UTMP(5)                          File Formats                          UTMP(5)

NAME

       utmp, wtmp, lastlog - login records

SYNOPSIS

       #include <utmp.h>

DESCRIPTION

       The  file  <utmp.h>  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 ei‐
       ther the script /etc/daily or the script /etc/weekly.  (See cron(8).)

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

       #define UT_NAMESIZE     8
       #define UT_LINESIZE     8
       #define UT_HOSTSIZE     16

       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];
               long    ut_time;
       };

       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 program 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
                     character ~ is placed in the field ut_line, and reboot or
                     shutdown in the field ut_name.  (See shutdown(8) and  re����
                     boot(8).)

              date   The  system  time  has been manually or automatically up‐
                     dated.  (See date(1).)  The command name date is recorded
                     in  the field ut_name.  In the field ut_line, the charac‐
                     ter  indicates the time prior  to  the  change,  and  the
                     character { indicates the new time.

FILES

              /var/run/utmp
                     The utmpfile.

              /var/log/wtmp
                     The wtmpfile.

              /var/log/lastlog
                     The lastlogfile.

BUGS

       This man page is not quite right for the GNO implementation (the struc‐
       tures are incorrect, as is the utmp path).

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 last����
       log file format appeared in 3.0BSD.



GNO                            17 September 1997                       UTMP(5)