Common Problems

"Grbl has not finished booting."

This happens when UGS connects to a serial port and does not receive the GRBL startup string. Typically this is caused by a configuration problem and can be solved by one of the following:

  1. Check the baud rate is 115200, or 9600 for very old versions of grbl.
  2. Make sure you are connecting to the correct port.
  3. Make sure you have installed any drivers required for your controller.
  4. Make sure GRBL is properly flashed on your controller.

Gcode program stopped working

The UGS Parser has a configurable list of rules to skip certain patterns, these rules are typically added by a Yes/No dialog asking if you would like to skip the erroneous commands in the future. Sometimes GRBL will get into an ALARM state and there will be lots of these popups which should not be skipped in the future.


Skipping good commands may lead to broken gcode. Those rules should be removed from the gcode processor by going into the controller options.

In UGS Classic the option is in Settings > Gcode Processor Configuration.

In UGS Platform the option is under Preferences... > UGS > Controller Options.

For both, you need to uncheck or remove the invalid settings in the bottom list:


Platform Specific Issues

Toolbars or Windows don't appear.

This usually happens if you try running the platform without the required version of Java. The user cache is initialized but some objects become corrupt and initialization fails in the future even after upgrading Java.

This can be fixed by clearing out the user cache directory which can be found on the UGS "About" screen seen in the image below.



Property Files


Occasionally it is useful to attach some of these property files to bug reports to help with reproducing a problem.

Classic UGS properties are stored in your home directory, which changes based on the operating system being used: windows: /home/user/ugs mac: ~/Library/Preferences/ugs * linux: ~/ugs

Files include UniversalGcodeSender.json which contain different settings, and a firmware_config directory which contains several configurations for different firmwares and testing profiles.


The platform version of UGS contains additional property files automatically created by the NetBeans Platform framework being used. These files are also contained in various locations based on the operating system being used. You can find the exact locations of these files in the About / Help menu (See screenshot above).

It is sometimes necessary to clear out these properties between major feature updates.

Operating System Compatibility Problems

Linux: Non Reparenting Window Managers

There are a number of window managers which are "non reparenting", this causes some problems with Java.

Some details about this problem can be seen here.

Use the _JAVA_AWT_WM_NONREPARENTING environment property to fix the problem: