.TH UTMP 5
.SH NAME
utmp, wtmp \- logged in users, login and logout history
.SH SYNOPSIS
.nf
.ft B
#include <sys/types.h>
#include <utmp.h>
.SH DESCRIPTION
.de SP
.if t .sp 0.4
.if n .sp
..
The files
.B /etc/utmp
and
.B /usr/adm/wtmp
respectively contain the currently logged in users, and the history of
logins and logouts.
.PP
Each file is an array of the following structure defined in <utmp.h>:
.PP
.nf
.ta +5n +15n +15n
struct utmp {
	char	ut_user[8];	/* user name */
	char	ut_line[12];	/* terminal name */
	char	ut_host[16];	/* host name, when remote */
	time_t	ut_time;	/* login/logout time */
};
.SP
.ta +15n
#define ut_name ut_user	/* for compatibility with other systems */
.fi
.DT
.PP
The structure contains more fields than those listed, but they are only of
interest to
.B init
and
.BR login .
Note that the
.B ut_name
field is a compatibility alias for
.BR ut_user ,
it is actually better to use it.
.PP
A login entry is completely specified.  A logout entry has a null string for
.BR ut_name .
A shutdown or reboot entry has an
.B ut_line
field containing a "~" (tilde).  The
.B ut_name
field is usually the name of the program that did the shutdown, or "reboot"
at reboot.  This is a bit confusing, but note that there should always be
two such entries.  If you see just one entry then the system has crashed, if
you see two entries then the system was properly shut down and later
rebooted.
.SH FILES
.TP 25n
.B /etc/utmp
Currently logged in users.
.TP
.B /usr/adm/wtmp
History of logins and logouts.
.SH "SEE ALSO"
.BR who (1),
.BR ttyslot (3).
.SH AUTHOR
Kees J. Bot (kjb@cs.vu.nl)