====== Access to the Laboratory Computer ======

{{section>deng:praktikum:a12:status#Laboratory computer&noheader}}

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.


===== External Login =====

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.


==== Requirements ====

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.

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To access the analysis computer from outside the university network, you must first connect to the university network via VPN. Instructions can be found on the [[https://www.uni-potsdam.de/de/zim/angebote-loesungen/vpn | ZIM website]].
</WRAP>


==== Linux / Unix ====

Since all astrophysics computers run Linux, logging in from another Linux/Unix system is straightforward. In most cases, a simple [[https://en.wikipedia.org/wiki/Secure_Shell | 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.


=== Xpra ===

Alternatively, you can use [[https://www.xpra.org/|Xpra]], which also uses //SSH// but allows more stable work with graphical applications, especially on slower connections.

After installation, a connection can be established with:

   xpra seamless ssh:alpha@columba.astro.physik.uni-potsdam.de --start=konsole

The command is similar to the SSH login above. Replace **alpha** with the appropriate group name.

After a successful connection, an //Xpra// icon or menu usually appears on the desktop (under Ubuntu in the upper-right corner near network/volume/battery indicators). From this menu, programs can be started directly on the remote system. The application windows integrate seamlessly into the local desktop.

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


==== Windows ====

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 ===

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

  * [[http://mobaxterm.mobatek.net/|MobaXterm]]

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


=== PuTTY and Xming ===

**Required software**

  * [[http://www.chiark.greenend.org.uk/~sgtatham/putty/|PuTTY]] (SSH client)
  * [[http://www.straightrunning.com/XmingNotes/|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


==== Operating System Independent ====

=== X2Go ===

An //X2Go// server is installed on the laboratory computer **columba**, allowing efficient remote work with graphical applications. The X2Go client is available for all major operating systems, including Windows, Linux and macOS.

{{ :ost:software:x2go_main_window.png?direct&400 |}}

After installing the client, create a new session via //Session → New session ...//.

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{{ :ost:software:x2go_main_settings.png |}}
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{{ :ost:software:x2go_input-output_settings.png |}}
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Configure the following parameters:

  * **Session name**: arbitrary
  * **Host**: ''columba.astro.physik.uni-potsdam.de''
  * **Login**: e.g. ''alpha''

In the ''Input/Output'' tab:

  * Enable **Fullscreen**
  * Disable **Set display DPI**

After clicking ''OK'', start the session by double-clicking the entry. You will then be prompted to enter your password:

{{ :ost:software:x2go_4.png |}}

<fc #ff0000>Attention Wayland users:</fc>
If the client crashes, try starting it via:

    env QT_QPA_PLATFORM=xcb x2goclient


=== Remote Desktop Protocol ===

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This method is currently in beta.
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This method is currently not working reliably.
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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.

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** Linux **

On Linux, [[https://remmina.org/ | 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.

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<WRAP half column>.
[{{ost:software:remmina_rdp_initial.jpg|}}]
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<WRAP group>
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[{{ost:software:remmina_rdp_basic_setup.jpg| Basic setup}}]
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[{{ost:software:remmina_rdp_ssh_tunnel.jpg| SSH tunnel}}]
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<WRAP group>
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[{{ost:software:remmina_rdp_advanced_setup.jpg| Additional options}}]
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[{{ost:software:remmina_rdp_final.jpg| }}]
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<WRAP group>
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** 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. 

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[{{ost:software:windows_rdp_client_setup.jpg| RDP Windows Client}}]
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===== External Login from the Physics Computer Pool =====

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).


===== Working Directly on the Data Reduction Computer =====

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


===== File Transfer via SFTP =====

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 [[http://winscp.net/eng|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.


===== Linux Cheat Sheets =====

   * [[http://www.cheat-sheets.org/saved-copy/fwunixref.pdf|Basic commands]]


[[en:praktikum:index|Laboratory Courses – Overview]]