The Problem is : Equality for a circle / arc means same radius and center point, not same start/end points. Same is for a line or the like..it has teh same length , but still can be anywhere in space. Set the 2 intersect points to the lines to be constrained vertically and all is well.. Harry I'm n...

Now again push/pull on the horizontal lines and the circle center (with long movements); you will notice the behavior is not as nice as above. Pulling and pushing the Horizontal lines or (e.g. the center of) the circle produces "positions" similar to this: Screenshot from 2021-04-04 11-25...

Straight to the issue: Open FreeCAD, create a new document, create a Part, Body and start a Sketch. Create a rectangle to the left of the Origin, make it 10mm high, attach e.g. lower right corner to the Origin. Create a Circle, set radius to be 10mm. Move it to make one third of it cover the left en...

Sketcher's geometric elements toolbar is divided into three sections: 1) Geometric primitives: point, line, arc, circle, conics, B-spline (yes, in this context I would call them primitive). 2) Shortcuts for creating multiple of the primitives listed in point 1): polyline, rectangle, polygons, slot ...

I suspect this is Somehow related:
https://askubuntu.com/a/1301404/289138
... it appeared somewhere in the same commotion.

Thanks, problem solved.

Had nvidia driver version 455 (from Ubuntu additional drivers) installed since a few days back...
Backing off to version 450 solved the issue.

Please tell what made you think it was the OpenGL/Gfx driver?

Launch from bash... with a filename. $ freecad-daily HN-Logo.FCStd FreeCAD 0.19, Libs: 0.19R © Juergen Riegel, Werner Mayer, Yorik van Havre and others 2001-2020 FreeCAD is free and open-source software licensed under the terms of LGPL2+ license. FreeCAD wouldn't be possible without FreeCAD communit...

Right, ;-) Open freecad, attempt to open the file. {lengthy wait for anything to happen here} The sigseg happens immediately at click on the close-window button. No sigseg on launch and immediate close. Nothing special in the Python console. Open file from Menu or toolbar button makes no difference.

OS: Ubuntu 20.04.1 LTS (ubuntu:GNOME/ubuntu) Word size of OS: 64-bit Word size of FreeCAD: 64-bit Version: 0.19. Build type: Release Branch: unknown Hash: b920bbf73a594881a807f7d7cf056fbc1e99f53a Python version: 3.8.5 Qt version: 5.12.8 Coin version: 4.0.0 OCC version: 7.3.0 Locale: English/United S...

The "FAQ" link in https://forum.freecadweb.org/viewtopic.php?f=3&t=30573 is vierd,
with FF 83 on Ubuntu 20.04 i get a "download" dialog when clicking it.

I assume it should instead go to
https://wiki.freecadweb.org/Frequently_asked_questions