Beginning an exploration of the Linux shell by answering the question "What is a shell?"

1. The Shell Game, Part 1
Kevin O'Brien
Washtenaw Linux Users Group
http://www.lugwash.org

2. What is a Shell?
“A shell is a program that provides the traditional,
text-only user interface for Linux and other Unix-
like operating systems. Its primary function is to
read commands that are typed into a console
(i.e., an all-text display mode) or terminal window
(an all-text window) in a GUI (graphical user
interface) and then execute (i.e., run) them.”
--http://www.linfo.org/shell.html

3. Why “Shell”?
● At its most fundamental, the OS consists of a
kernel, which is the heart of the OS
● The kernel keeps track of different processes
running, gives them CPU time as needed,
handles interaction with peripheral devices,
etc.
● The Shell surrounds all of this, and creates a
way to interact with it.

4. So what is a shell?
● It is the basic way for a person to interact with
a computer
● This is done by typing in commands
● If you open a terminal window, you are using
the shell
● If you cannot boot into a GUI interface, you
can usually boot into a shell and fix things

5. Servers
● Servers commonly do not even bother to
install a GUI. Everything is done via the shell.
● This saves on resources, since you do not
have to devote RAM and CPU cycles to the
GUI, and can instead devote them to serving
files, or whatever.

6. Headless Servers
● Sometimes a server is set up without a
monitor even attached. This is called
“Headless”.
● Server administration is done via a terminal
connection of some kind, commonly via ssh

7. ssh
● Ssh stands for Secure Shell
● This is the replacement for telnet, which was
used in the old days
● Telnet is not secure, that is why it was
replaced

8. Server Administration
● Pretty much all server administration in Linux
or indeed any Unix-like operating system is
done via the shell
● This is not just because the shell saves on
resources. It is also the case that the shell is
more efficient, and more powerful, than any
GUI.

9. Tip for new users
● Buy a box of 3X5 index cards, and keep the
box by your computer
● Every time you find a useful command, write it
down. You may want to use this command
again at a later time.
● Sometimes you will want to group related
commands

10. Example Card – Fixing an Install
● Here is a set of commands I put on one card
to help me when I have a problem with an
install on my Kubuntu machine
– Sudo dpkg --configure -a
– Sudo apt-get -f install
– Sudo fuser -vik /var/lib/dpkg/lock

11. Why you need to know this
● Jaunty upgrade → No video!
● No way to launch a GUI
● But I could go into failsafe mode, and get a
shell prompt
● With the help of a command I found online, I
got my video up and running again

12. Coming attractions
● This is the first in a series of short
presentations designed for the newcomer to
Linux
● In future installments we will look at choices
among shells, techniques for the most
common shell (bash), and some tips and tricks
to help move you to being an expert