To work on the devices in the ARBI rooms, you must first log in (register) with your login name and password. A login must be requested from ARBI. Proposals can be obtained directly from ARBI. You will then receive an identifier and an access password.

Each login is assigned a HOME directory in which the data is located. These can be files of various types, as well as other directories. Directories are directories, which in turn can contain files and directories. This enables a structure (file structure) to be set up that allows you to save your own data in an organised manner.

After the successful login process, a session (X-Window session) is started, which initially only consists of the window manager xfwm4 of the Xfce4 software system with its panel. The window manager displays the windows of other programmes on the screen. The window manager can also be used to start and control programmes.

In particular, the window manager can also be used to start the Xterm programme. The XTerm programme is a terminal emulator that enables you to work with the command line (TTY mode, console mode). A large number of programmes under UNIX work in TTY mode and must be started in an XTerm terminal emulator. The window of the XTerm terminal emulator is used to display the output.

Typical for working with the XTerm terminal emulator (of which there may well be several on the screen) is working with a command interpreter (shell). The shell accepts user input from the keyboard, interprets it and then executes an action. This is often the start of a programme with additional arguments and options.

Some useful UNIX commands are

ll or ls -l(long listing) Displays the files in the current directory

vi filename Calls the editor

dateDate and time

cat filename (concatenate) Show the contents of a file on the screen

more filename Browse through text file

ps aux(process status) Display process status

chown user File name (change owner) Change owner of the file

rwhoShows which users are active on the computers

kill -9 pidCancel process

pwd(print working directory) Display current directory

cd directory name (change directory) for navigating in the file structure

cp file1 file2 (copy) Copy files

mv file1 file2 (move) Move or rename files

rm filename (remove) Delete files

mkdir directory (make directory) Create directories

rmdir directory (remove directory) Deleting directories

man command name (manual page) Retrieve a manual page.

In addition, TTY-based application programmes (i.e. programmes that work in TTY mode) are started via their command name. These can be editors, compilers, email programmes, etc. In some cases, the entire window of the XTerm terminal emulator is used for the output. The prompt to enter further commands (system prompt) only appears on the screen again after the programme has ended.

Command lines can have additional effects through all kinds of special characters, each of which has a special meaning for the command interpreter used (the shell). For example, output or input redirection to or from files, linking the output of a programme with the input of another programme (pipes), starting a programme depending on the success status of the previously terminated programme, etc. The Bourne shell (sh, /bin/sh), the Korn shell (ksh, /bin/ksh), the Bourne-Again shell (bash, /usr/local/bin/bash) and the Z shell (zsh, /usr/bin/zsh) are used as command interpreters.

In addition to the programmes in TTY mode, there are a number of GUI programmes (GUI = Graphical User Interface). These programmes are displayed in their own windows on the screen. The GUI programmes can be started in an XTerm terminal emulator or from the window manager. The XTerm terminal emulator may be blocked for further use until the GUI programme is terminated. The window manager may first have to be configured to start GUI programmes.

A typical GUI programme is 'nedit', which can be started from the tool bar of the window manager. The nedit programme is an editor for editing files using graphical elements that can be controlled with the mouse and keyboard.

The structure of the X session in the default setting is only a suggestion created by the first semester tutors. All programmes started in the default settings have alternatives or can be adapted to your own needs and wishes. The details can be found in the respective documentation, mostly manual pages. Experimentation is worthwhile and is rewarded with a customised X session.

At present, a maximum of 5 GB of data can be stored in the HOME directory under FreeBSD. This limit is enforced by the operating system and cannot be exceeded (disc quota). Under Mac OS X, 1 GB is currently available. As a number of files are generally created during the logon process on the screen due to the X session being set up, exceeding the disc quota can cause the logon process to be aborted. In such a case, a telnet/login connection on the screen of a fellow student or the help of an ARBI employee must be used to delete files. If necessary, the disc quota can be increased on request.

Deleted or overwritten files that were created the day before or a long time ago can be restored from the backup copy of the file server data. An enquiry to an ARBI employee will provide clarification.