How to check if a process is running inside docker container?

Question

[Updated1] I have a shell which will change TCP kernel parameters in some functions, but now I need to make this shell run in Docker container, that means, the shell need to know it is running inside a container and stop configuring the kernel.

Now I'm not sure how to achieve that, here is the contents of /proc/self/cgroup inside the container:

9:hugetlb:/ 8:perf_event:/ 7:blkio:/ 6:freezer:/ 5:devices:/ 4:memory:/ 3:cpuacct:/ 2:cpu:/docker/25ef774c390558ad8c4e9a8590b6a1956231aae404d6a7aba4dde320ff569b8b 1:cpuset:/ 

Any flags above can I use to figure out if this process is running inside a container?

[Updated2]: I have also noticed Determining if a process runs inside lxc/Docker, but it seems not working in this case, the content in /proc/1/cgroup of my container is:

8:perf_event:/ 7:blkio:/ 6:freezer:/ 5:devices:/ 4:memory:/ 3:cpuacct:/ 2:cpu:/docker/25ef774c390558ad8c4e9a8590b6a1956231aae404d6a7aba4dde320ff569b8b 1:cpuset:/ 

No /lxc/containerid

Answer 1

Docker creates .dockerenv and .dockerinit (removed in v1.11) files at the top of the container's directory tree so you might want to check if those exist.

Something like this should work.

#!/bin/bash if [ -f /.dockerenv ]; then     echo "I'm inside matrix ;("; else     echo "I'm living in real world!"; fi 

Answer 2

To check inside a Docker container if you are inside a Docker container or not can be done via /proc/1/cgroup. As this post suggests you can to the following:

Outside a docker container all entries in /proc/1/cgroup end on / as you can see here:

vagrant@ubuntu-13:~$ cat /proc/1/cgroup 11:name=systemd:/ 10:hugetlb:/ 9:perf_event:/ 8:blkio:/ 7:freezer:/ 6:devices:/ 5:memory:/ 4:cpuacct:/ 3:cpu:/ 2:cpuset:/ 

Inside a Docker container some of the control groups will belong to Docker (or LXC):

vagrant@ubuntu-13:~$ docker run busybox cat /proc/1/cgroup 11:name=systemd:/ 10:hugetlb:/ 9:perf_event:/ 8:blkio:/ 7:freezer:/ 6:devices:/docker/3601745b3bd54d9780436faa5f0e4f72bb46231663bb99a6bb892764917832c2 5:memory:/ 4:cpuacct:/ 3:cpu:/docker/3601745b3bd54d9780436faa5f0e4f72bb46231663bb99a6bb892764917832c2 2:cpuset:/