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Margie Semilof, Editorial Director
To use the technical possibilities that GNU/Linux offers there are a range of commands that can be used. These commands need to be entered through some sort of interface. Generally the interface is text-based, and that means some mechanism has to interpret the commands. This interpreter is what we call the "shell." The difference between the shells are mainly a matter of functionality, where some are more advanced or user-friendly than others. The most popular is BASH (Bourne Again SHell) that has very nice features like a history of commands that you can access by using the up-arrow.
With "login shell," one refers to the command interpreter that is available after you log in to the system. This has little to do with the login process itself, but is more a matter of handling the entered commands. What you can do or cannot do is a matter of user rights. Generally speaking you can use any installed shell system just by entering its name as a command (in fact the shell is nothing more than a command you run on a Linux system). So if you are logging in and end up using a Bash shell you can switch, for example, to Korn, by entering "ksh." You'll notice a different behaviour. When you leave the Korn shell by entering "exit" you'll return to the Bash prompt that you used to start Korn.
Editor's note: You can learn more about the Bourne shell and the C shell in our glossary.
This was first published in October 2004