Up until Linux 3.8/3.9 the shutdown() syscall was not container aware and hence shutting down from inside a container would shutdown a host
It has since been fixed and attached to the 'PID' namespace meaning that all processes in the PID namespace get shutdown in the same manner as the host calling shutdown() (ie init gets a specific signal, userspace processes get signaled as well)
It has since been fixed and attached to the 'PID' namespace meaning that all processes in the PID namespace get shutdown in the same manner as the host calling shutdown() (ie init gets a specific signal, userspace processes get signaled as well)