1BTRFSTUNE(8) BTRFS 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 pa‐
13 rameters. The filesystem must be unmounted.
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15 The common use case 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.
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22 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 -b (since kernel 6.1, needs experimental build of btrfs-progs) En‐
27 able block group tree feature (greatly reduce mount time), en‐
28 abled by mkfs feature block-group-tree.
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30 -f Allow dangerous changes, e.g. clear the seeding flag or change
31 fsid. Make sure that you are aware of the dangers.
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33 -m (since kernel: 5.0)
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35 change fsid stored as 'metadata_uuid' to a randomly generated
36 UUID, see also '-U'
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38 -M <UUID>
39 (since kernel: 5.0)
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41 change fsid stored as metadata_uuid to a given UUID, see also -U
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43 The metadata_uuid is stored only in the superblock and is a
44 backward incompatible change. The fsid in metadata blocks re‐
45 mains unchanged and is not overwritten, thus the whole operation
46 is significantly faster than -U.
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48 The new metadata_uuid can be used for mount by UUID and is also
49 used to identify devices of a multi-device filesystem.
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51 -n (since kernel: 3.14)
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53 Enable no-holes feature (more efficient representation of file
54 holes), enabled by mkfs feature no-holes.
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56 -r (since kernel: 3.7)
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58 Enable extended inode refs (hardlink limit per file in a direc‐
59 tory is 65536), enabled by mkfs feature extref.
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61 -S <0|1>
62 Enable seeding on a given device. Value 1 will enable seeding, 0
63 will disable it. A seeding filesystem is forced to be mounted
64 read-only. A new device can be added to the filesystem and will
65 capture all writes keeping the seeding device intact. See also
66 section SEEDING DEVICE in btrfs(5).
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68 WARNING:
69 Clearing the seeding flag on a device may be dangerous. If a
70 previously-seeding device is changed, all filesystems that
71 used that device will become unmountable. Setting the seeding
72 flag back will not fix that.
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74 A valid usecase is 'seeding device as a base image'. Clear
75 the seeding flag, update the filesystem and make it seeding
76 again, provided that it's OK to throw away all filesystems
77 built on top of the previous base.
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79 -u Change fsid to a randomly generated UUID or continue previous
80 fsid change operation in case it was interrupted.
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82 -U <UUID>
83 Change fsid to 'UUID' in all metadata blocks.
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85 The UUID should be a 36 bytes string in printf(3) format
86 "%08x-%04x-%04x-%04x-%012x". If there is a previous unfinished
87 fsid change, it will continue only if the UUID matches the un‐
88 finished one or if you use the option -u.
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90 All metadata blocks are rewritten, this may take some time, but
91 the final filesystem compatibility is unaffected, unlike -M.
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93 WARNING:
94 Cancelling or interrupting a UUID change operation will make
95 the filesystem temporarily unmountable. To fix it, rerun
96 btrfstune -u and let it complete.
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98 -x (since kernel: 3.10)
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100 Enable skinny metadata extent refs (more efficient representa‐
101 tion of extents), enabled by mkfs feature skinny-metadata.
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103 All newly created extents will use the new representation. To
104 completely switch the entire filesystem, run a full balance of
105 the metadata. Please refer to btrfs-balance(8).
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108 btrfstune returns 0 if no error happened, 1 otherwise.
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111 This deprecated tool exists for historical reasons but is still in use
112 today. Its functionality will be merged to the main tool, at which
113 time btrfstune will be declared obsolete and scheduled for removal.
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116 btrfs(5), btrfs-balance(8), mkfs.btrfs(8)
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1216.1.3 Jan 25, 2023 BTRFSTUNE(8)