How to know if a docker container is running in privileged mode

From the docker host

Use the docker inspect command:

docker inspect --format="{{.HostConfig.Privileged}}" <container id>

And within a bash script you could have a test:

if [[ $(docker inspect --format="{{.HostConfig.Privileged}}" <container id>) == "false" ]]; then
    echo not privileged
else
    echo privileged
fi

From inside the container itself

You have to try to run a command that requires the --privileged flag and see if it fails

For instance ip link add dummy0 type dummy is a command which requires the --privileged flag to be successful:

$ docker run --rm -it ubuntu ip link add dummy0 type dummy
RTNETLINK answers: Operation not permitted

while

$ docker run --rm -it --privileged ubuntu ip link add dummy0 type dummy

runs fine.

In a bash script you could do something similar to this:

ip link add dummy0 type dummy >/dev/null
if [[ $? -eq 0 ]]; then
    PRIVILEGED=true
    # clean the dummy0 link
    ip link delete dummy0 >/dev/null
else
    PRIVILEGED=false
fi