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NetBSD 6.1.5 - man page for utmp (netbsd section 5)

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 automati-

	   #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 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 by date(1).  The com-
		 mand 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), newsyslog(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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