UTMP(5) File formats UTMP(5)
NAME
utmp, wtmp - login records
SYNOPSIS
#include <utmp.h>
DESCRIPTION
The utmp file allows one to discover information about who is currently using the system. There may be more users currently using the sys-
tem, because not all programs use utmp logging.
Warning: utmp must not be writable, because many system programs (foolishly) depend on its integrity. You risk faked system logfiles and
modifications of system files if you leave utmp writable to any user.
The file is a sequence of entries with the following structure declared in the include file (note that this is only one of several defini-
tions around; details depend on the version of libc):
#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 UT_LINESIZE 12
#define UT_NAMESIZE 32
#define UT_HOSTSIZE 256
struct exit_status {
short int e_termination; /* process termination status. */
short int e_exit; /* process exit status. */
};
struct utmp {
short ut_type; /* type of login */
pid_t ut_pid; /* pid of login process */
char ut_line[UT_LINESIZE]; /* device name of tty - "/dev/" */
char ut_id[4]; /* init id or abbrev. ttyname */
char ut_user[UT_NAMESIZE]; /* user name */
char ut_host[UT_HOSTSIZE]; /* hostname for remote login */
struct exit_status ut_exit; /* The exit status of a process
marked as DEAD_PROCESS. */
long ut_session; /* session ID, used for windowing*/
struct timeval ut_tv; /* time entry was made. */
int32_t ut_addr_v6[4]; /* IP address of remote host. */
char pad[20]; /* Reserved for future use. */
};
/* Backwards compatibility hacks. */
#define ut_name ut_user
#ifndef _NO_UT_TIME
#define ut_time ut_tv.tv_sec
#endif
#define ut_xtime ut_tv.tv_sec
#define ut_addr ut_addr_v6[0]
This structure gives the name of the special file associated with the user's terminal, the user's login name, and the time of login in the
form of time(2). String fields are terminated by '