for building binaries that run everywhere, we need to love old stuff like centos6,
because it has the oldest glibc version which we want to support.
use 768MB for 64bit machines (not 512)
there's a problem with the shell:
- either it is no login shell, then e.g. PKG_PATH is not set (sh)
- or it is not found (no bash here)
- or it is not compatible enough (csh)
depending on what shell is configured, one or the other vagrant mode / feature
does not work.
