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Nick Bolton edited this page Jul 16, 2024 · 1 revision

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Motivation

As a platform for software-based input sharing, Synergy currently requires the use of locally connected displays. This means that each physical (not locally virtualized) member of the Synergy network requires the deskspace of at least one monitor.

This limitation can be overcome by some method of switching the input being given to a display. In general, this would be done manually, with either a physical input switcher or the monitor's built in controls. However, hardware switches can be clunky and expensive, and reaching out to navigate your monitor's menus every minute can be frustrating.

For some, VNC would provide an acceptable solution, but its video performance, understandably, leaves a lot to be desired. Instead, a software-based method of switching video among local boxes, coupled with Synergy's very speedy input sharing, can be used to create what is effectively a software-based KVM switch.

General method

Every platform currently supported by Synergy provides methods of turning video outputs on and off at will from the command line.

These are:

  • XRandR for Linux (or probably anything that uses X as basis for a desktop environment)
  • Pmset for OS X
  • NirCmd for Windows (Untested)
We can use these tools to write scripts that will appropriately schedule the toggling of video outputs among the locally attached boxes, so as to provide the appearance of a hardware KVM switch. Existing OS and Synergy functionality can be used to enhance the effect, with globalized keybindings to toggle inputs and relocate focus, clipboard sharing, and flawless inter-screen mouse transitions.

Linux and macOS

I successfully use the following script with a Linux server and Mac OS X client. I suspect that something similar will work with the majority of configurations, but I don't have the capacity for further testing right now.

This script can be seen in action around 50 seconds into this video.

Potentially relevant parts of the setup shown are as follows:

OS GPU Connected Monitors
Arch Linux Radeon HD 7700 Acer V2223W (DFP5) and Acer AL2223W (DFP6)
Mac OS X Lion (10.7.5) NVIDIA GeForce 9400 Acer AL2223W (DFP6)

Arch is constantly displayed on DFP5, and I toggle between Arch and OS X on DFP6.

I put the following shell script on the Linux server. Please feel free to improve it: 

#!/bin/bash

CLIENT_MAC=00:00:00:00:00:00
CLIENT_IP=192.168.1.XXX # a static IP for the client
CLIENT_USER=user # we use this to login to the client through ssh

# wake up the client. Only necessary if you want to let it sleep when idle.
wol $CLIENT_MAC 

TOGGLE=$HOME/.display_toggler
if [ ! -e $TOGGLE ]; then 
	touch $TOGGLE
	xrandr --output DFP5 --off &&
	ssh -ft $CLIENT_USER@$CLIENT_IP "sudo pmset force -a displaysleep 0"
else
	rm $TOGGLE
	MAGIC_NUMBER=2147483648 # gives pmset a seizure, causing the video output to terminate 
	xrandr --output DFP5 --auto --right-of DFP6 &&
	ssh -ft $CLIENT_USER@$CLIENT_IP "sudo pmset force -a displaysleep $MAGIC_NUMBER"
fi

# the host appears to have lost or gained a monitor, so we need to inform Synergy of this
sudo /etc/rc.d/synergys restart

I use the WM on my Synergy host to map a keyboard shortcut to the toggle_display.sh script. Synergy is configured, using keystrokes, to always forward this input event to the host, so that the script on the host can be triggered from anywhere. This configuration also requires that you've shared ssh keys between your server and client, and that both your local and remote users are passwordless sudoers or root, because pmset won't work without root.

Problems

  • On at least some versions of OS X, you have to fiddle around if you want to let it sleep in this configuration. The darkwake=no option worked for me.
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