Xpra - X Persistent Remote Applications

	Xpra (X Persistent Remote Applications) ... is a remote display solution for forwarding applications and desktop screens. Applications forwarded by Xpra appear on the local desktop as normal windows (seamless mode), rather than being all "trapped in a box together" (full desktop mode) like with VNC. Xpra uses a custom protocol that is self-tuning and relatively latency-insensitive, and thus is usable also over worse links. Xpra allows disconnection and reconnection without disrupting the forwarded application. Xpra is an open-source software for multiple platforms (Linux, Windows, MaxOS, etc.). Homepage: ​http://www.xpra.org Wiki: ​https://www.xpra.org/trac/

Preparation

Download & Installation Xpra-client (>= 0.14.x, we recomment >=1.0.1)

• ​Linux (various distributions)
  • ​RPM install instructions
  • ​DEB install instructions
• ​MacOSX (>=10.5)
  • ​PKG format (best choice)
  • ​DMG format
  • On MacOSX >= 10.12.2 Xpra currently must be installed on the system and cannot be started directly!
• ​Windows (>=XP)
  • AntiVirus programs like 'Kaspersky' slow down startup of Xpra a lot(!) the first few times you call it.
    It can take more than a minute until the GUI appears, when the Antivirus checks the application in detail.
    Please be patient and blame your AntiVirus application (you could also add an exception for Xpra in the AntiVirus app).

Authentication

Xpra must communicate with JURECA via Secure Shell (SSH) and JURECA requires authentication to be password-less using SSH key-pair.
Please test your system before you proceed.

Execute the command with your JURECA-userid on your local workstation.
It must return the word 'success' for a successful SSH connection to JURECAVIS.

Linux/MacOSX:
ssh <YOUR-USERID>@jurecavis.fz-juelich.de echo "success"

Windows/Putty:
"C:\Program Files (x86)\PuTTY\plink.exe" -ssh <YOUR-USERID>@jurecavis.fz-juelich.de echo "success"
Ensure you have loaded your key in PuTTY´s SSH key agent called Pagent before!

Quick Howto (Linux/MacOSX only)

Start JURECA application directly from your workstation:

client> xpra start ssh:<USERID>@<LOGINNODE> --start-child=<JURECA_APP> --min-quality=90

• password-less authentication using SSH must be ensured
• set minimum quality to level 90 (unset:0, lowest:1, highest:100)

General approach using Xpra requires three steps.

1. Start application in Xpra-server on a JURECA login node.
2. Connect with Xpra-client from workstation to Xpra-server
3. Check if Xpra-server stopped on the JURECA login node.

1. Start application in Xpra-server

Login to any JURECA login node and start application with Xpra-server

• simple X11 application

  jureca> xpra start --start-child=xterm --min-quality=90
  

• OpenGL application

  jurecavis> xpra start --start-child="glxgears" --min-quality=90
  

  • using VirtualGL for hardware accelerated server-sider rendering on the GPU if available
  • vglrun is automatically put in front of the command, if vglrun exists on the node
  • currently only on JURECAVIS login nodes (jurecavis01.fz-juelich.de or jurecavis02.fz-juelich.de)

Take a note of the <DISPLAYID> and the <LOGFILE> Xpra returns:

> Actual display used: :<DISPLAYID>
> Actual log file name is now: <LOGFILE>

2. Connect with Xpra-client from workstation to Xpra-server

Start the Xpra-client on the workstation to connect to the Xpra-server on JURECA.

• Connect using Xpra command line (primarily with Linux or MacOSX)

  client> xpra attach ssh:<USERID>@<LOGINNODE>:<DISPLAYID>
  

• Connect using Xpra GUI (primarily with Windows)

  client> xpra_launcher
  

  

Mode = SSH
<USERID>@jurecavis01.fz-juelich.de:22:<DISPLAYID>

3. Check if Xpra-server stopped

The Xpra-server shuts down automatically, when the application is closed.
Check if that is the case and stop it manually if required.

jureca> xpra list
jureca> xpra stop :<DISPLAYID>

Attention:
If you stop the Xpra-client without closing your application, your application keeps on running!
This can use cpu and memory resources others might need.

Real-case scenarios with Xpra

ParaView with full serverside rendering support using VirtualGL

client> xpra start ssh:<USERID>@jurecavis01.fz-juelich.de --start-child=xterm --min-quality=90

xterm> module --force purge
xterm> module load Stages/Devel
xterm> module load GCC/5.4.0
xterm> module load ParaStationMPI
xterm> module load ParaView
xterm> paraview

More on Xpra

Full documentation of Xpra command: ​http://xpra.org/manual.html
Configuration Options: ​https://xpra.org/trac/wiki/Configuration

Usefull examples:

• List all running Xpra-server:

  xpra list
  

• Get all infos of a running Xpra-server:

  xpra info :<DISPLAYID>
  

• Start Xpra-server with larger/smaller fonts

  xpra start --start-child="xterm" --dpi=96 --min-quality=90
  

• HTML5: You want Xpra in a web-browser? Check this:
  ​http://hackaday.com/2017/03/31/linux-fu-applications-on-the-web/

Background Information

Authentication:

Xpra must communicate with JURECA via Secure Shell (SSH).
It is mandatory that JURECA trusts Xpra and is 100% sure
that the incoming connection is by a certain user and no none else.

Hence, each new SSH connections starts with an authentification procedure.
SSH supports different authentification methods, but not all are available on any site.
Xpra must be used with the most secure Public-Key Authentification (PKA) to connect to JURECA.

PKA is based on a SSH key-pair with a private key and a public key.
The private key never leaves the local machine and the public key must be installed on the remote machine.
Anyone who knows the private key can now connect to the remote machine.

Xpra Wrapper

On JURECA Xpra is started through a wrapper script, which loads the Xpra module before calling Xpra:

module use /usr/local/software/jureca/OtherStages
module load Stages/Devel
module load GCCcore/.5.4.0
module load Xpra

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any feedback welcomed - h.zilken@…, j.goebbert@…