How to ... Work with the OS (Operating System)

Once you're logged in to a NERSC machine, you'll be presented with a UNIX shell prompt and you'll normally be in your home ($HOME) directory. If you are new to UNIX, you'll have to learn the basics before you can do anything useful at NERSC. Some helpful web pages are listed on our UNIX training resources page.

Shells and Initialization Files

You have a choice of login shells, including csh, tcsh, bash and ksh. Please see Shells and Scripting for more information on these shells. You change shells through the NIM web interface. See Change Default Login Shell.

In your home directory, you will find default shell initialization files: .login, .cshrc, .profile, .kshenv. These are symbolic links to system defined files. You cannot modify them and you should not overwrite them. Make all customizations in auxiliary files named .login.ext, .cshrc.ext, etc.. These files are sourced from the .login, .cshrc, etc. files.

A warning: Do not copy initialization files from other machines to NERSC machines, or from one NERSC machine to another. Such copied files are unlikely to work properly.

Modules

It used to be that every time you wanted to use a new software package or library, you had to edit your shell initialization files. Those days are almost gone thanks to an extension to the UNIX system known as modules. See Modules Approach to Environment Management.