utmp man page on 4.4BSD

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UTMP(5)			    BSD File Formats Manual		       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
     either 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 pro‐
     gram 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 charac‐
		 ter ‘~’ 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 ‘|’ indi‐
		 cates the time prior to the change, and the character ‘{’
		 indicates the new time.

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

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 lastlog
     file format appeared in 3.0BSD.

4th Berkeley Distribution	 June 1, 1994	     4th Berkeley Distribution
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