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Congrats on all the research you did about how to make and use Symbol files! I would guess the program files are read only, because the system admin wants to protect them. But putting in the user directories should work just as well.
I think you are putting the files in the right place. Are they SVG files?
I thought I could look at some of the symbol files I've installed, to find out if there's some particular way the files should be made. But when I look at the SVG files for the symbol sets, they appear to be empty! I'm not sure what to make of that. Although I always like to say that my computer not-know-how is large
I found some symbol files in the program files though, and there the images appear. Looking at the XML Editor, I see that they are made using what I consider unusual elements. So instead of the id attribute's value of "path" or "rect" "g" (group), it's "use".
Here's how a path looks in XML Editor: <svg:path id="path1234">
They symbol object looks like this: <svg:use id="use1234">
Oh ok, I think I might have it figured out.....maybe. When you made the SVG symbol file, are they all paths still? Or did you convert to symbols in the Current Document?
If I can figure this out, maybe I'll write a tutorial. Because it's not entirely obvious how to do it. But these are the basics, as far as I can tell.
1 -- Draw the new symbol
2 -- Object menu > Symbols > Current Document
3 -- Click "Add symbol from current document" button, which is in the bottom-left corner of the symbol area in the Symbols dialog. Now you should see the new symbol in the Symbols dialog.
4 -- Save the file as SVG
5 -- In the file manager, copy that SVG file from wherever you saved it, and paste it into the user symbol directory
Now, when you open a new Inkscape file, and open the Symbols dialog, you'll see a new item in the Symbol Set dropdown menu, called Unnamed Symbols. If you click on that, you'll see the new symbol you created.
I haven't figured out how to name the individual symbols yet. Or how to name the symbol set, so that it shows up in the dropdown menu, with a name besides "Unnamed Symbols". But once I get those 2 things figured out, I'll try and write a tutorial.
I hope some of that will help. Let us know how it goes