By default ccache stores its files in /root/.ccache when run as root. Since most emerge daily work is done as root and doc's suggested size for cache is 2 gigabyte, /root/.ccache will fill up at the first emerge involving a lot of compilation. On my system /root is as small as 500 mb cause it's not supposed to store too much stuff and i believe portage's ccache, which are not root personal files, should go somewhere under var. my is my temp fix: $ cat /etc/portage/bashrc export CCACHE_DIR=/var/ccache
You could set that in make.conf. Read make.conf.example.
i know i can change ccache behavior by myself and, if you read my post, i did it. But this doesn't fix the fact by default people are given settings not compliant to FHS. cache files generated by ccache are variable data related to the state of the application, hence should go to /var/, cache, lib or whatever.