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

     utmp, wtmp, lastlog -- login records

     #include <sys/types.h>
     #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.

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

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

	   struct lastlog {
		   time_t  ll_time;		   /* When user	logged in */
		   char	   ll_line[UT_LINESIZE];   /* Terminal line name */
		   char	   ll_host[UT_HOSTSIZE];   /* Host user	came from */

	   struct utmp {
		   char	   ut_line[UT_LINESIZE];   /* Terminal line name */
		   char	   ut_name[UT_NAMESIZE];   /* User's login name	*/
		   char	   ut_host[UT_HOSTSIZE];   /* Host user	came from */
		   time_t  ut_time;		   /* When user	logged in */

     The lastlog file is a linear array	of lastlog structures indexed by a
     user's UID.  The utmp file	is a linear array of utmp structures indexed
     by	a terminal line	number (see ttyslot(3)).  The wtmp file	consists of
     utmp structures and is a binary log file, that is,	grows linearly at its

     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 (unless the login is 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 is 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(1)	program	opens the file wtmp, and appends the user's
     utmp record.  The user's subsequent logout	from the terminal line is
     marked by a special utmp record with ut_line set accordingly, ut_time up-
     dated, but	ut_name	and ut_host both empty (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.

     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 reboot(8)).

     date      The system time has been	manually or automatically updated (see
	       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.

     The wtmp file can grow rapidly on busy systems, so	daily or weekly	rota-
     tion is recommended.  It is maintained by newsyslog(8).

     If	any one	of these files does not	exist, it is not created by login(1).
     They must be created manually.

     The supplied login(3), logout(3), and logwtmp(3) utility functions	should
     be	used to	perform	the standard actions on	the utmp and wtmp files	in or-
     der to maintain the portability across systems with different formats of
     those files.

     /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), login(3),	logout(3), logwtmp(3),
     ttyslot(3), ac(8),	init(8)

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

BSD			       November	14, 2001			   BSD


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