Hi.
I am using the JLinkRTTViewer in Ubuntu 19.10.
Part of the text in messages is displayed in black on a black background. If double-click on this text, you can see that it is there (the text is highlighted in blue on the picture)
At the same time, if I use a virtual machine with windows 10, then everything is displayed without problems. The same firmware, the same J-Link.


I attach screenshots of the JLinkRTTViewer from Ubuntu, and from Windows (here you can see that the lines end with numbers)

JLinkRTTLogger (ubuntu), save data without any problem.

What could be the problem?

I updated the version to 6.60a, but the problem remained. I have had this problem for a long time, with different versions of the Jlink.

I also use Ozone in Ubuntu, there are no problems with RTT text.

Maybe I can provide you some more information about the system or libraries used?

Oh sure.
For the test, I made a simple project on a nucleo H743.
Built-in ST-Link converted to J-Link. Without problems, it is displayed in Ozone (ubuntu) and JLinkRTTViewer (win10), but part of the text in JLinkRTTViewer (ubuntu 19.10) missing.

I did a small test: I download the ubuntu 19.10 ISO image and launched it in a virtual machine in live mode (without installation).
No system update, just install two lib* packets for jlink .deb package dependencies. Install JLink 6.60a. (deb, x64).
The lines look the same as mine, in the installed system - the numbers at the end of the line are black on black.