[debian] 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

If you're running a CentOS container, you can install ps using this command:

yum install -y procps

Running this command on Dockerfile:

RUN yum install -y procps

In case you can't install the procps package (don't have proper permissions) you can use /proc directory.

The first few directories (named as numbers) are PIDs of your processes. Inside directories, you can find additional information useful to decipher which process is connected to each PID. For example, you can use the cat command to view "cmdline" file to check which process is connected to PID.

$ ls /proc
1 10 11 ...

$ ls -1 /proc/22
attr
autogroup
auxv
cgroup
clear_refs
cmdline
...

$ cat /proc/22/cmdline 
/bin/sh

use docker top

docker top <container ID>

Firstly, run the command below:

apt-get update && apt-get install procps

and then run:

ps -ef