123 lines
3.9 KiB
Plaintext
123 lines
3.9 KiB
Plaintext
btrfstune(8)
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============
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NAME
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----
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btrfstune - tune various filesystem parameters
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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. Make sure
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that you are aware of the dangers.
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-m::
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(since kernel: 5.0)
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+
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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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+
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change fsid stored as 'metadata_uuid' to a given UUID, see also '-U'
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+
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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 than
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'-U'.
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+
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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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+
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Enable no-holes feature (more efficient representation of file holes), enabled
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by mkfs feature 'no-holes'.
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-r::
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(since kernel: 3.7)
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+
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Enable extended inode refs (hardlink limit per file in a directory is 65536),
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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 disable it. +
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A seeding filesystem is forced to be mounted read-only. A new device can be added
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to the filesystem and will capture all writes keeping the seeding device intact.
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See also section 'SEEDING DEVICE' in `btrfs`(5).
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+
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WARNING: Clearing the seeding flag on a device may be dangerous.
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If a previously-seeding device is changed, all filesystems that used that
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device will become unmountable. Setting the seeding flag back will not fix
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that. +
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A valid usecase is 'seeding device as a base image'. Clear the seeding
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flag, update the filesystem and make it seeding again, provided that it's OK
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to throw away all filesystems built on 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 change
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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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+
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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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+
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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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+
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WARNING: Cancelling or interrupting a UUID change operation will make the
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filesystem temporarily unmountable. To fix it, rerun 'btrfstune -u' and let
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it complete.
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-x::
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(since kernel: 3.10)
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+
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Enable skinny metadata extent refs (more efficient representation of extents),
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enabled by mkfs feature 'skinny-metadata'.
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+
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All newly created extents will use the new representation. To completely switch
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the entire filesystem, run a full balance of the metadata. Please refer to
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`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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