ps command doesn't work in docker container

I want to do a ps command in a docker container derived from Debian official Docker hub repository:

$ docker run -ti debian:wheezy /bin/bash
root@51afd6b09af8:/# ps
bash: ps: command not found

alternative 1:

use docker top

docker top <container ID>

alternative 2 (but your container will be bloated):

ps is not installed in the base wheezy image. Try this from within the container:

apt-get update && apt-get install procps

or add the following line to the Dockerfile:

RUN apt-get update && apt-get install -y procps && rm -rf /var/lib/apt/lists/*