Added comments to macros for ut_type field.

man5/utmp.5

@@ -55,16 +55,20 @@ around; details depend on the version of libc):
 .sp
 /* Values for ut_type field, below */
 
-#define UT_UNKNOWN      0
-#define RUN_LVL         1
-#define BOOT_TIME       2
-#define NEW_TIME        3
-#define OLD_TIME        4
-#define INIT_PROCESS    5
-#define LOGIN_PROCESS   6
-#define USER_PROCESS    7
-#define DEAD_PROCESS    8
-#define ACCOUNTING      9
+#define EMPTY         0  /* Record does not contain valid info
+                            (formerly known as UT_UNKNOWN) */
+#define RUN_LVL       1  /* Change in system run-level (see
+                            \fBinit\fP(8) */
+#define BOOT_TIME     2  /* Time of system booy (in \fIut_tv\fP) */
+#define NEW_TIME      3  /* Time after system clock change
+                            (in \fIut_tv\fP) */
+#define OLD_TIME      4  /* Time before system clock change
+                            (in \fIut_tv\fP) */
+#define INIT_PROCESS  5  /* Process spawned by \fBinit\fP(8) */
+#define LOGIN_PROCESS 6  /* Session leader process for user login */
+#define USER_PROCESS  7  /* Normal process */
+#define DEAD_PROCESS  8  /* Terminated process */
+#define ACCOUNTING    9  /* Not implemented */
 
 #define UT_LINESIZE      32
 #define UT_NAMESIZE      32