1BTRFSTUNE(8) Btrfs Manual BTRFSTUNE(8)
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6 btrfstune - tune various filesystem parameters
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9 btrfstune [options] <dev> [<dev>...]
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12 btrfstune can be used to enable, disable or set various filesystem
13 parameters. The filesystem must be unmounted.
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15 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.
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22 Some of the features could be enabled on a mounted filesystem. Please
23 refer to the respective section in btrfs(5).
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26 -S <0|1>
27 Enable seeding on a given device. Value 1 will enable seeding, 0
28 will disable it.
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30 A seeding filesystem is forced to be mounted read-only. A new
31 device can be added to the filesystem and will capture all writes
32 keeping the seeding device intact.
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34 -r
35 (since kernel: 3.7)
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37 Enable extended inode refs (hardlink limit per file in a directory
38 is 65536), enabled by mkfs feature extref. -x:: (since kernel:
39 3.10)
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41 Enable skinny metadata extent refs (more efficient representation
42 of extents), enabled by mkfs feature skinny-metadata.
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44 All newly created extents will use the new representation. To
45 completely switch the entire filesystem, run a full balance of the
46 metadata. Please refer to btrfs-balance(8). -n:: (since kernel:
47 3.14)
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49 Enable no-holes feature (more efficient representation of file
50 holes), enabled by mkfs feature no-holes. -f:: Allow dangerous
51 changes, e.g. clear the seeding flag or change fsid. Make sure that
52 you are aware of the dangers. -u:: Change fsid to a randomly
53 generated UUID or continue previous fsid change operation in case
54 it was interrupted. -U <UUID>:: Change fsid to UUID.
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56 The UUID should be a 36 bytes string in printf(3) format
57 "%08x-%04x-%04x-%04x-%012x". If there is a previous unfinished fsid
58 change, it will continue only if the UUID matches the unfinished
59 one or if you use the option -u.
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61 Warning
62 Cancelling or interrupting a UUID change operation will make the
63 filesystem temporarily unmountable. To fix it, rerun btrfstune -u
64 to restore the UUID and let it complete.
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66 Warning
67 Clearing the seeding flag on a device may be dangerous. If a
68 previously-seeding device is changed, all filesystems that used
69 that device will become unmountable. Setting the seeding flag back
70 will not fix that. A valid usecase is seeding device as a base
71 image. Clear the seeding flag, update the filesystem and make it
72 seeding again, provided that it’s OK to throw away all filesystems
73 built on top of the previous base.
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76 btrfstune returns 0 if no error happened, 1 otherwise.
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79 This tool exists for historical reasons but is still in use today. The
80 functionality is about to be merged to the main tool someday and
81 btrfstune will become deprecated and removed afterwards.
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84 btrfs(5), btrfs-balance(8), mkfs.btrfs(8)
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88Btrfs v4.9.1 08/06/2017 BTRFSTUNE(8)