NAME
utmp, wtmp - login records

SYNOPSIS
#include <utmp.h>

DESCRIPTION
The utmp file records information about who is currently using the
system. The file is a sequence of entries with the following
structure declared in the include file:

/*
* Structure of utmp and wtmp files.
*
* Assuming the number 8 is unwise.
*/
struct utmp {
char ut_line[8]; /* tty name */
char ut_name[8]; /* user id */
char ut_host[16]; /* host name, if remote */
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(3).

The wtmp file records all logins and logouts. A null user name
indicates a logout on the associated terminal. Furthermore, the
terminal 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 command has changed the system’s idea of the
time.

Wtmp is maintained by login(1) and init(8). Neither of these
programs creates the file, so if it is removed record-keeping is
turned off.

FILES
/etc/utmp
/usr/adm/wtmp

SEE ALSO
last(1), login(1), who(1), init(8)