/etc/portage/make.conf

Global custom settings for portage, see

Variables
There are many variables available in make.conf, and as such, only the most commonly used are explained in detail here. For more information, and the full list of variables, consult the make.conf manpage.

CFLAGS / CXXFLAGS
Compilation flags.

CHOST
Compiler. Don't change this lightly. See http://www.gentoo.org/doc/en/change-chost.xml

GENTOO_MIRRORS
Mirror locations

INPUT_DEVICES
Input devices

LINGUAS
Languages

MAKEOPTS
Makefile opts

PORTDIR_OVERLAY
Local overlays

USE
Use flags

VIDEO_CARDS
Video cards

External Resources

 * http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?part=2&chap=3
 * http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?part=3&chap=2
 * http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?part=3&chap=6