9 Jan
2015
9 Jan
'15
6:18 a.m.
From: Mark Longridge <cubexyz(a)gmail.com>
I've finally managed to get Unix v5 and v6 to go
into single user mode
while running under simh.
...
dep system sr 173030 (simh command)
Just out of curiousity, why don't you set the SR before you boot the machine?
That way it'll come up single user, and you can icheck/dcheck before you go
to multi-user mode. I prefer doing it that way, there's as little as possible
going on, in case the disk is slightly 'confused', so less chance any bit-rot
will spread...
Now I'm in muti user mode .. but then if I do a
"ps -alx" I get:
TTY F S UID PID PRI ADDR SZ WCHAN COMMAND
?: 3 S 0 0-100 1227 2 5676 ????
?: 1 W 0 1 40 1324 6 5740 -
The ps command doesn't show the /etc/init process
explicitly, although
I'm pretty sure it is running.
No, it's there: the second line (PID 1). For some reason, the code for
/etc/init (in V6 at least, I don't know anything about V5) bashes the command
line so it just has '-' in it, so it looks just like a shell.
I fixed my copy so it says "/etc/init", or something like that. The machine
my source is on is powered down at the moment; if you want, I can upload the
'fixed' code tomorrow.
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, but I don't recall the
details (too lazy to look for the note I made about the bug; I can look it up
if you really want to know).
Would it be safer to just go to single user and then
shut it down?
I don't usually bother; I just log out all the shells except the one on the
console, so the machine is basically idle; then do a 'sync', and shortly
after than completes, I just halt the machine.
Noel
9 Jan
9 Jan
2:23 p.m.
New subject: single user mode in v5 & v6
If I recall, our V6 system would go from singe user to multiuser when you logged out of
the single user shell (our init checked the switch register to determine whether to bring
up single or multiuser). I believe our system shutdown if you kill -1-1 (HUP to init).
V7 would revert to single user at that point.
I think the init
On Jan 9, 2015, at 1:18 AM, Noel Chiappa
<jnc(a)mercury.lcs.mit.edu> wrote:
From: Mark Longridge <cubexyz(a)gmail.com>
I've finally managed to get Unix v5 and v6
to go into single user mode
while running under simh.
...
dep system sr 173030 (simh command)
Just out of curiousity, why don't you set the SR before you boot the machine?
That way it'll come up single user, and you can icheck/dcheck before you go
to multi-user mode. I prefer doing it that way, there's as little as possible
going on, in case the disk is slightly 'confused', so less chance any bit-rot
will spread...
Now I'm in muti user mode .. but then if I
do a "ps -alx" I get:
TTY F S UID PID PRI ADDR SZ WCHAN COMMAND
?: 3 S 0 0-100 1227 2 5676 ????
?: 1 W 0 1 40 1324 6 5740 -
The ps command doesn't show the /etc/init
process explicitly, although
I'm pretty sure it is running.
No, it's there: the second line (PID 1). For some reason, the code for
/etc/init (in V6 at least, I don't know anything about V5) bashes the command
line so it just has '-' in it, so it looks just like a shell.
I fixed my copy so it says "/etc/init", or something like that. The machine
my source is on is powered down at the moment; if you want, I can upload the
'fixed' code tomorrow.
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, but I don't recall the
details (too lazy to look for the note I made about the bug; I can look it up
if you really want to know).
Would it be safer to just go to single user and
then shut it down?
I don't usually bother; I just log out all the shells except the one on the
console, so the machine is basically idle; then do a 'sync', and shortly
after than completes, I just halt the machine.
Noel
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2:36 p.m.
New subject: single user mode in v5 & v6
On Fri, Jan 9, 2015 at 9:23 AM, Ronald Natalie <ron(a)ronnatalie.com> wrote:
If I recall, our V6 system would go from singe user to
multiuser when you
logged out of the single user shell (our init checked the switch register
to determine whether to bring up single or multiuser).
That is the behavior I remember, also.
2:36 p.m.
New subject: single user mode in v5 & v6
On Fri, Jan 9, 2015 at 1:18 AM, Noel Chiappa <jnc(a)mercury.lcs.mit.edu>
wrote:
Just out of curiousity, why don't you set the SR
before you boot the
machine?
That way it'll come up single user, and you can icheck/dcheck before you go
to multi-user mode. I prefer doing it that way, there's as little as
possible
going on, in case the disk is slightly 'confused', so less chance any
bit-rot
will spread...
Right and it's probably worth digging up the v6 version of fsck. I had it
on tape but I worry that it might be 800 bpi which I have lost the ability
to read. I need to find a working TS08.
Also remember for early UNIX, ps "knew" about some kernel data structures
and had to compiled with the same sources that your kernel used if you want
all the command field in particular to look reasonable.
I've forgotten when that got fixed, my memory is that V7 still had vestiges
of that issue i.e. it was not until post 4.1BSD that got ps got more
independant. That said, until V8 and /proc that user mode utilities like
that got really cleaned up.
Clem
2:44 p.m.
New subject: single user mode in v5 & v6
If I recall, PS read /dev/kmem to get the proc structure which was a table of all the
active processes.
The user structure of the currently running process is the only one that is guaranteed to
be in memory (the others could be paged out)
and at least on our system was always located at 0140000. Any processes that were
swapped you could read the user structure
so things that were stored there were often unavailable (particularly the command name).
Yeah, so ps had intimate knowledge of the
layout of the kernel user and proc structures.
We moved a short version of the command name into the proc structure for reason. We
added a new TTY special character ^T
(borrowed that from the KA-10 guys) to do a brief listing of the processes controlled by
the current terminal from within the kernel. (Mike Muuss did this while he was playing
with scheduler hacking).
Also remember for early UNIX, ps "knew" about some kernel data structures and
had to compiled with the same sources that your kernel used if you want all the command
field in particular to look reasonable.
4:52 p.m.
New subject: single user mode in v5 & v6
Right. We did some similar stuff at CMU. One other hack we had was science compiled ps
with the kernel IIRC we had a table of sleep addresses so that ps could print the actual
thing you were waiting for not just an address. I think that was a Dan Klein hack.
Yeah the ^T hack was implemented a number of times. Masscomp is the only product kernel
that I knew supported it. I did miss it for a long time
Clem
Sent from my iPhone
On Jan 9, 2015, at 9:44 AM, Ronald Natalie
<ron(a)ronnatalie.com> wrote:
If I recall, PS read /dev/kmem to get the proc structure which was a table of all the
active processes.
The user structure of the currently running process is the only one that is guaranteed to
be in memory (the others could be paged out)
and at least on our system was always located at 0140000. Any processes that were
swapped you could read the user structure
so things that were stored there were often unavailable (particularly the command name).
Yeah, so ps had intimate knowledge of the
layout of the kernel user and proc structures.
We moved a short version of the command name into the proc structure for reason. We
added a new TTY special character ^T
(borrowed that from the KA-10 guys) to do a brief listing of the processes controlled by
the current terminal from within the kernel. (Mike Muuss did this while he was playing
with scheduler hacking).
>
>
> Also remember for early UNIX, ps "knew" about some kernel data structures
and had to compiled with the same sources that your kernel used if you want all the
command field in particular to look reasonable.
>
>
3393
days inactive
3393
days old
5 comments
4 participants
participants (4)
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Clem Cole -
Clem cole
-
jnc＠mercury.lcs.mit.edu -
Ronald Natalie