Basic Unix Use
By Lord Lawless
Board of Directors
March 8, 1987
This file is basically a brief introduction and overview for the beginning
hacker to the Unix operating system. All information contained herein is
accurate to the extent of my knowledge. This file is intended for inform-
ational purposes only and the author (Lord Lawless) is in NO way responsible
for the use of this file for purposes other than the aforementioned.
Part I: What is Unix?
Unix is an operating system, so designated because it allows a user to
interface with a computer in a way that is (hopefully) easy for the user to
learn and use. Unix can be known by other forms, PC-Unix, Xenix, etc., but
they all basically are the same (with slight differences this file won't go
into) and use the same commands. Unix is a wonderfully simple to use OS once
you begin, and while this file will help you I recommend that you find a Unix
system somewhere and wander around on it to help yourself to learn. To put
this more formally:
The UNIX system is a set of programs that include a time-sharing
operating system and a set of utility programs. The operating
system has two basic parts:
1) The kernel is the program in the UNIX operating system
that is responsible for most operating system functions. It
schedules and manages all the work done by the computer and
maintains the file system. It is always running, and is
invisible to users.
2) The shell is the UNIX operating system program responsible
for handling all interaction between users and the computer.
It includes a powerful command language called "shell language"*.
The utility programs (usually called UNIX commands) are executed
through the shell, and allow users to communicate with each other,
to edit and manipulate files, to write and execute programs in
several programming languages, and many other things.
Part II: Recognizing a Unix system
When you connect to a Unix system you will see a message usually like
"AT&T Unix: Unauthorized use will be Prosecuted!" or just "Unix System V" or
the like. At the least you will see a prompt saying "login:". At this point,
if possible, make sure that you are in lowercase, because if the computer det-
ects that you are typing in uppercase everything you read after will be in
uppercase with lowercase denoted by a \ in front of the word. This is because
Unix is case sensitive, so be careful, reading lowercase is much easier than
reading all uppercase and slashes. Ok, so here you are at the Unix "login:"
Part III: Logging on
At this point you must enter your login, and then, if the account (
never more than 14 characters) has one, the password. Now, all Unix systems
have default accounts, and unless set by the Root System Operator no passwords.
This has been the means of infiltration by many the Unix hacker. There are two
types of accounts in a Unix, the "super user" and the "user". The super user
has access to almost everything (or everything depending on the system) and the
user basically has access to the files he owns and what he can sometimes read.
The default super user accounts on a unix are:
For passwords to these try things like SYSTEM, SYSMAN, SYSADMIN, ADMINISTRATOR,
OPERATOR, SYSOP, etc.
The default user-level accounts are:
(Note: These accounts should be entered in lower case , I merely wrote them
in upper case for easier reference.)
After being on Unix's, I have also seen the following common accounts:
STUDENT -on school run Unix's.
The maximum length of a password is 11 characters.
After doing all this you should, with luck, be in!
If you couldn't hack anything out, try typing "WHO" at the login: prompt, it
may list all the user accounts and you can try them until you find one without
Part IV: You're in!!!
Congratulate yourself, the hardest part of Unix "hacking" is over. Ok,
now that you're in you'll see a prompt which will probably look like "$" for a
user account or "#" if you got lucky and got a super user account.
(Quick note, to stop a unix process in action try typing ctrl-d or control
backspace, these are the end of file/Stop process keys.)
Ok, so you are now in. Let me give a quick lesson on Unix directories. In
Unix, the root is the main directory, and it contains subdirectories which may
contain subdirectories etc. In order to change to the root directory, one
would type "cd /". This is because "cd" is the command "change directory" and
"/" is the root directory. To change to subdirectory "Bill" contained in the
root directory, you would type "cd /Bill" or, if you were in the root dir, just
"cd Bill". If you wanted to access Bill's files, you'd enter "cd /Bill/files"
assuming Bill had a subdir called files where he kept his files. This is how
a person would move around in a Unix sys. Graphically, it looks like this:
Part V: Basic Commands
Ok, these commands are the most useful ones that I've found and can are
entered from the prompt.
Command:What it does
ls gives a listing of all files in a directory
cat gives a dump to screen of what is contained in a file. For instance
"cat phones" would show me what is in file "phones".
cd change directory
pwd shows what directory path you are in now
ps shows system processes
rm remove a file, for instance "rm phones".
rmdir removes a directory, for instance "rm Bill".
grep print ascii strings in a file, ie "grep phones"
who shows who's on the system
mail sends mail to a user, syntax mail <username>
su change from 1 account to another. For instance, if you are account
Bill and wish to change to account Jake (which is unpassworded) just
type "su Jake" and you will change to him. If Jake has a password you
will be prompted to enter it. This is useful for loggin in under a
user account and switching later to a super user account.
passwd allows a user to change his password. If you are a superuser you can
change someone elses password by typing "passwd <account>".
mkuser make a user (providing you are a super user)
mkdir create a directory
More Information about Commands
The following are more of the most basic Unix commands.
cat cd chmod cp cut date
echo egrep fgrep file find glossary
grep help ln locate ls mail
mesg mkdir mv news pr ps
pwd rm sleep sort starter stty
tabs tail tee time touch tty
uname usage wall wc who write
Using the Command: mkdir
Syntax Summary: mkdir dir_name1 [ dir_name2 ...]
dir_names are simple subdirectory names,
relative pathnames, or full pathnames
mkdir creates one or more new directories.
