Note that these fail when run in a Docker container because a) the
current container's locale is not completely set, and b) getlogin()
returns null with ENOENT since /var/run/utmp is being mapped to the
host, and thus denied access from within the container.
The container needs the locale set and its own /run/utmp, see
https://lists.linuxcontainers.org/pipermail/lxc-users/2011-July/002374.html