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UTMP(5)			    BSD	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 charac-
		 ter `~' 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 and	wtmp file format appeared in Version 6 AT&T UNIX.  The lastlog
     file format appeared in 3.0BSD.

BSD				 May 14, 2003				   BSD


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