They say, If you run SSHD in your Docker containers, you're doing it wrong. But sometime it is useful to log into Docker contain to do some checking or run some debug tools. Maybe it won't need to be SSH, Docker's exec command will suit this kind of senarios. Anyway we are trying to get into Docker containers to do something. In my case, I want to figure out what kind of external calls are maken by PHP-FPM by using strace.