Containers are provided by host kernel cgroups and namespaces, therefore the kernel implements attach (exec) operation which is practically running a new proces

Containers are provided by host kernel cgroups and namespaces, therefore the kernel implements attach (exec) operation which is practically running a new proces (e.g. bash) in a cgroup (container). Virtual Machines are provided by software or hardware emulation which run separate guest OS with own kernel. There is no standard way for a host to let you run any process and interact with its stdio inside guest OS because the host simply is not aware what you exactly run inside. The solution is to have an agreed connectivity standard both on the guest and the host. The guest can provide SSH server, telnet server serial terminal, irc bot or some other kind of control capability. Then of course host needs a tooling too, e.g. SSH client.