device>...]
DESCRIPTION
btrfstune can be used to enable, disable, or set various filesystem pa-
rameters. The filesystem must be unmounted.
The common use case 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 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
-b (since kernel 6.1, needs experimental build of btrfs-progs) En-
able block group tree feature (greatly reduce mount time), en-
abled by mkfs feature block-group-tree.
-f Allow dangerous changes, e.g. clear the seeding flag or change
fsid. Make sure that you are aware of the dangers.
-m (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 re-
mains 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.
-n (since kernel: 3.14)
Enable no-holes feature (more efficient representation of file
holes), enabled by mkfs feature no-holes.
-r (since kernel: 3.7)
Enable extended inode refs (hardlink limit per file in a direc-
tory 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).
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 make it seeding
again, provided that it's OK to throw away all filesystems
built on top of the previous base.
-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' 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 un-
finished 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.
WARNING:
Cancelling or interrupting a UUID change operation will make
the filesystem temporarily unmountable. To fix it, rerun
btrfstune -u and let it complete.
-x (since kernel: 3.10)
Enable skinny metadata extent refs (more efficient representa-
tion 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
btrfstune returns 0 if no error happened, 1 otherwise.
COMPATIBILITY NOTE
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
btrfs(5), btrfs-balance(8), mkfs.btrfs(8)
6.2 Feb 28, 2023 BTRFSTUNE(8)
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