129 lines
4.3 KiB
ReStructuredText
129 lines
4.3 KiB
ReStructuredText
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btrfstune(8)
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============
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SYNOPSIS
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--------
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**btrfstune** [options] <device> [<device>...]
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DESCRIPTION
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-----------
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**btrfstune** can be used to enable, disable, or set various filesystem
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parameters. The filesystem must be unmounted.
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The common usecase is to enable features that were not enabled at mkfs time.
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Please make sure that you have kernel support for the features. You can find a
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complete list of features and kernel version of their introduction at
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https://btrfs.wiki.kernel.org/index.php/Changelog#By_feature . Also, the
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manual page ``mkfs.btrfs(8)`` contains more details about the features.
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Some of the features could be also enabled on a mounted filesystem by other
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means. Please refer to the *FILESYSTEM FEATURES* in ``btrfs(5)``.
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OPTIONS
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-------
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-f
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Allow dangerous changes, e.g. clear the seeding flag or change fsid.
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Make sure that you are aware of the dangers.
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-m
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(since kernel: 5.0)
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change fsid stored as 'metadata_uuid' to a randomly generated UUID,
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see also '-U'
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-M <UUID>
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(since kernel: 5.0)
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change fsid stored as *metadata_uuid* to a given UUID, see also *-U*
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The metadata_uuid is stored only in the superblock and is a backward
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incompatible change. The fsid in metadata blocks remains unchanged and
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is not overwritten, thus the whole operation is significantly faster
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than *-U*.
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The new metadata_uuid can be used for mount by UUID and is also used to
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identify devices of a multi-device filesystem.
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-n
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(since kernel: 3.14)
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Enable no-holes feature (more efficient representation of file holes),
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enabled by mkfs feature *no-holes*.
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-r
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(since kernel: 3.7)
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Enable extended inode refs (hardlink limit per file in a directory is
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65536), enabled by mkfs feature *extref*.
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-S <0|1>
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Enable seeding on a given device. Value 1 will enable seeding, 0 will
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disable it. A seeding filesystem is forced to be mounted read-only. A
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new device can be added to the filesystem and will capture all writes
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keeping the seeding device intact. See also section *SEEDING DEVICE*
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in ``btrfs(5)``.
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.. warning::
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Clearing the seeding flag on a device may be dangerous. If a
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previously-seeding device is changed, all filesystems that used
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that device will become unmountable. Setting the seeding flag
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back will not fix that.
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A valid usecase is 'seeding device as a base image'. Clear the
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seeding flag, update the filesystem and make it seeding again,
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provided that it's OK to throw away all filesystems built on
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top of the previous base.
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-u
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Change fsid to a randomly generated UUID or continue previous fsid
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change operation in case it was interrupted.
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-U <UUID>
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Change fsid to 'UUID' in all metadata blocks.
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The *UUID* should be a 36 bytes string in ``printf(3)`` format
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*"%08x-%04x-%04x-%04x-%012x"*.
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If there is a previous unfinished fsid change, it will continue only if the
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*UUID* matches the unfinished one or if you use the option *-u*.
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All metadata blocks are rewritten, this may take some time, but the final
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filesystem compatibility is unaffected, unlike *-M*.
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.. warning::
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Cancelling or interrupting a UUID change operation will make
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the filesystem temporarily unmountable. To fix it, rerun
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*btrfstune -u* and let it complete.
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-x
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(since kernel: 3.10)
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Enable skinny metadata extent refs (more efficient representation of
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extents), enabled by mkfs feature *skinny-metadata*.
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All newly created extents will use the new representation. To
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completely switch the entire filesystem, run a full balance of the
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metadata. Please refer to ``btrfs-balance(8)``.
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EXIT STATUS
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-----------
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**btrfstune** returns 0 if no error happened, 1 otherwise.
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COMPATIBILITY NOTE
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------------------
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This deprecated tool exists for historical reasons but is still in use today.
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Its functionality will be merged to the main tool, at which time **btrfstune**
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will be declared obsolete and scheduled for removal.
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SEE ALSO
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--------
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``btrfs(5)``,
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``btrfs-balance(8)``,
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``mkfs.btrfs(8)``
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