ps(1): '-U' to select processes by real user IDs

This is what POSIX mandates for option '-U' and arguably the behavior
that most users actually need in most cases.  Before, '-U' would select
processes by their effective user IDs (which is the behavior mandated by
POSIX for option '-u').

Matching by real user IDs allows to list all processes belonging to the
passed users, including those temporarily having a different effective
user ID, which can happen if launched by a setuid executable or if using
some credentials-changing facility (such as seteuid() for root processes
or mac_do(4)/setcred(2)).  Conversely, processes temporarily assuming
the identity of some of the passed users will not be listed anymore
(they do not "belong" to these users).

This change also makes '-U' consistent with '-G', the latter already
matching on real group IDs.

While here, remove the (non-compiled) code for tentative option '-R' as
its proposed behavior was the one established here for '-U'.  Also, move
the compiled-out old code for '-U' under '-u' for reference, as this is
what the latter should do according to POSIX, even if it seems unlikely
we will want to change the behavior of '-u'.

Reviewed by:    manpages (ziaee)
MFC after:      3 days
Relnotes:       yes
Sponsored by:   The FreeBSD Foundation
Differential Revision:  https://reviews.freebsd.org/D49622 (code)
Differential Revision:  https://reviews.freebsd.org/D49623 (manual page)

2 files changed, 23 insertions, 28 deletions

diff --git a/bin/ps/ps.1 b/bin/ps/ps.1
index 174f18a2f2d9..ff9a847ffd86 100644
--- a/bin/ps/ps.1
+++ b/bin/ps/ps.1
@@ -371,8 +371,8 @@ Implies
 .Fl x
 by default.
 .It Fl U
-Display information about processes whose effective user ID matches the
-specified user IDs or names.
+Display information about processes whose real user ID matches the specified
+user IDs or names.
 Implies
 .Fl x
 by default.
@@ -953,20 +953,16 @@ equivalently to
 .Pc ,
 and option
 .Fl u
-to select processes by effective user ID
-.Po
-which is the current behavior of option
-.Fl U
-.Pc .
+to select processes by effective user ID.
 .Pp
 However, options
-.Fl A , a , G , l , o , p ,
+.Fl A , a , G , l , o , p , U ,
 and
 .Fl t
 behave as prescribed by
 .St -p1003.1-2024 .
 Options
-.Fl f , U ,
+.Fl f
 and
 .Fl w
 currently do not, but may be changed to in the future.
diff --git a/bin/ps/ps.c b/bin/ps/ps.c
index 6c007e8fc1a1..a75ea512ad54 100644
--- a/bin/ps/ps.c
+++ b/bin/ps/ps.c
@@ -356,20 +356,6 @@ main(int argc, char *argv[])
 			 */
 			nselectors++;
 			break;
-#if 0
-		case 'R':
-			/*
-			 * XXX - This un-standard option is still under
-			 *	debate.  This is what SUSv3 defines as
-			 *	the `-U' option, and while it would be
-			 *	nice to have, it could cause even more
-			 *	confusion to implement it as `-R'.
-			 */
-			add_list(&ruidlist, optarg);
-			xkeep_implied = 1;
-			nselectors++;
-			break;
-#endif
 		case 'r':
 			sortby = SORTCPU;
 			break;
@@ -401,21 +387,34 @@ main(int argc, char *argv[])
 			nselectors++;
 			break;
 		case 'U':
+			add_list(&ruidlist, optarg);
+			xkeep_implied = 1;
+			nselectors++;
+			break;
+		case 'u':
+#if 0
 			/*
-			 * POSIX says that '-U' should match on real user IDs,
-			 * not effective ones as we are doing here, which is
-			 * normally the behavior of option '-u' according to the
-			 * standard.
+			 * POSIX's '-u' behavior.
+			 *
+			 * This has not been activated because:
+			 * 1. Option '-U' is a substitute for most users, and
+			 *    those that care seem more likely to want to match
+			 *    on the real user ID to display all processes
+			 *    launched by some users.
+			 * 2. '-u' has been a canned display on the BSDs for
+			 *    a very long time (POLA).
 			 */
 			add_list(&uidlist, optarg);
 			xkeep_implied = 1;
 			nselectors++;
 			break;
-		case 'u':
+#else
+			/* Historical BSD's '-u'. */
 			parsefmt(ufmt, &varlist, 0);
 			sortby = SORTCPU;
 			_fmt = 1;
 			break;
+#endif
 		case 'v':
 			parsefmt(vfmt, &varlist, 0);
 			sortby = SORTMEM;