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System short freeze


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I have been experiencing an issue (for almost a year) that seeming randomly the system that is the primary for Synergy will freeze for 5 - 10 seconds when I am working on a secondary system.  It never freezes when I am working on the primary system.  This is very problematic as when the freeze occurs the mouse returns to the center of the primary systems screen 1.  If I am in the middle of editing a spreadsheet on system 2 randomly system 1 will freeze and the mouse moves back to system 1.  This is annoying and makes it hard to work on the other systems as I am constantly having to pull the mouse back to system 2 after system 1 returns to normal operation.

This only happens when Synergy is running.

System 1 - Windows 7 Ultimate, Synergy 2.012 beta

System 2 - Windows 10 Pro, Synergy 2.012 beta

I have reviewed the system logs and find no indication of why this is happening.  The system just stops for 5 - 10 seconds and then starts going again.

Thank you,





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  • 1 year later...

This has been happening to me basically since I bought the product 2021-01-18 as well. Recently I spent quite a few hours finally trying to figure out what is going on. Initially I thought something must be wrong with my primary system since it locks up completely every time this happens. I downloaded a program called "LatencyMon" that can measure how long the system spends in interrupt routines from drivers but these system freezes were never detected by it.


Eventually I saw in task manager that my last core shoots up to 100% usage during the few seconds while the system is locked up... This shouldn't normally make the whole system freeze though... But actually now that I started thinking about it more, the fans of my primary system also always spin up while the freeze is going on.


I switched the task manager from the performance tab to the process tab and sorted by CPU and waited for the next freeze. I noticed that synergys.exe was using about 1-2% as I moved the mouse heavily on the second system and eventually when it froze again I saw it much higher for a brief moment (during the freeze though the entire task manager locks up for a few seconds so it's hard to get an accurate reading). But after this I really started suspecting Symless Synergy as the culprit.


100% CPU usage, on just one of my 8 cores, that should not be freezing the entire system... What about process priorities? I went through the priorities of all the Synergy processes and lo and behold, the synergyd process is set to "Realtime". This is really dangerous, it means that the process runs on higher priority than mouse and keyboard input itself. This could absolutely be the cause why the whole system freezes up.
See this blog post from a Microsoft employee:



This means that if the synergyd process is using all the CPU waiting for input it will never get input because the input thread in windows runs on lower priority than synergy itself.


I have now instead set the priority of all synergy processes (synergy.exe, synergyd.exe, synergys.exe) to the lowest: "Low" on the primary system and I don't notice any difference in latency when moving the mouse but most importantly I have yet to see this freeze happening again. If it happens again then at least only synergy should freeze, not the entire primary system, but I suspect this might have fixed the freezing completely.

For now though I don't have a permanent solution for this since changing priorities will have to be done after each primary system restart or just restart of the Synergy processes. This seems like a bug in Synergy, it should probably not be using "Realtime" priority, "Normal" should work fine but perhaps "High" might be acceptable as well.

Edited by Arques
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I used to get maybe ~2-5 of these freezes per hour but now I've worked on the secondary PC for many hours without a single freeze.


I have also found a working permanent workaround for this issue that doesn't require manually changing priority every time the Synergy service restarts. By downloading and installing "BitSum Process Lasso", you can select all three synergy processes (synergy.exe, synergys.exe & synergyd.exe), right click and select "Priority class -> Always -> Idle (Lowest)".


To make sure that Process Lasso aggressively maintains the low priority on these you can go to the top menu "Options -> CPU -> CPU Priorities..." and check "More strictly enforce default priorities". This will make Process Lasso very quickly set the priority back in case the Synergy process restarts or tries to modify its own priority. Otherwise, if you change any settings in the Synergy GUI and click "Apply" that will restart the synergys.exe process with Realtime priority again and the freezes will start again.


Note that this is only valid for Windows. I have not tried Synergy on Linux but hopefully this is not even an issue on that platform.

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