1 2 UFS Access Control Lists Copyright 3 4The UFS Access Control Lists implementation is copyright Robert Watson, 5and is made available under a Berkeley-style license. 6 7 About UFS Access Control Lists (ACLs) 8 9Access control lists allow the association of fine-grained discretionary 10access control information with files and directories, extending the 11base UNIX permission model in a (mostly) compatible way. This 12implementation largely follows the POSIX.1e model, and relies on the 13availability of extended attributes to store extended components of 14the ACL, while maintaining the base permission information in the inode. 15 16 Using UFS Access Control Lists (ACLs) 17 18Support for UFS access control lists may be enabled by adding: 19 20 options UFS_ACL 21 22to your kernel configuration. As ACLs rely on the availability of extended 23attributes, your file systems must have support for extended attributes. 24For UFS2, this is supported natively, so no further configuration is 25necessary. For UFS1, you must also enable the optional extended attributes 26support documented in README.extattr. A summary of the instructions 27and ACL-specific information follows. 28 29To enable support for ACLs on a file system, the 'acls' mount flag 30must be set for the file system. This may be set using the tunefs 31'-a' flag: 32 33 tunefs -a enable /dev/md0a 34 35Or by using the mount-time flag: 36 37 mount -o acls /dev/md0a /mnt 38 39The flag may also be set in /etc/fstab. Note that mounting a file 40system previously configured for ACLs without ACL-support will result 41in incorrect application of discretionary protections. Likewise, 42mounting an ACL-enabled file system without kernel support for ACLs 43will result in incorrect application of discretionary protections. If 44the kernel is not configured for ACL support, a warning will be 45printed by the kernel at mount-time. For reliability purposes, it 46is recommended that the superblock flag be used instead of the 47mount-time flag, as this will avoid re-mount isses with the root file 48system. For reliability and performance reasons, the use of ACLs on 49UFS1 is discouraged; UFS2 extended attributes provide a more reliable 50storage mechanism for ACLs. 51 52Currently, support for ACLs on UFS1 requires the use of UFS1 EAs, which may 53be enabled by adding: 54 55 options UFS_EXTATTR 56 57to your kernel configuration file and rebuilding. Because of filesystem 58mount atomicity requirements, it is also recommended that: 59 60 options UFS_EXTATTR_AUTOSTART 61 62be added to the kernel so as to support the atomic enabling of the 63required extended attributes with the filesystem mount operation. To 64enable ACLs, two extended attributes must be available in the 65EXTATTR_NAMESPACE_SYSTEM namespace: "posix1e.acl_access", which holds 66the access ACL, and "posix1e.acl_default" which holds the default ACL 67for directories. If you're using UFS1 Extended Attributes, the following 68commands may be used to create the necessary EA backing files for 69ACLs in the filesystem root of each filesystem. In these examples, 70the root filesystem is used; see README.extattr for more details. 71 72 mkdir -p /.attribute/system 73 cd /.attribute/system 74 extattrctl initattr -p / 388 posix1e.acl_access 75 extattrctl initattr -p / 388 posix1e.acl_default 76 77On the next mount of the root filesystem, the attributes will be 78automatically started, and ACLs will be enabled. 79