/usr/local status among commonly used software

DBus

In the NEWS file in the tarball, you can see that from version 1.0 RC 3 (0.95) the session directories are /usr/local/share/dbus-1/services, /usr/share/dbus-1/services, and $HOME/.local/share/dbus-1/services.

Gnome

glib's g_get_system_data_dirs() has been returning /usr/local/share:/usr/share for a while, which is why/how recent versions of Gnome work properly with fd.o base directory specs.

pkg-config

pkg-config uses a default search path of $prefix/local/pkgconfig:$prefix/share/pkgconfig (yuck!) unless you ./configure --with-pc-path. A patch has been submitted to unconditionally search /usr/lib/pkgconfig:/usr/share/pkgconfig:/usr/local/lib/pkgconfig:/usr/local/share/pkgconfig and is expected to be accepted (http://lists.freedesktop.org/archives/pkg-config/2007-July/000208.html).

fontconfig

Font search paths are read from fonts.conf, which is generated from fonts.conf.in at configure time from (too many) parameters to ./configure. By default, you get /usr/share/fonts and ~/.fonts. Debian-based distributions seem to add /usr/local/share/fonts and at least CentOS doesn't. The argument is that it doesn't matter that /usr/local/share/fonts is not there, because applications probably shouldn't install custom fonts system-wide (http://lists.freedesktop.org/archives/fontconfig/2007-August/002656.html).

gcc

GCC 4.0 seems to find header files in /usr/local/include and links with libraries in /usr/local/lib.

man

man's default search path includes /usr/local/share/man/...

GNU info

"strace info nonExistingPage 2>log.txt" and "less log.txt", it looks in many places, among them /usr/local/share/info. Info pages in that directory are found. Version 4.6 and later look there, earlier versions might too (check info/filesys.h in the source tree).

ld-linux

GNU libc's ld-linux, the run-time dynamic linker, seems to get the search path through some bizarre little Perl script if I recall correctly, and it doesn't look in /usr/local/lib by default or on any distro. It's reported to Ubuntu at https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/73429 but ideally it should be fixed in libc itself.