bug#19568: 24.3; not documented: Which system settings affect the choice of the default font by an uncustomized Emacs 24?

[Ivan Zakharyaschev <imz@altlinux.org>]

My situation and the issue are like the ones in
<http://lists.gnu.org/archive/html/help-gnu-emacs/2012-06/msg00183.html>
(Florian Lindner):

> after the recent upgrade to emacs 24.x (...) my font size
> is too large (one times C-x C-minus corrects it temporarily for the
> buffer). The menu font size is fine, the rest (buffer, mode line,
> minibuffer is too large). I've read about the various ways to set the
> font size.
>
> **Is there a specific reason why the font size has increased after the
> update? And thus a global way to correct it?**

So, even having read about all the ways to set a font in Emacs, I
haven't found an answer which would explain the difference in font
size between an uncustomized Emacs 23.x and Emacs 24.y.

Probably, it's as in the follow-up answer (Tassilo Horn):

> Emacs 24 adds support for gconf and gsettings, so it'll pick whatever
> monospace font and sizes you have set as the default in your system
> settings

I'd like to know the place these settings are stored, and to tweak
them (so that not only Emacs, but perhaps other similarly behaving
programs would get my font settings).

I'm especially interested in making the default font size smaller again.

Unforunately, [in the Emacs
manual](http://www.gnu.org/software/emacs/manual/html_node/emacs/Fonts.html)
it is not documented which system settings affect the choice of the
default font by an uncustomized Emacs 24.

I believe this is an important information for an Emacs user and
should be present in the manual.

In GNU Emacs 24.3.1 (x86_64-alt-linux-gnu, GTK+ Version 3.8.1)
 of 2013-04-20 on localhost.localdomain
Windowing system distributor `The X.Org Foundation', version 11.0.11405000
System Description:	Simply Linux 7.0.4  (Dory)

Configured using:
 `configure '--build=x86_64-alt-linux' '--host=x86_64-alt-linux'
 '--prefix=/usr' '--exec-prefix=/usr' '--bindir=/usr/bin'
 '--sbindir=/usr/sbin' '--sysconfdir=/etc' '--datadir=/usr/share'
 '--includedir=/usr/include' '--libdir=/usr/lib64'
 '--libexecdir=/usr/lib' '--localstatedir=/var/lib'
 '--sharedstatedir=/var/lib' '--mandir=/usr/share/man'
 '--infodir=/usr/share/info' '--disable-dependency-tracking'
 '--without-included-gettext' '--sharedstatedir=/var' '--with-pop'
 '--with-x-toolkit=gtk3' '--with-png' '--with-jpeg' '--with-xpm'
 '--with-gif' '--with-tiff' '--with-gpm' '--enable-font-backend'
 '--with-freetype' '--with-xft' '--with-dbus' '--with-rsvg'
 '--without-compress-info' '--with-wide-int'
 '--enable-link-time-optimization' 'build_alias=x86_64-alt-linux'
 'host_alias=x86_64-alt-linux' 'CFLAGS=-pipe -Wall -g -O2''

Important settings:
  value of $LANG: ru_RU.UTF-8
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Text

Minor modes in effect:
  flyspell-mode: t
  shell-dirtrack-mode: t
  show-paren-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  auto-fill-function: do-auto-fill
  transient-mark-mode: t

Recent input:
M-x e m a <tab> <tab> <backspace> <backspace> <backspace>
<backspace> <backspace> <backspace> r e p o <tab> <tab>
r t - e <tab> <return> M-x <up> <return>

Recent messages:
Loading /etc/emacs/site-start.d/10keys.el (source)...done
Loading /etc/emacs/site-start.d/10mouse.el (source)...done
Loading /etc/emacs/site-start.d/10selection.el (source)...
Error while loading /etc/emacs/site-start.d/10selection.el
Loading /etc/emacs/site-start.d/git.el (source)...done
Loading /etc/emacs/site-start.d/rus-win-keyboard.el (source)...done
Loading /home/imz/.emacs.d/site-start.d/tramp-proxy.el (source)...done
Starting new Ispell process [/usr/bin/aspell::default] ...
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list... [2 times]
byte-code: Cannot open load file: rfc2047

Load-path shadows:
/usr/share/emacs/24.3/lisp/mouse-sel hides
/usr/share/emacs/24.3/lisp/obsolete/mouse-sel

Features:
(shadow sort gnus-util mail-extr emacsbug message rfc822 mml mml-sec
mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils
mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils flyspell ispell tramp tramp-compat password-cache
tramp-loaddefs shell pcomplete comint ansi-color format-spec advice
help-fns cl-lib advice-preload quail help-mode git log-edit easymenu
easy-mmode ring pcvs-util add-log ewoc saveplace paren time-date
cyril-util tooltip ediff-hook vc-hooks lisp-float-type mwheel x-win
x-dnd tool-bar dnd fontset image regexp-opt fringe tabulated-list
newcomment lisp-mode register page menu-bar rfn-eshadow timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core frame cham
georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese hebrew greek romanian slovak czech european ethiopic
indian cyrillic chinese case-table epa-hook jka-cmpr-hook help simple
abbrev minibuffer loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote make-network-process
dbusbind dynamic-setting system-font-setting font-render-setting
move-toolbar gtk x-toolkit x multi-tty emacs)
--text follows this line--


-- 
Ivan