man(1) Manual page archive

     UTMP(5)                                                   UTMP(5)

          utmp, wtmp - login records

          #include <utmp.h>

          The utmp file allows one to discover information about who
          is currently logged in.  The file is a sequence of entries
          with the following structure declared in the include file:

               struct utmp {
                    char ut_line[8];  /* tty name */
                    char ut_name[8];  /* user id */
                    long ut_time;     /* time on */

          This structure gives the name of the special file associated
          with the user's terminal, the user's login name, and the
          time of the login in the form of time(2).

          The wtmp file records logins and logouts.  Its format is
          exactly like utmp except that a null user name indicates a
          logout on the associated terminal.  Furthermore, the termi-
          nal name `~' indicates that the system was rebooted at the
          indicated time; the adjacent pair of entries with terminal
          names `|' and `}' indicate the system-maintained time just
          before and just after a date(1) command changed the system's
          idea of the time.

          Wtmp is maintained by login(8) and init(8). Neither of these
          programs creates the file, so if it is removed record-
          keeping is turned off.  It is summarized by ac(8).

          login(8), init(8), who(1), ac(8)