How to determine if a process runs inside lxc/Docker?

Question

Is there any way to determine if a process (script) runs inside an lxc container (~ Docker runtime)? I know that some programs are able to detect whether they run inside a v

Answer 1

Check for all the solutions above in Python:

import os

def in_container():
    proc_1 = r'/proc/1/sched'

    if os.path.exists(proc_1):
        with open(proc_1, 'r') as fp:
            out = fp.read()
    else:
        out = ''

    checks = [
        'docker' in out,
        '/lxc/' in out,
        out.split(' ')[0] not in ('systemd', 'init',),
        os.path.exists('./dockerenv'),
        os.path.exists('/.dockerinit'),
        os.getenv('container') is not None
    ]
    return any(checks)


if __name__ == '__main__':
    print(in_container())

Proof of concept:

$ docker run --rm -it --mount type=bind,source=${PWD}/incontainer.py,target=/tmp/script.py python:3 python /tmp/script.py
True

Answer 2

Handy Python function to check if running in Docker:

def in_docker():
    """ Returns: True if running in a Docker container, else False """
    with open('/proc/1/cgroup', 'rt') as ifh:
        return 'docker' in ifh.read()

Answer 3

A concise way to check for docker in a bash script is:

#!/bin/bash
if grep docker /proc/1/cgroup -qa; then
   echo I'm running on docker.
fi

Answer 4

Maybe this do the trick:

if [ -z $(docker ps -q) ]; then
    echo "There is not process currently running"
else
    echo "There are processes running"
fi

Is that what you want? Hope it helps =)

Answer 5

In a docker container, entries /proc/self/cgroup are mounted to cgroups on the host.

e.g. in a container

# awk -F: '/cpuset/' /proc/self/cgroup
3:cpuset:/docker/22bd0c154fb4e0d1b6c748faf1f1a12116acc21ce287618a115ad2bea41256b3

whereas, the same on the host

$ awk -F: '/cpuset/' /proc/self/cgroup
3:cpuset:/

Using something in the shell for a low profile test

is_running_in_container() {
  awk -F: '/cpuset/ && $3 ~ /^\/$/{ c=1 } END { exit c }' /proc/self/cgroup
}

if is_running_in_container; then
  echo "Aye!! I'm in a container"
else 
  echo "Nay!! I'm not in a container"
fi

Answer 6

Docker is evolving day by day, so we can't say for sure if they are going to keep .dockerenv .dockerinit in the future.

In most of the Linux flavours init is the first process to start. But in case of containers this is not true.

#!/bin/bash
if ps -p1|grep -q init;then  
  echo "non-docker" 
else 
  echo "docker" 
fi