If you look at the clientlauncher.log file in ~/.ignition/clientlauncher-data you can see the line it uses to actually launch a client:
INFO [ClientLauncherFrame ] [09:09:13,441]: Starting Java with the following parameters:nohup java -classpath /home/kevin/.ignition/clientlauncher-data/launchclient.jar -Djavaws.sr.gateway.addr.0=localhost:8088/main -Djavaws.sr.scope=D -Djavaws.sr.launchts=1552406951131 -Djavaws.sr.main=com.inductiveautomation.ignition.designer.DesignerStartupHook -Xms64M -Xmx512M -XX:MaxPermSize=128m -Dsun.java2d.d3d=false com.inductiveautomation.ignition.client.launch.BootstrapSwing &
You can copy/paste that into a terminal to launch one just the same.
You’d need a cached copy of launchclient.jar already though…