UTMP(5)                   OpenBSD Programmer's Manual                  UTMP(5)

NAME
     utmp, wtmp, lastlog - login records

SYNOPSIS
     #include <utmp.h>

DESCRIPTION
     The <utmp.h> file declares the structures used to record information
     about current users in the utmp file, logins and logouts in the wtmp
     file, and last logins in the lastlog file.  The timestamps of date
     changes, shutdowns, and reboots are also logged in the wtmp file.

     wtmp can grow rapidly on busy systems, so daily or weekly rotation is
     recommended.  If any one of these files does not exist, it is not creat-
     ed.  They must be created manually and are maintained by newsyslog(8).

           #define _PATH_UTMP      "/var/run/utmp"
           #define _PATH_WTMP      "/var/log/wtmp"
           #define _PATH_LASTLOG   "/var/log/lastlog"

           #define UT_NAMESIZE     32
           #define UT_LINESIZE     8
           #define UT_HOSTSIZE     256

           struct lastlog {
                   time_t  ll_time;
                   char    ll_line[UT_LINESIZE];
                   char    ll_host[UT_HOSTSIZE];
           };

           struct utmp {
                   char    ut_line[UT_LINESIZE];
                   char    ut_name[UT_NAMESIZE];
                   char    ut_host[UT_HOSTSIZE];
                   time_t  ut_time;
           };

     Each time a user logs in, the login(1) program looks up the user's UID in
     the lastlog file.  If it is found, the timestamp of the last time the us-
     er logged in, the terminal line, and the hostname are written to the
     standard output (provided the login is not ``quiet''; see login(1)).  The
     login(1) program then records the new login time in the lastlog file.

     After the new lastlog record is written, the utmp file is opened and the
     utmp record for the user is inserted.  This record remains until the user
     logs out at which time it is deleted.  The utmp file is used by the pro-
     grams rwho(1), users(1), w(1), and who(1).

     Next, the login(1) program opens the wtmp file and appends the user's
     utmp record.  When the user logs out, a utmp record with the tty line, an
     updated timestamp, and zeroed name and host fields is appended to the
     file (see init(8)).  The wtmp file is used by the programs last(1) and
     ac(8).

     In the event of a date change, shutdown, or reboot, the following items
     are logged in the wtmp file:

     reboot
     shutdown    A system reboot or shutdown has been initiated.  A tilde
                 (`~') character is placed in the field ut_line, and
                 ``reboot'' or ``shutdown'' in the field ut_name (see
                 shutdown(8) and reboot(8)).

     date        The system time has been manually or automatically updated
                 (see date(1)).  The command name date(1) is recorded in the
                 field ut_name.  In the field ut_line, the ``|'' character in-
                 dicates the time prior to the change and the ``{'' character
                 indicates the new time.

FILES
     /var/run/utmp
     /var/log/wtmp
     /var/log/lastlog

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

HISTORY
     A utmp and wtmp file format appeared in Version 3 AT&T UNIX.  The lastlog
     file format appeared in 3.0BSD.

CAVEATS
     The strings in the utmp and lastlog structures are not normal `C' strings
     and are thus not guaranteed to be null terminated.

OpenBSD 4.7                      May 31, 2007                                2
