INIT(8)                                                                INIT(8)

       init - process control initialization


       Init is invoked inside UNIX as the last step in the boot procedure.  It
       normally then runs  the  automatic  reboot  sequence  as  described  in
       reboot(8),  and  if this succeeds, begins multi-user operation.  If the
       reboot fails, it commences single user operation by giving  the  super-
       user  a  shell  on the console.  It is possible to pass parameters from
       the boot program to init so that single  user  operation  is  commenced
       immediately.   When such single user operation is terminated by killing
       the single-user shell (i.e. by hitting ^D), init runs  /etc/rc  without
       the  reboot  parameter.  This command file performs housekeeping opera‐
       tions such as removing temporary  files,  mounting  file  systems,  and
       starting daemons.

       In  multi-user  operation,  inits role is to create a process for each
       terminal port on which a user may log in.  To begin such operations, it
       reads the file /etc/ttys and executes a command for each terminal spec‐
       ified in the file.  This command will  usually  be  /etc/getty.   Getty
       opens  and  initializes  the  terminal  line, reads the user’s name and
       invokes login to log in the user and execute the Shell.

       Ultimately the Shell will terminate because of  an  end-of-file  either
       typed explicitly or generated as a result of hanging up.  The main path
       of init, which has been waiting for such an event, wakes up and removes
       the  appropriate entry from the file utmp, which records current users,
       and makes an entry in  /usr/adm/wtmp,  which  maintains  a  history  of
       logins  and  logouts.   The wtmp entry is made only if a user logged in
       successfully on the line.  Then the appropriate  terminal  is  reopened
       and getty is reinvoked.

       Init  catches  the  hangup  signal (signal SIGHUP) and interprets it to
       mean that the file /etc/ttys should be read again.  The  Shell  process
       on  each line which used to be active in ttys but is no longer there is
       terminated; a new  process  is  created  for  each  added  line;  lines
       unchanged  in the file are undisturbed.  Thus it is possible to drop or
       add terminal lines without rebooting the system by  changing  the  ttys
       file  and  sending  a hangup signal to the init process: use ‘kill -HUP

       Init will terminate multi-user operations and resume  single-user  mode
       if sent a terminate (TERM) signal, i.e. ‘‘kill -TERM 1’’.  If there are
       processes outstanding which are deadlocked (due to hardware or software
       failure), init will not wait for them all to die (which might take for‐
       ever), but will time out after 30 seconds and print a warning  message.

       Init will cease creating new getty’s and allow the system to slowly die
       away, if it is sent a terminal stop (TSTP) signal,  i.e.  ‘‘kill  -TSTP
       1’’.   A later hangup will resume full multi-user operations, or a ter‐
       minate will initiate a  single  user  shell.   This  hook  is  used  by
       reboot(8) and halt(8).

       Inits  role  is  so  critical  that if it dies, the system will reboot
       itself automatically.  If, at bootstrap time, the init  process  cannot
       be located, the system will loop in user mode at location 0x13.

       /etc/getty  gettyargs  failing,  sleeping.   A process being started to
       service a line is exiting quickly each time it  is  started.   This  is
       often  caused by a ringing or noisy terminal line.  Init will sleep for
       30 seconds, then continue trying to start the process.

       WARNING: Something is hung (wont die); ps axl advised.   A  process  is
       hung  and  could not be killed when the system was shutting down.  This
       is usually caused by a process which is stuck in a device driver due to
       a persistent device error condition.

       /dev/console, /dev/tty*, /etc/utmp, /usr/adm/wtmp, /etc/ttys, /etc/rc

       login(1),   kill(1),   sh(1),   ttys(5),  crash(8V),  getty(8),  rc(8),
       reboot(8), halt(8), shutdown(8)

4th Berkeley Distribution        May 22, 1986                          INIT(8)
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