Perhaps my blood sugar is just too low.

Seeing this type of error in Gentoo?

* ERROR: sys-apps/portage-2.1.5.5 failed.
 * Call stack:
 * ebuild.sh, line 1792: Called dyn_unpack
 * ebuild.sh, line 686: Called die
 * The specific snippet of code:
 * touch "${PORTAGE_BUILDDIR}/.unpacked" || die "IO Failure -- Failed 'touch .unpacked' in ${PORTAGE_BUILDDIR}"
 * The die message:
 * IO Failure -- Failed 'touch .unpacked' in /var/tmp/portage/sys-apps/portage-2.1.5.5
Apparently touch no longer works in my distro. Can’t build anything.
http://bugs.gentoo.org/show_bug.cgi?id=224483
It appears my kernel (2.6.21-gentoo-r3) is out of date compared with my linux-headers (2.6.25-r3) package and this screws up the latest version of touch which comes with coreutils. Update your kernel. But touch doesn’t work, so you need to go get an old version:
wget http://tinderbox.dev.gentoo.org/default-linux/x86/sys-apps/coreutils-6.10-r2.tbz2
mv coreutils-6.10-r2.tbz2 /usr/portage/distfiles/
emerge -k =sys-apps/coreutils-6.10-r2
Now go update your kernel.