About Scyld Cloud Workstation

Scyld Cloud Workstation 7.1.8, commit 9fb94c60d68a60bdb95b644ffc49b7efbc0ce5b6.


Scyld Cloud Workstation is a web server that provides secure, easy remote access to teams working on Windows and Linux workstations through standard web browsers, eliminating the need for client-side installations and changes to firewall policies.

This document describes system requirements, installation, configuration, and usage.

Release Notes


We recommend moving changes from your old config file to the latest config file.


  • Fixed native client blank connect dialogue appearing after service restarts
  • Fixed native client black screen when reconnecting after Windows 10 service restarts
  • Fixed native client scroll bars not appearing when reconnecting after Windows 10 service restarts
  • Fixed Windows 10 service becoming unavailable after signing out
  • Suppressed mouse cursors always shows in Windows 10
  • Added HiDPI support for Windows stream encoder
  • Fixed Linux log file location


  • Improved handling of scenarios where Windows has no console session
  • Improved handling of scenarios where RDP session is active
  • Documented ‘Escape’ workaround for black windows login screen issue
  • Changed default XML config file value for Server.IdleUserTimeout to 120
  • Fixed missing OpenSSL libraries in Windows
  • Fixed client EULA


  • Changed video bit-rate selection to be based on screen resolution
  • Lower latency for native client due to optimizations on color conversion and frame rendering


  • Added OpenSSL v1.0.2n libraries to Windows native-client


  • Fixed Windows password changing documentation
  • Fixed config file automatically inserting StreamVideoSource tags
  • Removed Windows wrapper batch script


  • Added 4K resolution support to native-client. Additional server-side setup is required. See the Enable 4K Support section for more information.
  • Improved frame-rate performance of native-client
  • Added MD5 hash of configuration file to start-up output
  • Upgraded QT to 5.9.2
  • Improved native-client window resize behavior
  • Improved native-client fullscreen behavior to downscale graphics when remote desktop is larger than the client screen size


  • Fixed image blurring when enabling unique frames


  • Added ability to sign in with Linux and Windows OS credentials
  • Added ability to transmit only unique video frames with Server.Video.UniqueFramesOnly config setting (true by default)


  • Added browserless ‘native’ client for CentOS 7 and Windows 7
  • Fixed relative paths for Server.LicensePath
  • Updated fonts, icons, and colors
  • Changed from Windows NSIS installer to MSI installer


  • Fixed “too many files open” error for generic stream video source


  • Improved error handling for disconnects during inactivity
  • Changed default idle user timeout to 2 hours


  • Fixed black winlogon screen for stream video source


  • Fixed screen size changing in Windows


  • Fixed handling of poor network connections
  • Windows installer preserves *.dat, *.lic files on update


  • Fixed blackscreen when using IE 11 over a VPN
  • Fixed systemd service status check


  • Fixed init script false-positive when license checkout fails
  • Fixed systemd service script
  • Reduced log output on license checkout retries


  • Added CPU-based (stream) video source option
  • Added idle user timeout (Server.IdleUserTimeout takes minutes. Disabled by default)
  • Added ability to update Server.Auth settings at runtime (except Server.Auth.Enabled)
  • Added ability to auto-select a video source
  • Added Flexera License Management
  • Added ability to specify license file with Server.LicenseFile config setting
  • Added ability to delay service start with Server.StartDelay config setting
  • Renamed Server.WebSocketServer.Secure to Server.Secure
  • Renamed Server.WebSocketServer.Port to Server.Port
  • Renamed Server.ServiceLogFile to Server.BootLogFile
  • Renamed debug0.txt to boot.log and debug1.txt to scyld-cloud-workstation.log
  • Changed Windows install directory to C:\Program Files\Penguin Computing\Scyld Cloud Workstation
  • Changed Windows service startup from Automatic to Delayed
  • Changed log messages
  • Fixed guests getting kicked out if one of multiple hosts signs out
  • Fixed handling of IPv6 addresses
  • Fixed guest toolbar being hidden while paused
  • Fixed duplication of guest alerts
  • Fixed guest video when starting out paused


  • Added support for CentOS 7 (requires LightDM / MATE desktop environment)
  • Added Floating UI
  • Added adjustable screen resolutions limits
  • Added Server.Video.MaxWidth and Server.Video.MaxHeight to config file
  • Updated QoS algorithm
  • Windows installer preserves *.crt, *.cer, *.pem, *.key, and *.der files on update
  • Set default max frame rates to 30
  • Fixed Firefox keyboard issue for remote Windows services


  • Increased send timeout values
  • Added Server.VideoSendTimeout, Server.DataSendTimeout, and Server.ReceiveTimeout to config file


  • Fixed QoS adaptive frame rate algorithm


  • Fixed IE11 fullscreen keyboard and scrollbars


  • Fixed unexpected multi-user client timeouts


  • Added keyboard and mouse sharing for collaboration
  • Added guest invites for collaboration
  • Added text paste from local clipboard support
  • Added remote desktop auto-lock on disconnect
  • Updated QoS algorithm
  • Updated user interface style
  • Updated default SSL ciphers
  • Compatible with v2.3 config file


  • Updated default SSL ciphers


  • Fixed Command/Windows key getting stuck
  • Fixed cursor disappearing during Windows UAC


  • Improved decode performance
  • Improved QoS responsiveness
  • Improved mouse scrolling. Ticks are now server-dependent
  • Added code authenticity check
  • Fixed OS X command key
  • Improved version number system
  • Fix for null cursor
  • Fix for missing HTML icons
  • Added support for 16x16 cursors in Windows
  • Improved web-page refresh


