Section I. INTRODUCTION TO UNIX Advanced Unix Concepts On Unix systems there is a special user called root (also known as the super user or privileged user) who has complete control over all processes and files/directories, regardless of permissions or ownership. Only root may use many system commands, especially those that change the configuration of the system. Environmental Variables You may easily customize your environment by setting variables to specific values to suit your needs; most are pre-defined for you by the system administrator but can be changed. Depending on which command interpreter (shell) has been defined for you, variables are set in configuration files that reside in your home directory. The Bourne shell executes commands and sets variables defined in the .profile file, while the C-shell first executes the .login file, then the .cshrc file. The .cshrc file is also executed every time the csh command is executed on the command line. When you log off using the C-shell, the commands found in the .logout file are executed. *** Note *** Be extremely cautious modifying configuration files; it is advisable to first copy the file to a backup copy. Some useful commands which can be included in your .configuration file(s) are: alias - if you put a line in your .cshrc file like: alias lo logout you can then enter lo which the shell will expand to logout. This is particularly useful for long, complicated commands. history - a line containing: set history=100 will cause the shell to store up to the last 100 commands. To display the history list, enter: % history at the command prompt and the history list will be displayed. To re-execute the 13th command, enter: % !13 To save the history list as a log of your activities, add the line: history >>~/history.log to your .logout file. prompt - setting this variable, your prompt can look like whatever you choose. stty - stty commands can be used to change the value of terminal configuration variables (see man pages). There are many commands which display information, or do specific tasks to help you manage your environment. Some useful commands are: passwd - changes your password ps - displays processes and status kill - used to terminate a locked process quota - reports current disk usage and limits find - searches the filesystems for files/directories df - reports filesystems currently mounted and disk usage statistics w - reports who is logged on the system *** Note *** 1) see the on-line man pages for syntax of specific commands 2) see Unix Command Summary for other useful commands One of the great advantages of Unix is the ability to run commands detached from the terminal you are using. To run a process in the background, simply append an & (ampersand) to the end of the line. Example: % ls -lR / >~/all.files & causes a long, recursive listing of the entire filesystem, putting the output into a file called all.files in your home directory, running detached from your terminal. To display the status of any such jobs, enter the command: % jobs With three processes running in the background, to bring job 2 to the foreground, enter: % fg %2 To move a command running in the foreground to the background, enter: % ^Z to stop the job, then % bg Note: Not all shells support job control.
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