If mkdir is given a simple name as an argument, the new
directory will be a subdirectory of the current directory.
You can make new directories anywhere in the file system
by giving mkdir a complete or relative pathname for the new
directories, if you have permission to write in the directory
where the new directory is to be created.
Ok, those are the basic commands you will need to go around in the system.
Part VI: Useful Information
A great place to go to get information on who is on the system and
what accounts you can use to get on again is contained in the file "passwd"
in the "etc" directory. To look at it, cd etc, and then cat passwd. The
first entry should say something like this:
what this means is that the root account has an encrypted password, has super-
user capabilities (any user with a 0 in that slot is a super user) is in group
1 (relatively unimportant for this file), has a comment of Operator (this may
be blank), has a home directory of / (the root) and uses the Bourne Shell, kept
in the /bin directory.
You will then see all the other users listed out in the same format. If you
see an account followed by two colons, that means that it has no password. You
want these accounts so that you can log in under them another time. If you get
real lucky you may see something like this:
meaning that you have found a super user account with no password, a very
useful item indeed.
Another good place to look is the /usr/spool dir and the
/usr/spool/cron/crontabs dir because if you are a super user that dir contains
much that will be useful to you.
In order to move up to a directory one level higher than you are presently in,
type "cd ..". So to move from /Bill/files to /Bill I would just type cd ..
and, assuming I started in /Bill/files I would now be in /Bill.
Ok, now you can wander the system "cat"'ing around and whatnot. If a file
doesn't "cat", try just typing it's name, that will execute it if you have the
privileges. Try typing "admin" or "ua" if you are a superuser nad maybe you'll
be able to create users or other interesting things. You may not be able to
cat a file or run it because you lack access permissions. What are they? Read
access permissions: permissions: mode: owner:
As the user of a UNIX system, you can decide who can read, write,
and execute the files and directories that you own. You are
usually the owner of files and directories that you have created in
your login directory and in the "subdirectories"* in your login
directory. You may also own files in other peoples' directories.
You control the use of your files and directories by specifying the
access permissions, also called the mode, for each. You can specify
different access permissions for yourself, your "group"*, and the
other users of the system. Permission to read allows the user to
read the contents of the file. Write permission allows the user to
change the file and execute permission enables the user to execute
the program within the file.
prints the access permissions for each file and directory in the
current directory. The sample listing below shows the mode of the
file (preceded by a -), the number of "links"*, the owner, the
"group ID"*, the size in characters, the date and time the file
was last modified, and the "filename"*.
-rwxr-x--x 1 sandy 12345 128 Oct 9 9:32 lock
If this were a listing for a directory, the hyphen (-) would be
replaced by the letter d. The owner of the file "lock" can read,
write and execute the file, the group can read and execute it, and
the others can only execute it. You can change the mode of your
files and directories by using the change mode command, chmod.
Other interesting places to look are in the directories assigned to the users
on the Unix system, often their files will contain some useful information.
Also try going into the /uucp directory or looking for any uucp dir anywhere as
it may contain phone numbers to other Unix systems or other "goodies".
The *: asterisk
In the shell, an asterisk matches any "string"* of characters in
a "filename"* on a command line. The command
removes all files from the current working directory that begin with
the string "temp". Files like "temp", "temp1", "temp.1", and
"temp.save" would all be deleted. An asterisk alone matches any
filename in the current working directory except those beginning
with "dot (.)"*. For example,
removes all the files in your directory except for the dot (.)files.
Finally, typing help at the unix prompt may bring up a help manual that is
usually quite well done and will help you if you are stuck or wish to explore
in more depth the commands I didn't go into.
Hmm, what else? I can't think of much more right now that would help you much
more, in this file I think I've covered everything that should get you well on
your way towards becoming a unix hacker. Once you've got this, start reading
files on "Unix Shells", "Scripts", and ask around A LOT. Ah, I just remembered
something. To get help on a command, type "man <command>" or "whatis <command>
" and you may find out. Also, a lot of Unix's have a built in Help feature
somewhere, try to get to it.
Part VII: A Few Final Words
If you manage to get onto a Unix system, don't screw it up. Unix is a
great operating system, and fun to learn on and have other people learn on.
Don't become a superuser and delete everything or other things, it's just not
worth it. Also, don't make a use called "Hacker" or "Shadow 1" or something,
that's a blatant giveaway. Put an account a little out of the way directory,
and create user level accounts if you must, and perhaps just 1 super user
level. I can't think of much more to say on the basics, though I probably left
some important things out....nobody's perfect. I hope you enjoyed the file and
I can be found on the following boards:
The Private Connection
The Undergraduates Lounge
Phreak Klass 2600
Slaughterhouse 5, Holovision Network Node 1
Special Thanks to: The Prophet, for his excellent file: Unix Use and Security
From the Ground Up.
The End, good luck, enjoy yourself, and don't get caught!
--This has been a Lord Lawless Presentation, (C) 1987.--