2.11BSD#431 - /usr/man/cat8/init.0

INIT(8)             UNIX Programmer's Manual		  INIT(8)


NAME
     init - process control initialization

SYNOPSIS
     /etc/init

DESCRIPTION
     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 com-
     mences 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 hit-
     ting ^D), init runs /etc/rc without the reboot parameter.
     This command file performs housekeeping operations such as
     removing temporary files, mounting file systems, and start-
     ing daemons.

     In multi-user operation, init's 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 specified in the file.  This com-
     mand will usually be /usr/libexec/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 the wtmp, file 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 appropri-
     ate terminal is reopened and getty is reinvoked.

     Init catches the hangup signal (signal SIGHUP) and inter-
     prets 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 pro-
     cess: use `kill -HUP 1.'

     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


Printed 11/24/99	November 27, 1996			1


INIT(8)             UNIX Programmer's Manual		  INIT(8)


     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 warn-
     ing message.

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

     Init's 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.

DIAGNOSTICS
     /usr/libexec/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,

     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.

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

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


Printed 11/24/99	November 27, 1996			2