Written for Synergy 3 (v3.7.2), checked 3 October 2026.
Click Yes. Synergy 3 stops the other program and starts sharing your keyboard and mouse. Only one keyboard and mouse sharing app can run on a computer at a time, because they all use the same network port.
Which message did you see?
- Already running: another keyboard and mouse sharing app, such as Barrier or Input Leap, is running. To stop this coming back, quit that app or remove it from your startup apps.
- Legacy core running: an old version of Synergy 1 is still running. To stop this coming back, quit it or uninstall it.
- Core already running: another copy of Synergy 3's own sharing process is running, for example left over after a crash. Click Yes to replace it.
Click Cancel to leave the other program running; Synergy 3 can't share your keyboard and mouse until it stops.
If the message keeps coming back after you click Yes, restart the computer. If that doesn't help, send us a diagnostic report: How to get diagnostic info?