A UNIX Commands Reference
Tutorial
By ©John N. Kostaras
Introduction
This tutorial stems from and enhances a manual I once
read, “INTERACTIVE UNIX Operating System Primer – Version 3.0” [1]. It covers
both Unix and Linux releases. It is basically a quick reference of the most
common commands avoiding the bundle of information currently offered by
the man command. For a more complete reference,
however, one should either use the man command or another more complete source.
You can also download the tutorial in .pdf
format by right clicking on the Adobe icon
on the toolbar on the left and selecting
"Save Target As ..." in the pop-up
menu of IE or "Save link as ..."
in Netscape Navigator and Opera.
Getting Started
Before you can start working with UNIX, you or your system
administrator must have installed the system and set up your login account.
If your system is switched off, you must first boot the Unix operating
system. In a workstation normally, the computer where the operating system
has been installed, is on 24 hours per day, and a common user simply connects
to the main computer via a terminal. If this is the case, once you switch
on the terminal, a screen asking for a login name appears:
Login:
If however the operating system is installed in a PC (e.g. a LINUX release),
after you switch on the computer the operating system is booted. If this is
your case then you will see a number of strange messages appearing on your
screen before the aforementioned login screen appears.
Logging in
In the login prompt, type in your user identification
name (ID), or login name, assigned to you and press ENTER. After
a user ID is entered, the system may request a password:
Login: john
Password:
Type in your password (if you have been assigned one) and press ENTER. The
password is not shown on the screen so that no one watching at your display
at that time can see it.
If you have typed your login name and password correctly
the system displays the command prompt on the screen:
$
or something similar (# or %). The prompt
indicates that the system is ready to receive information. You may enter a
command or run an application when the prompt is displayed on your screen.
When you interact with the UNIX operating system (shortly OS), the commands
you type are processed by the command interpreter, which passes your
commands to the OS for processing and delivers the results to you. This interactive
command interpreter is called the shell.
Each time you log in, the OS places you in your home
directory. This is your personal working area. Like the DOS OS, the UNIX
OS consists of files and directories. A file is a collection of data
stored under an assigned name. Examples of files are a text document you type,
an executable program etc. This tutorial is also stored in a file with filename
“UNIX tutorial.doc”. A directory is a file repository. It exists only
to help you organize your files into separate thematic entities. A directory
can contain other directories (or sub-directories) and files.
Logging out
After you have finished your work with the system, you
must log out. Always logout when you are finished using the computer,
to prevent unauthorised use of your account. You can log out by one of the
following ways.
-
You can hold down the CTRL key and simultaneously press d
-
You may type the exit command at the prompt
and press ENTER
-
You may type logout at the prompt and press
ENTER.
The OS will display the login:
prompt, indicating that it is ready to accept a new login name.
Shutting down the system
If you are a system administrator you can shut down the
system. Switching off the terminal display does not shut down the system.
In a PC however, you cannot simply switch it off. You first must shut down
the OS. Because UNIX is a multi-tasking OS, the computer can be running
many different processes (programs) at the same time. For example, you may
be printing a file while at the same time you are editing another file. To
arrange for the computer to complete all the tasks that are currently running,
you should shut down first before switching off.
To shut down the computer you must first login as a system
administrator, or a user with system administrator’s privileges. If you are
then you can shutdown the system by entering the following command at the
administrator’s shell prompt (which is #):
# shutdown
and press the ENTER key. The system will ask you a number of questions
like when should the system go down etc. You should answer to these questions
with a y for yes or a n
for no. If you want however to shutdown the system immediately without being
prompted with questions you should add either now
or –g 0 or –h
0 after the shutdown command at the prompt. After a number of strange
messages on the screen, the message:
System halted
appears and the system is halted. You can then switch off the computer.
If you want to reboot the computer you should enter –r
0 after the shutdown command.
Command syntax
In a UNIX OS, the user types a command followed by the
ENTER key, the system runs the program that executes the user’s command,
and it outputs the results. The commands in UNIX are case sensitive,
which means that the system distinguishes between uppercase and lowercase
letters. Most system commands are typed in lowercase letters. A UNIX command
consists of three parts: the command name, its options, and
its arguments. Options typically begin with a dash (-). The command
name, options and arguments are separated by spaces. Thus, e.g. to shutdown
the system you should type:
# shutdown –h 0
Here is the command format I shall use in this document:
jnkostaras@mail.gr
Last modification: 19 November 2001.