Figure 1: utmp record structure as defined in utmp.h

struct utmp {
char ut_user[8];          /* User login name */
char ut_line[12];         /* Device name */
short ut_pid;             /* Process id */
short ut_type;            /* Type of entry */
struct exit_status {
short e_termination;     /* Process termination status */
short e_exit;            /* Process exit status */
} ut_exit;
time_t ut_time;           /* Time entry was made */
stnet termio ut_termio;   /* Saved login termio parameters */
};