the shell game part 1: what is a shell?
DESCRIPTION
Beginning an exploration of the Linux shell by answering the question "What is a shell?"TRANSCRIPT
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The Shell Game, Part 1
Kevin O'BrienWashtenaw Linux Users Group
http://www.lugwash.org
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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
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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.
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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
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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.
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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
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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
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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.
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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
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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
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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
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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