A Luser's Guide to ITS
Disclaimer: I write this as friendly advice to new users of ITS,
and the term "[1]luser" is not meant degeneratively. I'm still
discovering ITS myself, and while I know PDP-10 assembly language,
[2]TECO and DDT from my TOPS-20 days, I'm probably still an ITS
luser myself. I'm working on it, though...
[2] http://www.hactrn.net/sra/alice/
ITS is an open system
[3]Alice's PDP-10 [with feelin']
You can hack anything you want, with TECO and DDT.
You can hack anything you want, with TECO and DDT.
$U in and begin to hack.
Twiddle bits in a core dump and write 'em back.
You can hack anything you want, with TECO and DDT.
(But be careful typing <RET>)
With TECO and DDT!
[3] http://www.hactrn.net/sra/alice/alices.pdp10
It is important to understand right away that ITS is a very open
system. While you may not be able to log in without an account, you
can still read people's mail after just connecting to the system,
and once you are logged in "you can hack anything you want with TECO
and DDT", or indeed shoot yourself in the foot rather severely.
There is no file protection.
If you write/delete files in some of the system directories,
this is logged, but this is about it. Luckily files can exist
in more than one generation/version, so if you overwrite a
file the old one (may) still be around.
There is little process protection.
Although processes can't poke eachother by mistake, users
can, e.g., take over other users' processes, debug them, etc.
This is good, since it lets hackers help others.
There is little system protection.
For example, anyone (logged in) can take the system down by
using the [4]LOCK program. The minimum warning time is five
minutes, allowing others to undo the shutdown if necessary,
but since all programs can be patched at runtime, the limit
can also be circumvented (if you know how).
So some "[5]ethics" are necessary. Try not to break things, but do
explore and experiment! And don't forget to have fun!
[5] http://hacks.mit.edu/Hacks/misc/ethics.html
What not to do
* Don't overwrite files in other directories than your own. If you
do it anyway, please let someone know so they can perhaps do
something about it. ([6]Here is a piece of TECO for your EMACS
init file to help against involuntary disasters.)
* Please try to shut the system down nicely if you have to,
instead of crashing it (or its host system). This minimizes the
risk of filesystem breakage.
[6] http://victor.se/bjorn/its/emacs.php
What to do
1. Connect using Telnet, or preferrably [7]Supdup. [8]Supdup (the
Super-Duper Image Telnet protocol) allows ITS programs (such as
EMACS and PEEK) to display faster and better on your terminal
(window) than using Telnet.
2. If you don't get a * prompt, press 〈CTRL〉-Z (henceforth ^Z) to
get attention from the ITS system.
3. You are now talking to PWORD, a replacement for HACTRN which
allows only a small number of commands. Try pressing ?. If you
want to log in, use the :LOGIN command. Once you have
successfully logged in, you're talking to the real HACTRN.
4. You will notice that what we these days mean by "commands" start
with : (colon). Once you have logged in, you can also use DDT
commands such as ^A, $L (where $ means 〈ESCAPE〉), etc. Please
study the [9]DDT Primer and Reference Manual (see below), and
for the gory details, the file [10].INFO.;DDTORD > - here are
some quick basics:
+ ^Z stops the program which is running. To let it continue,
use :PROCEED or $P (that's 〈ESCAPE〉 P).
+ ^D forgets what you typed so far on the input line.
Something like ^U in bash, but doesn't erase the line, just
prints XXX?. (And ^U does something entirely different in
HACTRN.)
+ ^^ ([11]〈CTRL〉-^) is the escape character for Supdup (at
least the C version).
+ ^_ is (probably) the Help character in EMACS, but also a
special [12]escape character in ITS, so you have to type it
twice!
+ The key marked 〈BACKSPACE〉 or 〈RUBOUT〉 or 〈DELETE〉 is
different from ^H (〈CTRL〉-H). The first typically removes
the previous character. The latter (^H) typically moves
backwards through a file, or in DDT, resumes the current
program (but for full details, try :DDTDOC ^H).
5. Some useful commands (not case sensitive, but traditionally in
upper case):
[7] http://victor.se/bjorn/its/supdup.tar.gz
[8] http://victor.se/bjorn/its/supdup.php
[9] http://victor.se/bjorn/its/ddt.html
[10] http://victor.se/bjorn/its/ddtord.html
[11] http://victor.se/bjorn/its/telnet.sng
[12] http://victor.se/bjorn/its/itstty_a5.text
:DDTDOC
Shows documentation for DDT commands (i.e. not for
programs). Try :DDTDOC ^F to get documentation for the
^F command, or just :DDTDOC for interactive mode.
:WHAT
Answers questions, both silly and useful. Try :WHAT is
this or :WHAT source for NAME, or :WHAT bus (for MIT
buses in '87 or so).
:LUSER
This command calls for help from more knowledgable
hackers, if any are logged in.
:SEND
:SEND user message^C
sends a message to user. If the user is logged in, the
message is displayed on his/her terminal. If you get a
message and don't see it or want to re-read it, press
^A in HACTRN. (:SEND is similar to write in u*ix, but
better.)
