89 lines
2.9 KiB
ReStructuredText
89 lines
2.9 KiB
ReStructuredText
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The btrfs filesystem supports setting file attributes or flags. Note there are
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old and new interfaces, with confusing names. The following list should clarify
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that:
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* *attributes*: ``chattr(1)`` or ``lsattr(1)`` utilities (the ioctls are
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FS_IOC_GETFLAGS and FS_IOC_SETFLAGS), due to the ioctl names the attributes
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are also called flags
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* *xflags*: to distinguish from the previous, it's extended flags, with tunable
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bits similar to the attributes but extensible and new bits will be added in
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the future (the ioctls are FS_IOC_FSGETXATTR and FS_IOC_FSSETXATTR but they
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are not related to extended attributes that are also called xattrs), there's
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no standard tool to change the bits, there's support in ``xfs_io(8)`` as
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command **xfs_io -c chattr**
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Attributes
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^^^^^^^^^^
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a
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*append only*, new writes are always written at the end of the file
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A
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*no atime updates*
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c
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*compress data*, all data written after this attribute is set will be compressed.
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Please note that compression is also affected by the mount options or the parent
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directory attributes.
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When set on a directory, all newly created files will inherit this attribute.
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This attribute cannot be set with 'm' at the same time.
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C
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*no copy-on-write*, file data modifications are done in-place
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When set on a directory, all newly created files will inherit this attribute.
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.. note::
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Due to implementation limitations, this flag can be set/unset only on
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empty files.
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d
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*no dump*, makes sense with 3rd party tools like ``dump(8)``, on BTRFS the
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attribute can be set/unset but no other special handling is done
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D
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*synchronous directory updates*, for more details search ``open(2)`` for *O_SYNC*
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and *O_DSYNC*
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i
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*immutable*, no file data and metadata changes allowed even to the root user as
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long as this attribute is set (obviously the exception is unsetting the attribute)
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m
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*no compression*, permanently turn off compression on the given file. Any
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compression mount options will not affect this file. (``chattr`` support added in
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1.46.2)
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When set on a directory, all newly created files will inherit this attribute.
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This attribute cannot be set with *c* at the same time.
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S
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*synchronous updates*, for more details search ``open(2)`` for *O_SYNC* and
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*O_DSYNC*
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No other attributes are supported. For the complete list please refer to the
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``chattr(1)`` manual page.
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XFLAGS
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^^^^^^
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There's overlap of letters assigned to the bits with the attributes, this list
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refers to what ``xfs_io(8)`` provides:
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i
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*immutable*, same as the attribute
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a
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*append only*, same as the attribute
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s
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*synchronous updates*, same as the attribute *S*
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A
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*no atime updates*, same as the attribute
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d
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*no dump*, same as the attribute
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