Access to the Laboratory Computer

There are two ways to analyse the data collected during the lab course: 1. Perform the analysis directly on the computer columba at the university (by prior arrangement). 2. Log in to this computer remotely from another system (e.g. from home) and perform the analysis there.

Data analysis can also be carried out remotely, either from the computer pool of the Physics Institute or from a private computer with an internet connection. Several access methods are available, each with its own advantages and disadvantages.

Credentials are provided by the supervisors or communicated during the introduction:

 User:      alpha
 Password:  will be provided

alpha is used here as an example and must be replaced by the corresponding group name.

Since all astrophysics computers run Linux, logging in from another Linux/Unix system is straightforward. In most cases, a simple SSH login is sufficient to perform the complete data analysis remotely.

Graphical output (e.g. FITS viewers or editors) is also supported, although performance depends on the connection speed. Within the university network this is usually not an issue, but from home the performance may be limited.

Login via terminal:

ssh -Y alpha@columba.astro.physik.uni-potsdam.de

You will be prompted for your password. The parameter -Y (capital Y) enables forwarding of graphical output. alpha is once again used here as an example and must be replaced with the relevant group name.

Once you have logged in successfully, you can navigate the computer’s directory tree via the terminal window and launch other programmes. You can also carry out data reduction and analysis in this way. Many guides covering the basic commands for navigation and working with files are available online (e.g. those from PhoenixNAP).

On a modern Linux system that runs Wayland (which replaces the old X11 server architecture), native Wayland programmes can be streamed directly from the columba data reduction computer to a local client system that also runs Wayland. This is achieved using the Waypipe programme, which must first be installed on most systems. Once installed, a Wayland programme can be launched as follows:

 waypipe ssh alpha@columba.astro.physik.uni-potsdam.de Wayland_programme 

Alternatively, you can use Xpra, which also uses SSH but allows more stable work with graphical applications, especially on slower connections.

In most cases, Xpra must first be installed via the package repositories. You then log in to columba via SSH as described above. Next, use the following command to start

 xpra start :10 --start=konsole

the desired programme. In this case, the KDE terminal programme Konsole.

In the next step, you can then connect to the programme running on columba from your local computer:

 xpra attach ssh:alpha@columba.astro.physik.uni-potsdam.de:10

In our case, the Konsole window should open. You can then use this window to launch other programmes. alpha is once again used here as an example and must be replaced with the relevant group name.

You can detach from a running session without terminating it:

 xpra detach

Reconnect with:

 xpra attach ssh:alpha@columba.astro.physik.uni-potsdam.de

Terminate the session with:

 xpra exit

macOS comes with a built-in SSH client that can be accessed via Terminal.

The Terminal can easily be opened via a Spotlight search (Cmd + Space) by entering the search term “Terminal” (see also Apple documentation). An SSH connection can then be established in the same way as on Linux:

ssh alpha@columba.astro.physik.uni-potsdam.de

macOS does not natively support X11. In order to forward graphical applications via SSH (X11 forwarding), you must first install XQuartz, which is a free X11 implementation for macOS. XQuartz can be downloaded from the official website (xquartz.org). After installation and restarting the system, X11 forwarding can be used as follows:

ssh -Y alpha@columba.astro.physik.uni-potsdam.de

Since Windows does not use the X-Window system, graphical output from Linux systems cannot be displayed directly. Therefore, an additional X server (X11 server) must be installed.

Recommended tools are:

MobaXterm is an SSH client that includes a built-in X11 server.

• MobaXterm

To improve connection stability, it is recommended to enable the SSH keepalive option and restart the program.

Required software

• PuTTY (SSH client)
• Xming (X server)

Xming should be installed and ideally started automatically with the system. PuTTY requires only minimal configuration:

• Enter columba.astro.physik.uni-potsdam.de as hostname in the Session menu
• Enable X11 forwarding under Connection → SSH → X11
• In case of problems with the graphical output, set localhost:0 as the display location

In addition to the above methods, you can log in to columba using the Remote Desktop Protocol (RDP). This protocol, developed by Microsoft, is highly efficient and enables the entire desktop to be displayed without any significant loss of speed. There is a free Linux implementation, so we can use this with columba too. However, as RDP is not considered the most secure method, you must first establish an SSH tunnel to Columba before connecting to the RDP server.

Linux

On Linux, Remmina is the recommended option:

• Start the program and create a new connection
• Enter a name for the configuration
• Server: 127.0.0.1:3389
• Enter username and password
• Enable Use client resolution

Under SSH Tunnel:

• Enable SSH tunnel
• Server: columba.astro.physik.uni-potsdam.de
• Enter username and password

Start the connection via Save and Connect.

If you are satisfied with the connection speed, the Advanced tab allows you to improve the quality of your connection.

.

Basic setup

SSH tunnel

Additional options

Windows 11

Firstly, an SSH tunnel must be created using PowerShell, as the Windows RDP client does not support this:

 ssh -L 3399:127.0.0.1:3389 alpha@columba.astro.physik.uni-potsdam.de

You can then connect using an RDP client. The following settings must be configured:

• Computer: localhost:3399
• User name: e.g. alpha
• Allow me to save credentials (optional, it may be necessary to click on Show Options first)

Click Connect to establish the connection. You will then be prompted to enter your password.

RDP Windows Client

After logging in

After logging in, a window appears requesting further authentication for network services (see below). You can safely ignore this and close it.

Authentication window that appears after logging in

Methods that are currently not supported

  env QT_QPA_PLATFORM=xcb x2goclient

Termius Terminus is a modern SSH client with a graphical user interface. A free basic version is available for many operating systems.

The computers in the Physics computer pool (room 2.28.1.101) can also be used to access the laboratory computer via SSH. Due to the high network speed, efficient work is possible without prior reservation.

Accounts can be requested from Mr H. Todt (room 2.28.2.004).

The laboratory computer (columba) is available for on-site data analysis (room 2.28.2.009) and can be booked via email.

Regardless of the operating system, it is possible to log in via SFTP (SSH File Transfer Protocol) solely for the purpose of exchanging data. This requires an SFTP programme. These are available for virtually every operating system, whether console-based or with a graphical user interface. Users accustomed to a graphical user interface can use WinSCP, for example, as a free SFTP client.

The login details for the SFTP client are identical to those for SSH access:

 Server:   columba.astro.physik.uni-potsdam.de
 Protocol: SFTP
 User:     alpha
 Password: as provided

Similarly, alpha is used here merely as an example and must be replaced with the relevant group name.

Note: SFTP is intended for file transfer only. It does not allow execution of programs.

• Basic commands

Laboratory Courses – Overview