Detect whether script running inside docker container

Question

How can a script detect whether it is running inside a container?

#!/bin/sh
if [ ... ]; then                 # ?
  echo 'running in container'
else
  echo 'running on host'
fi

Answer 1

This is one way with bash :

#!/bin/bash

in_docker(){
    local cgroup=/proc/self/cgroup
    test -f $cgroup && [[ "$(<$cgroup)" = *:cpuset:/docker/* ]]
}

if in_docker; then
  echo 'running in container'
else
  echo 'running on host'
fi

You need to convert to sh syntax if you don't have bash in your container.