9 Jan
2015
9 Jan
'15
7:06 p.m.
From: Noel Chiappa
For some reason, the code for /etc/init .. bashes the
command line so
it just has '-' in it, so it looks just like a shell.
BTW, that may be accidental, not a deliberate choice - e.g. someone copied
another line of code which exec'd a shell, and didn't change the second arg.
I fixed my copy so it says "/etc/init", or
something like that. ... I
can upload the 'fixed' code tomorrow.
The change is pretty minor: in this piece of code:
case reboot:
termall();
execl(init, minus, 0);
reset();
just change the execl() line to say:
execl(init, init, 0);
> I'm not sure if unix of the v6 or v5 era was
designed to go from multi
> user to single user mode and then back again.
I seem to recall there's some issue, something
like in some cases
there's an extra shell left running attached to the console
So the bug is that in going from single-user to multi-user, by using "kill -1
1" in single-user with the switch register set for multi-user, it doesn't
kill the running single-user shell on the console. The workaround to that bug
which I use is to set the CSWR and then ^D the running shell.
In general, the code in init.c isn't quite as clean/clear as would be optimal
(which is part of why I haven't tried to fix the above bug), but _in general_
it does support going back and forth.
From: Ronald Natalie
our init checked the switch register to determine
whether to bring up
single or multiuser
I think that's standard from Bell, actually.
I believe our system shutdown if you kill -1-1 (HUP to
init).
The 'stock' behaviour is that when that happens, it checks the switch
register, and there are three options (the code is a little hard to follow,
but I'm pretty sure this is right):
- if it's set for single-user, it shuts down all the other children, and
brings up a console shell; when done, it does the next
- if it's set for 'reboot', it just shuts down all children, and restarts
the init process (presumably so one can switch to a new version of the init
without restarting the whole machine);
- if it's not set for either, it re-reads /etc/ttys, and for any lines which
have switched state in that file, it starts/kills the process listening to
that line (this allows one to add/drop lines dynamically).
From: Clem Cole
it's probably worth digging up the v6 version of
fsck.
That's on that MIT V6 tape, too. Speaking of which, time to write the code to
grok the tape...
Noel