NAME

       acl — virtual file system access control lists

SYNOPSIS

       #include <sys/param.h>
       #include <sys/vnode.h>
       #include <sys/acl.h>

       In the kernel configuration file:
       options UFS_ACL

DESCRIPTION

       Access  control  lists, or ACLs, allow fine-grained specification of rights for vnodes representing files
       and directories.  However, as there are a plethora of file systems  with  differing  ACL  semantics,  the
       vnode  interface  is aware only of the syntax of ACLs, relying on the underlying file system to implement
       the details.  Depending on the underlying file system, each file or directory may have zero or more  ACLs
       associated  with  it,  named  using  the  type field of the appropriate vnode ACL calls: VOP_ACLCHECK(9),
       VOP_GETACL(9), and VOP_SETACL(9).

       Currently, each ACL is represented in-kernel by a fixed-size acl structure, defined as follows:

             struct acl {
                     unsigned int            acl_maxcnt;
                     unsigned int            acl_cnt;
                     int                     acl_spare[4];
                     struct acl_entry        acl_entry[ACL_MAX_ENTRIES];
             };

       An ACL is constructed from a fixed size array of ACL  entries,  each  of  which  consists  of  a  set  of
       permissions, principal namespace, and principal identifier.  In this implementation, the acl_maxcnt field
       is always set to ACL_MAX_ENTRIES.

       Each individual ACL entry is of the type acl_entry_t, which is a structure with the following members:

       acl_tag_t ae_tag
           The following is a list of definitions of ACL types to be set in ae_tag:

                 ACL_UNDEFINED_FIELD  Undefined ACL type.
                 ACL_USER_OBJ         Discretionary  access rights for processes whose effective user ID matches
                                      the user ID of the file's owner.
                 ACL_USER             Discretionary access rights for processes whose effective user ID  matches
                                      the ACL entry qualifier.
                 ACL_GROUP_OBJ        Discretionary  access rights for processes whose effective group ID or any
                                      supplemental groups match the group ID of the file's owner.
                 ACL_GROUP            Discretionary access rights for processes whose effective group ID or  any
                                      supplemental groups match the ACL entry qualifier.
                 ACL_MASK             The  maximum  discretionary access rights that can be granted to a process
                                      in the file group class.  This is only valid for POSIX.1e ACLs.
                 ACL_OTHER            Discretionary access rights for processes not covered  by  any  other  ACL
                                      entry.  This is only valid for POSIX.1e ACLs.
                 ACL_OTHER_OBJ        Same as ACL_OTHER.
                 ACL_EVERYONE         Discretionary  access  rights for all users.  This is only valid for NFSv4
                                      ACLs.

           Each POSIX.1e ACL must contain exactly one ACL_USER_OBJ, one ACL_GROUP_OBJ, and  one  ACL_OTHER.   If
           any  of  ACL_USER,  ACL_GROUP,  or  ACL_OTHER  are present, then exactly one ACL_MASK entry should be
           present.

       uid_t ae_id
           The ID of user for whom this ACL describes access permissions.  For entries other than  ACL_USER  and
           ACL_GROUP, this field should be set to ACL_UNDEFINED_ID.

       acl_perm_t ae_perm
           This field defines what kind of access the process matching this ACL has for accessing the associated
           file.  For POSIX.1e ACLs, the following are valid:

           ACL_EXECUTE            The process may execute the associated file.

           ACL_WRITE              The process may write to the associated file.

           ACL_READ               The process may read from the associated file.

           ACL_PERM_NONE          The process has no read, write or execute permissions to the associated file.

           For NFSv4 ACLs, the following are valid:

           ACL_READ_DATA          The process may read from the associated file.

           ACL_LIST_DIRECTORY     Same as ACL_READ_DATA.

           ACL_WRITE_DATA         The process may write to the associated file.

           ACL_ADD_FILE           Same as ACL_ACL_WRITE_DATA.

           ACL_APPEND_DATA

           ACL_ADD_SUBDIRECTORY   Same as ACL_APPEND_DATA.

           ACL_READ_NAMED_ATTRS   Ignored.

           ACL_WRITE_NAMED_ATTRS  Ignored.

           ACL_EXECUTE            The process may execute the associated file.

           ACL_DELETE_CHILD

           ACL_READ_ATTRIBUTES

           ACL_WRITE_ATTRIBUTES

           ACL_DELETE

           ACL_READ_ACL

           ACL_WRITE_ACL

           ACL_WRITE_OWNER

           ACL_SYNCHRONIZE        Ignored.

       acl_entry_type_t ae_entry_type
           This  field  defines  the type of NFSv4 ACL entry.  It is not used with POSIX.1e ACLs.  The following
           values are valid:

           ACL_ENTRY_TYPE_ALLOW

           ACL_ENTRY_TYPE_DENY

       acl_flag_t ae_flags
           This field defines the inheritance flags of NFSv4 ACL entry.  It is not used with POSIX.1e ACLs.  The
           following values are valid:

           ACL_ENTRY_FILE_INHERIT

           ACL_ENTRY_DIRECTORY_INHERIT

           ACL_ENTRY_NO_PROPAGATE_INHERIT

           ACL_ENTRY_INHERIT_ONLY

SEE ALSO

       acl(3), vaccess_acl_nfs4(9), vaccess_acl_posix1e(9), VFS(9), vaccess(9), VOP_ACLCHECK(9),  VOP_GETACL(9),
       VOP_SETACL(9)

AUTHORS

       This manual page was written by Robert Watson.

Debian                                         September 18, 2009                                         ACL(9)