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

Issue

[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

Solution

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:/

Answered By - Thomas Uhrig

Answer Checked By - Terry (WPSolving Volunteer)