V3/usr/man/man7/init.7

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NAME		init  --  process control initialization
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SYNOPSIS	/etc/init
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DESCRIPTION
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init____
is invoked inside UNIX as the last step in the boot procedure.
Generally its role is to create a process for each
typewriter on which a user may log in.

First, init____ checks
to see if the console switches contain 173030.
(This number is likely to vary between
systems.)
If so, the console typewriter tty___ is opened for reading
and writing and the shell is invoked immediately.
This feature is used to bring up a test system, or one
which does not contain DC-11 communications interfaces.
When the system is brought up in this way, the getty_____
and login_____ routines mentioned below and described elsewhere are not needed.

Otherwise, init____ does some housekeeping: the mode of
each DECtape file is changed to 17 (in case the system
crashed during a tap___ command);
directory /usr is mounted
on the RK0 disk;
directory /sys is mounted on the RK1 disk.
Also a data-phone daemon
is spawned to restart any jobs being sent.

Then init____ forks several times to create a process
for each typewriter mentioned in an internal table.
Each of these processes opens the appropriate typewriter
for reading and writing.  These channels thus
receive file descriptors 0 and 1, the standard input and
output.
Opening the typewriter will usually involve a delay,
since the open____ is not completed until someone
is dialled in (and carrier established) on the channel.
Then the process executes the program /etc___/getty_____
(q.v.).
getty_____ will read the user's name and invoke login_____ (q.v.)
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 wtmp____, which maintains a history
of logins and logouts.
Then the appropriate typewriter is reopened and getty_____
reinvoked.
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FILES		/dev/tap?,
/dev/tty, /dev/tty?, /tmp/utmp, /tmp/wtmp
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SEE ALSO	login(I), login(VII), getty(VII), sh(I), dpd(VII)
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DIAGNOSTICS	none possible
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BUGS		none possible