How to determine if a process runs inside lxc/Dock

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 virtual machine, is something similar available for lxc/docker?

Answer 1

We use the proc's sched (/proc/$PID/sched) to extract the PID of the process. The process's PID inside the container will differ then it's PID on the host (a non-container system).

For example, the output of /proc/1/sched on a container will return:

root@33044d65037c:~# cat /proc/1/sched | head -n 1
bash (5276, #threads: 1)

While on a non-container host:

$ cat /proc/1/sched  | head -n 1
init (1, #threads: 1)

This helps to differentiate if you are in a container or not.