wtmp man page on FreeBSD

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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 {
		   int32_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 */
		   int32_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

     By default, each time a user logs in, the pam_lastlog(8) 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.  The pam_lastlog(8) 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 pam_lastlog(8) 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
     updated, 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
     pam_lastlog(8).  The files 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
     order 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), w(1), who(1), login(3), logout(3), logwtmp(3), ttyslot(3),
     ac(8), init(8), pam_lastlog(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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