Well, here's additional info about the app. Because it accesses GPIO, it needs to be run with sudo, unless I can figure out the right priviledge to run it as normal user. So, maybe the sudo causes it to not use the regular user's .gtkrc-2.0 file. I tried to put these files in the /root directory, but that didn't seem to have an effect. Gtk does not permit you to make the program owned by root:root and set for u+s file permissions.
I have split another app into two parts and have them communicate via rpc, but that was quite complicated.

Another issue is that the system seems to have at least part of gtk3.0 installed, In /usr/lib, I see such files as libseed-gtk3.so.0 and seed-gtk3
but I don't see libgtk-3.0 (or libgtk-2.0 either) so I must be looking in the wrong place.

I do not have strace on this system, or at least, don't know how to use it.
This is a Beagle Board running :
3.2.19-x13 #1 SMP Tue Jun 5 08:48:31 UTC 2012 armv7l armv7l armv7l GNU/Linux

At one point I did get it to change the fonts of the toolbar in emacs, but now that is not happening. I think it was one of the .gtkrc-3.0 files that did that. I'm guessing that the font I am calling out with gtk-font-name = is the wrong syntax. Can you suggest how to format what you get with fc-list to make a good .gtkrc-2.0 file?
Here's what fc-list gives :

DejaVu Sans:style=Bold
DejaVu Sans:style=Book
DejaVu Sans Mono:style=Book
DejaVu Sans Mono:style=Bold
DejaVu Serif:style=Book
DejaVu Serif:style=Bold
Thanks much for your help so far!
Jon

Try putting in /usr/share/gtk-2.0/gtkrc

strace would make debugging this problem trivial.
Ed

Astonishingly, this did nothing. I created files /usr/share/gtk-2.0/gtkrc and .gtkrc with gtk-font-name = "DejaVu Sans 32"
in them, and there is no change! I also put the same files under /usr/share/gtk-3.0, still no difference.
OK, one thing to note is that the embedded system is NOT running an X windows server. I connect to it either with a MS Windows system with putty and xming, or a Linux system that IS running X Windows. Maybe the issue is all on those X server systems.
The system does have :/usr/lib/arm-linux-gnueabihf/libgtk-3-0:
total 64
drwxr-xr-x 2 root root 4096 Jun 18 2012 .
drwxr-xr-x 35 root root 24576 Jun 18 2012 ..
-rwxr-xr-x 1 root root 9808 May 21 2012 gtk-query-immodules-3.0
-rwxr-xr-x 1 root root 22556 May 21 2012 gtk-update-icon-cache-3.0
but I'm not sure that is the whole gtk-3.0 library.
There is also :
usr/lib/arm-linux-gnueabihf/libgtk-3.so.0.400.2 which is a 3 mb file, so it looks like gtk-3 is available. I just have to
hack the Makefile to link to it.

OK, so now I am trying to build the app with gtk-3.0
Previously, I had this in the Makefile:
COMMONSW = -c -D__unix__ `pkg-config --cflags --libs gtk+-2.0 libglade-2.0` -export-dynamic
OPTSW = -g $(COMMONSW)
LDFLAGS = -Wall -g `pkg-config --cflags --libs gtk+-2.0 libglade-2.0` -export-dynamic


CC = gcc
COMMONSW = -c -D__unix__ `pkg-config --cflags --libs gtk-3.0 libglade-2.0` -export-dynamic
OPTSW = -g $(COMMONSW)
LDFLAGS = -Wall -g `pkg-config --cflags --libs gtk-3 libglade-2.0` -export-dynamic

PROGOBJS= scdrvr.o scaler.o

all : Program

Program: $(PROGOBJS)
gcc -o scaler $(PROGOBJS) $(LDFLAGS)

scaler.o: scaler.c
$(CC) $(OPTSW) $<

scdrvr.o: scdrvr.c
$(CC) $(OPTSW) $<

clean:
rm -f *.o
[/code]
But, I get this error:
Package gtk-3.0 was not found in the pkg-config search path.
OK, so this gtk+-2.0 syntax must be something special for make, when I put in gtk+-3.0 it started pulling in the gtk 3.0 files, but then I run into lots of version compatabilty errors. Looks like a HUGE mess. I'm not sure I can handle that big a conversion.
Any suggestions to make it easier?
Thanks,
Jon

OK, now I got it to compile and link with gtk3.0, but I get :

/home/elson/scaler3/scaler.c:246: undefined reference to `gtk_entry_set_attributes'

Here's the line from the c source :

gtk_entry_set_attributes(Pscaler[0], attr);

IS this syntax wrong?
Thanks,
Jon

Well, here's some new info, now that the app is linked with gtk3.0 :
scaler:884): Gtk-WARNING **: Failed to parse /root/.config/gtk-3.0/settings.ini: Key file contains line 'style "user-font"' which is not a key-value pair, group, or comment

(scaler:884): Gtk-WARNING **: Theme parsing error: gtk.css:6:17: Junk at end of value

(scaler:884): Gtk-WARNING **: Theme parsing error: gtk-keys.css:4:13: Expected a valid selector

And, here is the contents of /root/.config/gtk-3.0/settings.ini :

style "user-font"
{
font_name="DejaVu Sans 24"
}
widget_class "*" style "user-font"

gtk-theme-name="QtCurve"
gtk-font-name="DejaVu Sans 24"

Anybody see what I did wrong there?
Thanks,
Jon

New, I have this in /root/.config/gtk-3.0/settings.ini :
[Settings]
gtk-application-prefer-dark-theme = false
gtk-theme-name = Zukitwo
gtk-fallback-icon-theme = gnome
gtk-icon-theme-name = Faenza-Dark
gtk-font-name = DejaVu Sans 36
And, it gets rid of the first 2 warning messages, but the 3rd one about gtk-keys.css remains. So far, I have not found this file.
But, it still doesn't change the font size of the app.
Thanks,

Jon

Using [code]..[/code] tags would make all these posts easier to read...

Jon - I think if I came back to this thread in a day, you will have it figured out.

Yes, the GTK 2 gtkrc and the GTK 3 settings.ini have different syntax. I believe that "style" and "widget_class" are not valid in the latter.

The GTK 3 gtk.css has a third syntax.

You can dump the settings by running gtk-query-settings.
Ed

Wow, gtk-query-settings sure give a lot of info on my Ubuntu desktop system, but it is not available on the embedded system. Darn!

Well, I have not solved anything yet. To make it simpler, I am running the app logged directly into root, so as to avoid any effects that sudo might cause. I have put this is the /root/.config/gtk-3.0/settings.ini file :
[Settings]
gtk-font-name = DejaVu Sans 36
I don't get any error on this, but it seems to have no effect on anything. If I do botch the syntax, I do get an error, but if I put gibberish in the font name, there is no error.
If I could just set all displayed fonts to be larger, that would solve the issue, this embedded computer is just to run one program and serve a GUI over ssh.
The program gsettings DOES exist there, but I am still trying to find where the default font/size is set.
Thanks for any hints,
Jon