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

Answer 1

We needed to exclude processes running in containers, but instead of checking for just docker cgroups we decided to compare /proc//ns/pid to the init system at /proc/1/ns/pid. Example:

pid=$(ps ax | grep "[r]edis-server \*:6379" | awk '{print $1}')
if [ $(readlink "/proc/$pid/ns/pid") == $(readlink /proc/1/ns/pid) ]; then
   echo "pid $pid is the same namespace as init system"
else
   echo "pid $pid is in a different namespace as init system"
fi

Or in our case we wanted a one liner that generates an error if the process is NOT in a container

bash -c "test -h /proc/4129/ns/pid && test $(readlink /proc/4129/ns/pid) != $(readlink /proc/1/ns/pid)"

which we can execute from another process and if the exit code is zero then the specified PID is running in a different namespace.