UTMP(5)                     BSD File Formats Manual                    UTMP(5)

NAME
     utmp, wtmp, lastlog -- login records

SYNOPSIS
     ##include <>

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

     These files can grow rapidly on busy systems, daily or weekly rotation is
     recommended.  If any of these files do not exist, it is not created.
     These files must be created manually and are normally maintained in
     either the script /etc/daily or the script /etc/weekly.  (See cron(8).)

           #define PATHUTMP      "/var/run/utmp"
           #define PATHWTMP      "/var/log/wtmp"
           #define PATHLASTLOG   "/var/log/lastlog"

           #define UTNAMESIZE     8
           #define UTLINESIZE     8
           #define UTHOSTSIZE     16

           struct lastlog {
                   timet  lltime;
                   char    llline[UTLINESIZE];
                   char    llhost[UTHOSTSIZE];
           };

           struct utmp {
                   char    utline[UTLINESIZE];
                   char    utname[UTNAMESIZE];
                   char    uthost[UTHOSTSIZE];
                   timet  uttime;
           };

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

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

     Next, the login program opens the file wtmp, and appends the user's utmp
     record.  The same utmp record, with an updated time stamp is later
     appended to the file when the user logs out. (See init(8).)  The wtmp
     file is used by the programs last(1) and ac(8).

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

     reboot
     shutdown    A system reboot or shutdown has been initiated.  The charac-
                 ter `~' is placed in the field utline, and reboot or
                 shutdown in the field utname.  (See shutdown(8) and
                 reboot(8).)

     date        The system time has been manually or automatically updated.
                 (See date(1).)  The command name date is recorded in the
                 field utname.  In the field utline, the character `' indi-
                 cates the time prior to the change, and the character `{'
                 indicates the new time.

FILES
     /var/run/utmp     The utmp file.
     /var/log/wtmp     The wtmp file.
     /var/log/lastlog  The lastlog file.

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

HISTORY
     A utmp and wtmp file format appeared in Version 6 AT&T UNIX.  The lastlog
     file format appeared in 3.0BSD.

4th Berkeley Distribution       March 17, 1994       4th Berkeley Distribution