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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 {
                   int                     acl_cnt;
                   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.

     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.
               ACL_OTHER            Discretionary access rights for processes
                                    not covered by any other ACL entry.
               ACL_OTHER_OBJ        Same as ACL_OTHER.  Each ACL entry 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.

     acl_perm_t ae_perm
         This field defines what kind of access the process matching this ACL
         has for accessing the associated file.

         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.

IMPLEMENTATION NOTES

     typedef mode_t  *acl_permset_t;

     /* internal ACL structure */
     struct acl {
             int                     acl_cnt;
             struct acl_entry        acl_entry[ACL_MAX_ENTRIES];
     };

     /* external ACL structure */
     struct acl_t_struct {
             struct acl              ats_acl;
             int                     ats_cur_entry;
     };
     typedef struct acl_t_struct *acl_t;

     /*
      * Possible valid values for ae_tag field.
      */
     #define ACL_UNDEFINED_TAG       0x00000000
     #define ACL_USER_OBJ            0x00000001
     #define ACL_USER                0x00000002
     #define ACL_GROUP_OBJ           0x00000004
     #define ACL_GROUP               0x00000008
     #define ACL_MASK                0x00000010
     #define ACL_OTHER               0x00000020
     #define ACL_OTHER_OBJ           ACL_OTHER

     /*
      * Possible valid values for acl_type_t arguments.
      */
     #define ACL_TYPE_ACCESS         0x00000000
     #define ACL_TYPE_DEFAULT        0x00000001
     #define ACL_TYPE_AFS            0x00000002
     #define ACL_TYPE_CODA           0x00000003
     #define ACL_TYPE_NTFS           0x00000004
     #define ACL_TYPE_NWFS           0x00000005

     /*
      * Possible flags in ae_perm field.
      */
     #define ACL_EXECUTE             0x0001
     #define ACL_WRITE               0x0002
     #define ACL_READ                0x0004
     #define ACL_PERM_NONE           0x0000
     #define ACL_PERM_BITS           (ACL_EXECUTE | ACL_WRITE | ACL_READ)
     #define ACL_POSIX1E_BITS        (ACL_EXECUTE | ACL_WRITE | ACL_READ)

     /*
      * Possible entry_id values for acl_get_entry()
      */
     #define ACL_FIRST_ENTRY         0
     #define ACL_NEXT_ENTRY          1

     /*
      * Undefined value in ae_id field
      */
     #define ACL_UNDEFINED_ID        ((uid_t)-1)

SEE ALSO

     acl(3), vaccess_acl_posix1e(9), VFS(9), vnaccess(9), VOP_ACLCHECK(9),
     VOP_GETACL(9), VOP_SETACL(9)

AUTHORS

     This manual page was written by Robert Watson.