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UTMP(5)                       File Formats Manual                      UTMP(5)

     utmp, wtmp, lastlog - login records

     #include <utmp.h>

     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.

     The wtmp file can grow rapidly on busy systems, and is normally rotated
     with newsyslog(8).

     These files must be created manually; if they do not exist, they are not
     created automatically.

           #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];
                   time_t  ut_time;

     Each time a user logs in, the login(1) 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 set quiet; see login(1).  The
     login(1) 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 (by clearing the user and host
     fields, and updating the timestamp field).  The utmp file is used by the
     programs rwho(1), users(1), w(1), and who(1).

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

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

     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

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

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

     last(1), login(1), w(1), who(1), utmpx(5), ac(8), init(8), lastlogin(8),

     A utmp file format appeared in Version 1 AT&T UNIX.  The wtmp file format
     appeared in Version 2 AT&T UNIX.  The lastlog file format appeared in

NetBSD 10.99                   September 9, 2019                  NetBSD 10.99