:KILL
kills the current "job" (subprocess). To see which jobs
you have, use :JOBS (or $$V); to switch between them,
use :JOB (or $J) (or :JOB jobname or jobname$J).
:EMACS
This is the original EMACS! Not really as powerful as
the follow-ups (FSF Emacs, XEmacs), but leaner and
meaner. Written in the "write-only" language TECO. Try
M-x Teach Emacs to learn.
:PEEK
Similar to top in u*ix, but show more kinds of
information. Try pressing ?. Pressing Q quits.
:FINGER, :F, :NAME, :N, :WHEN, :WHOIS
These commands show information about who is logged in,
and take an optional user name as argument, showing
info also about non-logged-in users.
:PRINT
:PRINT file
prints file on your terminal, similar to more in u*ix.
Try :PRINT HACK;MD NEWS!
:LISTF
lists the files in the default directory. Also try :LF,
which is different.
+ For a fun introduction to more commands, read [13]The
HACTRN by Guy L. Steele.
+ For a gentle introduction to more commands, read
[14]Getting Started Computing at the AI Lab (PDF new
101222] ) especially chapter 6.
+ For a serious introduction to DDT/HACTRN, read the [15]DDT
Primer and Reference Manual, e.g. by using the command
:INFO DDT.
+ For historical information, read the [16]Wikipedia article.
6. Directories are flat (i.e., no subdirectories). Initially you'll
share home directory with other users. Do M-x List Directories
in EMACS to list them.
7. File names have four components. Each can be up to six
characters.
1. Device, ended by : (colon), e.g. DSK: or MD: (ITS host
name)
2. Directory, ended by ; (semicolon), e.g. USERS1;, .TEMP.;,
or HACK;.
3. "FN1" (File Name 1), the "main file name".
4. "FN2" (File Name 2), separated from FN1 by a space. FN2 is
used for file type (e.g. BIN) or more often for file
version/generation.
Example: "MD:.INFO.;DDTORD >".
Sometimes filenames are shown in another order, as DIR; DEV: FN1
FN2.
8. About file versions:
+ If you write a file FOO >, you create the next version of
FOO. If FOO 41 exists, you create FOO 42.
+ If you read a file FOO >, you read the latest version (or
largest version number).
+ The FN2 "<" represents the oldest (lowest) version.
+ So you may need to clean up once in a while, e.g. by using
the H command in DIRED (in EMACS).
9. If your connection is lost and you connect again, your old job
(set of processes) is probably still around.
+ Sometimes ITS detects your disconnection, "detaches" your
old job from its "terminal", and offers you to attach it
when you log in the next time. If you get prompted --Attach
Your Detached Tree-- when you log in, just press 〈SPACE〉 to
say "yes" (or 〈RUBOUT〉 for "no").
+ Sometimes ITS doesn't detect your disconnection. When you
log in again, your visible username will have a "0" (or
"1", "2" etc) at the end, and if you try :FINGER you see
your old job without the "0". You can then "reattach" the
old job (replace your new job with the old one) by using
the command :REATTACH uname/K where uname is your username
(without the "0" etc).
[13] http://victor.se/bjorn/its/hactrn.php
[14] http://victor.se/bjorn/its/AI_WP_235.pdf
[15] http://victor.se/bjorn/its/ddt.html
[16] http://en.wikipedia.org/wiki/Incompatible_Timesharing_System
Quick Ref for various commands
LOCK
The program used for (among other things) shutting down the
system cleanly.
1. Type :LOCK to start it, and it prompts you with _
(underscore).
2. To schedule a shutdown, give the command nDOWN, where n is
the number of minutes to wait (minimum 5).
3. You are now asked if you really want the system to go down.
Answer y if you really do.
4. You are then asked to enter a brief message to users, ended
by ^C. Please do.
The system will start shutting down when either the n minutes
have passed, or all users have logged out. (Please do not
quit KLH10 or shut down the host system until ITS has shut
down completely, which is visible on its console or by
observing the CPU usage of kn10-ks going up towards 100%.)
To cancel a shutdown, use the REVIVE command of LOCK.
_________________________________________________________
From HUMOR;JARGON 68 [August 1983]:
LUSER
See USER.
USER n.
A programmer who will believe anything you tell him. One who
asks questions. Identified at MIT with "loser" by the
spelling "luser". See REAL USER.
[Note by GLS: I don't agree with RF's definition at all.
Basically, there are two classes of people who work with a
program: there are implementors (hackers) and users (losers).
The users are looked down on by hackers to a mild degree
because they don't understand the full ramifications of the
system in all its glory. (A few users who do are known as
real winners.) It is true that users ask questions (of
necessity). Very often they are annoying or downright
stupid.]
_________________________________________________________
© [17]Björn Victor [18]<Bjorn@Victor.se>
[17] http://victor.se/bjorn/
[18] mailto:Bjorn@Victor.se
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