#define UT_UNKNOWN 0


#define RUN_LVL  1


#define BOOT_TIME 2


#define NEW_TIME 3


#define OLD_TIME 4


#define INIT_PROCESS 5


#define LOGIN_PROCESS 6


#define USER_PROCESS 7


#define DEAD_PROCESS 8


#define ACCOUNTING 9





#define UT_LINESIZE 12


#define UT_NAMESIZE 32


#define UT_HOSTSIZE 256





struct exit_status {


  short int e_termination; /* process termination status.  */


  short int e_exit; /* process exit status.  */


};





struct utmp {


  short ut_type; /* type of login */


  pid_t ut_pid; /* pid of login process */


  char ut_line[UT_LINESIZE]; /* device name of tty - "/dev/" */


  char ut_id[4]; /* init id or abbrev. ttyname */


  char ut_user[UT_NAMESIZE]; /* user name */


  char ut_host[UT_HOSTSIZE]; /* hostname for remote login */


  struct exit_status ut_exit; /* The exit status of a process


    marked as DEAD_PROCESS. */


  long ut_session; /* session ID, used for windowing*/


  struct timeval ut_tv; /* time entry was made.  */


  int32_t ut_addr_v6[4]; /* IP address of remote host.  */


  char __unused[20]; /* Reserved for future use.  */


};





/* Backwards compatibility hacks.  */


#define ut_name ut_user


#ifndef _NO_UT_TIME


#define ut_time ut_tv.tv_sec


#endif


#define ut_xtime ut_tv.tv_sec


#define ut_addr ut_addr_v6[0]




  This structure gives the name of the special file associated with the


user's terminal, the user's login name, and the time of login in the form


of


  time(2) .

 String fields are terminated by '\0' if they are shorter than the size


of the field.


 

  


 The first entries ever created result from


  init(8) 

 processing


  inittab(5) .

 Before an entry is processed, though,


  init(8) 

 cleans up utmp by setting ut_type to DEAD_PROCESS, clearing


ut_user, ut_host, and ut_time with null bytes for each


record which ut_type is not DEAD_PROCESS or RUN_LVL


and where no process with PID ut_pid exists.  If no empty record


with the needed ut_id can be found, init creates a new one.  It


sets ut_id from the inittab, ut_pid and ut_time to the


current values, and ut_type to INIT_PROCESS.


 

  


   getty(8) 

 locates the entry by the pid, changes ut_type to


LOGIN_PROCESS, changes ut_time, sets ut_line, and waits


for connection to be established.


  login(8) ,

 after a user has been


authenticated, changes ut_type to USER_PROCESS, changes


ut_time, and sets ut_host and ut_addr.  Depending on


  getty(8) 

 and


  login(8) ,

 records may be located by


ut_line instead of the preferable ut_pid.


 

  


 When


  init(8) 

 finds that a process has exited, it locates its utmp


entry by ut_pid, sets ut_type to DEAD_PROCESS, and


clears ut_user, ut_host and ut_time with null bytes.


 

  


   xterm(1) 

 and other terminal emulators directly create a


USER_PROCESS record and generate the ut_id by using the last


two letters of /dev/ttyp%c or by using p%d for


/dev/pts/%d.  If they find a DEAD_PROCESS for this id,


they recycle it, otherwise they create a new entry.  If they can, they


will mark it as DEAD_PROCESS on exiting and it is advised that


they null ut_line, ut_time, ut_user, and ut_host


as well.


 

  


 xdm(8)  should not create a utmp record, because there is no


assigned terminal.  Letting it create one will result in errors, such


as 'finger: cannot stat /dev/machine.dom'.  It should create wtmp entries,


though, just like


  ftpd(8) 

 does.


 

  


   telnetd(8) 

 sets up a LOGIN_PROCESS entry and leaves the rest to


  login(8) 

 as usual.  After the telnet session ends,


  telnetd(8) 

 cleans up utmp in the described way.


 

  


 The wtmp file records all logins and logouts.  Its format is


exactly like utmp except that a null user name indicates a logout


on the associated terminal.  Furthermore, the terminal name ~


with user name shutdown or reboot indicates a system


shutdown or reboot and the pair of terminal names |/}


logs the old/new system time when


  date(1) 

 changes it.  wtmp is maintained by


  login(1) ,

   init(1) ,

 and some versions of


  getty(1) .

 Neither of these programs creates the file, so if it is


removed, record-keeping is turned off.