The Shell Game Part 1: What is a shell?
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The Shell Game Part 1: What is a shell?



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

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



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The Shell Game Part 1: What is a shell? The Shell Game Part 1: What is a shell? Presentation Transcript

  • The Shell Game, Part 1 Kevin O'Brien Washtenaw Linux Users Group
  • 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.” --
  • 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.
  • 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
  • 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.
  • 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
  • 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
  • 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.
  • 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
  • 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
  • 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
  • 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