1BTRFSTUNE(8) Btrfs Manual BTRFSTUNE(8)
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6 btrfstune - tune various filesystem parameters
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9 btrfstune [options] <device> [<device>...]
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12 btrfstune can be used to enable, disable, or set various filesystem
13 parameters. The filesystem must be unmounted.
14 The common usecase is to enable features that were not enabled at mkfs
16 time. Please make sure that you have kernel support for the features.
17 You can find a complete list of features and kernel version of their
18 introduction at
19 https://btrfs.wiki.kernel.org/index.php/Changelog#By_feature . Also,
20 the manual page mkfs.btrfs(8) contains more details about the features.
21 Some of the features could be also enabled on a mounted filesystem by
23 other means. Please refer to the FILESYSTEM FEATURES in btrfs(5).
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26 -f
27 Allow dangerous changes, e.g. clear the seeding flag or change
28 fsid. Make sure that you are aware of the dangers.
29 -m
31 (since kernel: 5.0)
32 change fsid stored as metadata_uuid to a randomly generated UUID,
34 see also -U
35 -M <UUID>
37 (since kernel: 5.0)
38 change fsid stored as metadata_uuid to a given UUID, see also -U
40 The metadata_uuid is stored only in the superblock and is a
42 backward incompatible change. The fsid in metadata blocks remains
43 unchanged and is not overwritten, thus the whole operation is
44 significantly faster than -U.
45 The new metadata_uuid can be used for mount by UUID and is also
47 used to identify devices of a multi-device filesystem.
48 -n
50 (since kernel: 3.14)
51 Enable no-holes feature (more efficient representation of file
53 holes), enabled by mkfs feature no-holes.
54 -r
56 (since kernel: 3.7)
57 Enable extended inode refs (hardlink limit per file in a directory
59 is 65536), enabled by mkfs feature extref.
60 -S <0|1>
62 Enable seeding on a given device. Value 1 will enable seeding, 0
63 will disable it.
64 A seeding filesystem is forced to be mounted read-only. A new
66 device can be added to the filesystem and will capture all writes
67 keeping the seeding device intact. See also section SEEDING DEVICE
68 in btrfs(5).
69 Warning
71 Clearing the seeding flag on a device may be dangerous. If a
72 previously-seeding device is changed, all filesystems that used
73 that device will become unmountable. Setting the seeding flag
74 back will not fix that.
75 A valid usecase is seeding device as a base image. Clear the
77 seeding flag, update the filesystem and make it seeding again,
78 provided that it’s OK to throw away all filesystems built on
79 top of the previous base.
80 -u
82 Change fsid to a randomly generated UUID or continue previous fsid
83 change operation in case it was interrupted.
84 -U <UUID>
86 Change fsid to UUID in all metadata blocks.
87 The UUID should be a 36 bytes string in printf(3) format
89 "%08x-%04x-%04x-%04x-%012x". If there is a previous unfinished fsid
90 change, it will continue only if the UUID matches the unfinished
91 one or if you use the option -u.
92 All metadata blocks are rewritten, this may take some time, but the
94 final filesystem compatibility is unaffected, unlike -M.
95 Warning
97 Cancelling or interrupting a UUID change operation will make
98 the filesystem temporarily unmountable. To fix it, rerun
99 btrfstune -u and let it complete.
100 -x
102 (since kernel: 3.10)
103 Enable skinny metadata extent refs (more efficient representation
105 of extents), enabled by mkfs feature skinny-metadata.
106 All newly created extents will use the new representation. To
108 completely switch the entire filesystem, run a full balance of the
109 metadata. Please refer to btrfs-balance(8).
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112 btrfstune returns 0 if no error happened, 1 otherwise.
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115 This deprecated tool exists for historical reasons but is still in use
116 today. Its functionality will be merged to the main tool, at which time
117 btrfstune will be declared obsolete and scheduled for removal.
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120 btrfs(5), btrfs-balance(8), mkfs.btrfs(8)
121Btrfs v5.15.1 11/22/2021 BTRFSTUNE(8)