  • Added local cursor
  • Added basic QoS / dynamic frame rate updates
  • Simplified configuration file by relying more on defaults
  • Updated interface controls to be centered, sleeker
  • Updated default openSSL.server.cipherList string to include !RC4
  • Updated default openSSL.server.verificationMode to relaxed
  • Fixed cursor in Firefox Fullscreen
  • Fixed mouse wheel
  • Fixed screen crop
  • Added auto-lock (disabled by default)
  • Authentication screen can now be disabled in config
  • RPM installer preserves old config file by default


  • Added screen resolution change support (Windows, Linux)
  • ScyldCloudAuth “JSON Syntax Error” fix
  • Silent / Quiet Windows installer

Server Requirements

This section describes the hardware and software requirements for the workstation hosting the Scyld Cloud Workstation server.

Server OS

Scyld Cloud Workstation is supported and tested on the following 64-bit operating systems:

  • Windows 7, 8
  • CentOS 6, 7

Beta support is available for:

  • Ubuntu 12, 14, 16


There is a known graphics issue with GNOME Shell based systems (GNOME 3 and GDM) on machines that do not have an attached monitor. For these systems, MATE desktop environment and LightDM can be used as a workaround.

If you require other versions of Windows, RedHat, and Debian based flavors of Linux, please contact Penguin Computing for additional support.

Server Hardware

Scyld Cloud Workstation is supported on the following server hardware configurations:

Server-Side Recommended Minimum
CPU > Intel Core i5, Dual-Core > Intel Core i5, Dual-Core
Memory > 2 GB > 2 GB
GPU Any Any

Server NVIDIA Drivers (Optional)

Scyld Cloud Workstation supports NVIDIA GRID GPUs such as the NVIDIA GRID K2 and Tesla M60. Drivers that support the NVIDIA GRID SDK are required. The following combinations have been successfully tested with version 7.1.8:

OS NVIDIA Driver Release
Windows 7 347.88 354.99 369.49
CentOS 6 354.41 361.42


The following issues are known for NVIDIA device drivers in Linux:

  • 331.62: the remote mouse cursor is not hidden when the local mouse cursor is active.
  • 340.46: changing the screen resolution via the xrandr command halts video stream.
  • 367.35, 367.57: changing the screen resolution via the xrandr command halts video stream.

Server Screen Resolutions

The performance of the remote access is partly dependent on the server’s screen resolution and the client’s ability to process that resolution quickly.

Scyld Cloud Workstation allows system administrators to pick a maximum screen resolution width and height in the config file (disabled by default). If the user attempts to change the screen resolution above this setting, then the video scales down automatically. This can alleviate situations where users set the screen resolution so high that their client machine becomes unusuable.

For most users, we recommend a resolution of 1600x900. If you’d like to test higher screen resolutions, we recommend doing so with gradual increases.


Changing screen resolutions has two known issues:

  1. Multiple rapid resolution changes may lead to service instability. Changing the screen resolution more than 5 times over a few seconds may cause the service to restart or quit.

For more information about changing screen resolutions, see Change Screen Resolution.


OpenSSL is an open source implementation of the SSL and TLS protocols and must be installed on the server host. Most Linux distributions have this installed by default, but this should be downloaded and installed manually in Windows before you can install Scyld Cloud Workstation.

For Windows hosts, download the latest Win64 OpenSSL package (either full or light versions will work) from Shining Light Productions: https://slproweb.com/products/Win32OpenSSL.html


OpenSSL 1.0 is required and is supported through December 31, 2019. OpenSSL 1.1 is currently not supported with Scyld Cloud Workstation.

SSL Certificate

An SSL certificate signed by a trusted certificate authority is used to provide encryption and authentication for a client’s HTTPS connection to the Scyld Cloud Workstation web server. By default, Scyld Cloud Workstation comes with a self-signed SSL certificate and private key that should not be used in secure production environments.

For more information on generating SSL certificates, see Setup.

Client Requirements

This section describes the hardware and software requirements for the connecting client.

Client Hardware and Network

We recommend using clients with the following minimum specs.

Client-Side Recommended
CPU > Intel Core i5, Dual-Core
Memory > 2 GB
Network Bandwidth > 5.5 Mbps
Network Latency < 80 ms


Acceptable network latency is application dependent. For certain applications, users may find 150 ms to be acceptable. Performance may degrade if the client is running background applications that consume significant amounts of CPU time, memory, or network bandwidth.

Client Web Browsers

The following web browsers are supported and listed in order of performance:

  • Chrome 30+
  • FireFox 27-37, 39+
  • Internet Explorer 11+
  • Safari 7+


Chrome 30+ provides the best performance and is recommended.

These browsers by default enable TLS 1.2, WebGL and WebSocket features that are necessary for security and optimal Scyld Cloud Workstation performance. While WebSocket support is a hard requirement, Scyld Cloud Workstation is capable of running without WebGL support at reduced performance levels.

The following links can be used to determine if your browser supports necessary features for an optimal Scyld Cloud Workstation experience:

Browser Feature Test for Browser Support
Security Protocol TLS 1.2 https://www.ssllabs.com/ssltest/viewMyClient.html
WebGL https://get.webgl.org/
WebSockets http://websocketstest.com/


TLS 1.2 is the current standard used to secure HTTPS connections as of the writing of this document.