Wiki - Multiple Instances



Explain the caveats and workarounds to running QZ Tray on a multi-user workstation.


QZ Tray is a singleton application and it cannot support multiple simultaneous instances on the same machine because QZ Tray uses a localhost websocket connection (wss://) from the browser to a single port on the PC. If a second instance of QZ Tray were allowed, the websocket would only ever succeed to the first available port, rendering the second instance useless.

Some options to help with this limitation:


Since QZ Tray will start automatically with the computer, this singleton limitation can pose a problem on a shared workstation. By default, QZ Tray will attempt to start automatically upon login however if another user is running QZ Tray, it will detect the other instance and quietly shutdown. This is usually observed by the following behavior:

"QZ Tray icon disappears from the system tray"

"When I double-click on the QZ Tray icon, it shows up for a second and then goes away"

"There's link on the web page to start QZ Tray (e.g. qz:launch but it doesn't work if someone else is signed onto the computer"

Stealing Instance

Since 2.1.4, QZ Tray supports stealing another instance, which can be helpful on shared workstations. There are several ways to toggle this behavior on:

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