Re: [TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation
3 Dec
2015
3 Dec
'15
3:21 p.m.
From: Will Senn <will.senn(a)gmail.com>
I am studying Unix v6 using SimH and I am documenting
the process
I did a very similar exercise using the Ersatz11 simulator; I have a lot
of stuff about the process here:
http://www.chiappa.net/~jnc/tech/V6Unix.html
It contains a number of items that you might find useful, e.g.: "V6 as
distributed is strictly a 20th Century operating system. Literally. You can't
set the date to anytime in the 21st century, for two reasons. First, the
'date' command only take a 2-digit year number. Second, even if you fix that,
the ctime() library routine has a bug in it that makes it stop working in the
closing months of 1999."
the PDP architecture
Technically, a PDP-11 - there were a number of different PDP architectures:
https://en.wikipedia.org/wiki/Programmed_Data_Processor
is a decent listing of them; several (PDP-8, PDP-10, etc) were very popular
and successful.
A few things I noted in your first post:
I am using the Ken Wellsch tape because it boots and
is stated to be
identical to Dennis Ritchie's tape other than being bootable and having
a different timestamp on root.
The only differences I could discover between the two are that in the Wellsch
versions i) a Western Electric rights notice (which prints on booting) has
been added to ken/main.c, and the Unix bootable images; and ii) the RK pack
images do have, as you noted, the bootstrap in block 0.
Note: sh is critically important, don't muck it
up :). The issue is
that if you do, there really isn't an easy way to recover.
One should _never_ install a new shell version as '/bin/sh' until it has been
run and tested for a while (for the exact reason you mention). Happily, in
Unix, as far as the OS is concerned, the command interpreter is just another
program, so it's trivial to name a new binary of the shell 'nsh' or
something, and run that for a while to make sure it's working OK, before
installing it as '/bin/sh'.
a special file (whatever that is)
Special files are UNIXisms for 'devices'. _All_ devices in Unix appear as
'special files' in the file system, usually (but not necessarily) in /dev -
that location is a convention, not a requirment of the OS.
Noel
3 Dec
3 Dec
5:27 p.m.
New subject: Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation
On 2015-12-03, Noel Chiappa wrote:
I did a very similar exercise using the Ersatz11
simulator; I have a lot
of stuff about the process here:
http://www.chiappa.net/~jnc/tech/V6Unix.html
It contains a number of items that you might find useful, e.g.: "V6 as
distributed is strictly a 20th Century operating system. Literally. You can't
set the date to anytime in the 21st century, for two reasons. First, the
'date' command only take a 2-digit year number. Second, even if you fix that,
the ctime() library routine has a bug in it that makes it stop working in the
closing months of 1999."
I don't think your fix to the date command is accurate. The description says:
The 'date' command has been extended to
support 2- and 4-digit year
numbers (to be upwardly compatible, the 2-digit ones assume 19xx).
But the code says:
if ((y < 0) || (yh < 0)) {
time(nt);
y = localtime(nt)[5];
y =+ 1900;
}
else
y = yh + y;
To match your description it should be
if ((y < 0) && (yh < 0)) {
time(nt);
y = localtime(nt)[5];
} else if(y < 0) {
/* yh = two digit year */
y = 1900 + yh;
} else
y = yh + y;
Though I'd be inclined to add "if (y < 1970) y =+ 100;" to bring it in
line
with modern systems' 1970-2069 range for two-digit years.
Of course, _any_ ancient unix system (and a fair few modern ones) can't
represent dates past 2038. We've only got 23 years left before attempts to
bring up old systems will need some trickery (maybe set the year to 28 or 56
years before the present... that trick, with increasing windows, will work
until 2100 isn't a leap year)
On the other hand, treating it as an "unsigned" value will last about as long
and is a bit less of a hack. But as you note, doing this sort of thing in V6 C
isn't trivial.
6:46 p.m.
New subject: Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation
Noel,
Thank you for writing and responding to my writeup. I have replied
inline, below:
On 12/3/15 9:21 AM, Noel Chiappa wrote:
Thanks for reminding me about your work. I had scanned it briefly when I
was first starting down this road, but wrote it off because I wasn't
using the Ersatz11 simulator. With the background I have now, it should
be translate into my current frame and be useful. I haven't tried
tackling the time problem yet, but I will keep your document in mind
along with Wolfgang's fixes for ctime:
http://www.tuhs.org/Archive/PDP-11/Bug_Fixes/V6enb/
Oops. I will be more careful in how I refer to the PDP-11
from now on.
This is a duh moment for me. I will change
the note to reflect testing
first, then copy over.
I have since learned a lot more about this and will update the note.
Regards,
Will
From: Will
Senn <will.senn(a)gmail.com>
I am studying Unix v6 using SimH and I am
documenting the process
I did a very similar exercise using the Ersatz11 simulator; I have a lot
of stuff about the process here:
http://www.chiappa.net/~jnc/tech/V6Unix.html
the PDP architecture
Technically, a PDP-11 ... The only differences I could discover between the two
are that in the Wellsch
versions i) a Western Electric rights notice (which prints on booting) has
been added to ken/main.c, and the Unix bootable images; and ii) the RK pack
images do have, as you noted, the bootstrap in block 0.
Thanks for this. I will
update my note appropriately.
Note: sh is
critically important, don't muck it up :). The issue is
that if you do, there really isn't an easy way to recover.
One should _never_ install a new shell version as '/bin/sh' until it has been
run and tested for a while (for the exact reason you mention). Happily, in
Unix, as far as the OS is concerned, the command interpreter is just another
program, so it's trivial to name a new binary of the shell 'nsh' or
something, and run that for a while to make sure it's working OK, before
installing it as '/bin/sh'. a special file (whatever that is)
Special files are UNIXisms for 'devices'. _All_ devices in Unix appear as
'special files' in the file system, usually (but not necessarily) in /dev -
that location is a convention, not a requirment of the OS.
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days old
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