UNIX

The Unix work environment can be accessed from various machines. In this section we will look at the various ways of initiating a session on a Unix machine.

Via the X-terminals , you can initiate a graphical session on the LCFIB Unix servers.

When initiating a graphical terminal, a menu appears showing the various machines on which we can open a session. The first step is to choose the machine we want to work on from this "chooser" menu. To do this, either double-click on the name of the machine, or select it and click OK. Bear in mind that this step may not be necessary if the X-Terminal is configured to work on a single machine.

Once the desired machine is selected, a dialogue will appear, showing the name of the X-Terminal (from which we are establishing the connection) and the username and password fields.

Once the password is authenticated, a graphical session will open, with a few initial windows. From here onwards, the behaviour of the terminal depends on the window manager that is running. Usually, you can access the menus by clicking one of the mouse buttons on the desktop.

Most of the PCs in the computer rooms offer the possibility of working in Linux.

If this is the case, we can start a graphical session on a Unix system that runs on the PC itself. There is a personal area of disk space available on the PC network file server, plus the possibility of connecting to the LCFIB Unix servers that are used for teaching purposes. Connection to these servers may be established via the ssh (Secure Shell) protocol

In order to use Linux, first load the following PC initialisation instructions.

Once loaded, a dialogue will appear with the name of the PC, which asks for your username and password (as is the case with the X-Terminals). This is the same as the PC network file server password.

Once authenticated, a graphical session similar to that of an X-Terminal will load.

More information on this matter is available in the document: LCFIB Linux system description.

We can connect to all LCFIB Unix servers via the telnet protocol. It is recommended that you use this option only if there is no other, such as Secure Shell.

We would normally use the following telnet command:

        $ telnet name_of_server
      

When connected to a session, a prompt will appear to ask for our user name:

        login: 
      

We must type our user name for the machine we are connected to. All user names follow a standard format except for accounts for certain subjects (GEOC, DVLSI, GC, MGC, VRC, ASSO and DAC):

        login: d5078643
      

When we press return, the following prompt will appear:

        password: 
      

This dialogue is asking for our password, which will not be displayed on screen for security reasons. If there is an error, the system will show a message to this effect, and will ask for our user name and password again.

Once you have entered your user name and password correctly, the system will show the command line prompt, and you may begin working.

Note: Read the initial system messages and remember that UNIX is case sensitive.

Your folder will initially contain the following files:

.login

This will run once a session only when working with C-shell or tcsh. It contains, amongst other things, declarations of environment variables such as EXINIT, which is used by the vi editor; HOME, which indicates the user's working folder; PATH, which is a list of the most frequently used folders, etc.

.cshrc or .tcshrc

This is the first initialisation command file that is run when beginning a csh or tcsh session. This file runs every time a new shell is opened.

.profile

This is the Bourne shell initialisation file. It contains the commands the shell will run as it is created.

.logout

This file always runs when logging out.

. .

The folder located directly up a level from this folder is the parent directory.

.

Current folder.

Secure Shell is a remote login mechanism. It allows interactive sessions on UNIX servers to run from both UNIX and Windows machines.

Although its basic functions are the same as telnet, it holds many advantages over it:

• all communications are encrypted, so that our passwords do not travel around the network unaltered.
• it configures the X environment for the new session transparently, saving us from having to do so manually (xhost and DISPLAY),
• In addition to other functions, it allows the running of remote commands without having to open an interactive session.

The basic command syntax for ssh on Unix (and Linux) is:

         $ ssh -l user_name remote_server
      

Next, if it is the first time we are connecting to this server, it asks for confirmation, in order to accept the computer's identity. It will then ask for our password.

Once authenticated, the interactive session is started on the server, in the same way as telnet.

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