80 lines
3.3 KiB
Plaintext
80 lines
3.3 KiB
Plaintext
$FreeBSD$
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UFS Access Control Lists Copyright
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The UFS Access Control Lists implementation is copyright Robert Watson,
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and is made available under a Berkeley-style license.
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About UFS Access Control Lists (ACLs)
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Access control lists allow the association of fine-grained discretionary
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access control information with files and directories, extending the
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base UNIX permission model in a (mostly) compatible way. This
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implementation largely follows the POSIX.1e model, and relies on the
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availability of extended attributes to store extended components of
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the ACL, while maintaining the base permission information in the inode.
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Using UFS Access Control Lists (ACLs)
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Support for UFS access control lists may be enabled by adding:
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options UFS_ACL
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to your kernel configuration. As ACLs rely on the availability of extended
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attributes, your file systems must have support for extended attributes.
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For UFS2, this is supported natively, so no further configuration is
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necessary. For UFS1, you must also enable the optional extended attributes
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support documented in README.extattr. A summary of the instructions
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and ACL-specific information follows.
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To enable support for ACLs on a file system, the 'acls' mount flag
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must be set for the file system. This may be set using the tunefs
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'-a' flag:
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tunefs -a enable /dev/md0a
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Or by using the mount-time flag:
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mount -o acls /dev/md0a /mnt
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The flag may also be set in /etc/fstab. Note that mounting a file
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system previously configured for ACLs without ACL-support will result
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in incorrect application of discretionary protections. Likewise,
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mounting an ACL-enabled file system without kernel support for ACLs
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will result in incorrect application of discretionary protections. If
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the kernel is not configured for ACL support, a warning will be
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printed by the kernel at mount-time. For reliability purposes, it
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is recommended that the superblock flag be used instead of the
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mount-time flag, as this will avoid re-mount isses with the root file
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system. For reliability and performance reasons, the use of ACLs on
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UFS1 is discouraged; UFS2 extended attributes provide a more reliable
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storage mechanism for ACLs.
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Currently, support for ACLs on UFS1 requires the use of UFS1 EAs, which may
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be enabled by adding:
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options UFS_EXTATTR
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to your kernel configuration file and rebuilding. Because of filesystem
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mount atomicity requirements, it is also recommended that:
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options UFS_EXTATTR_AUTOSTART
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be added to the kernel so as to support the atomic enabling of the
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required extended attributes with the filesystem mount operation. To
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enable ACLs, two extended attributes must be available in the
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EXTATTR_NAMESPACE_SYSTEM namespace: "posix1e.acl_access", which holds
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the access ACL, and "posix1e.acl_default" which holds the default ACL
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for directories. If you're using UFS1 Extended Attributes, the following
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commands may be used to create the necessary EA backing files for
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ACLs in the filesystem root of each filesystem. In these examples,
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the root filesystem is used; see README.extattr for more details.
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mkdir -p /.attribute/system
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cd /.attribute/system
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extattrctl initattr -p / 388 posix1e.acl_access
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extattrctl initattr -p / 388 posix1e.acl_default
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On the next mount of the root filesystem, the attributes will be
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automatically started, and ACLs will be enabled.
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