ssh-keyscan not found in Dockerfile

Question

I have a simple Dockerfile, exactly as below:

FROM ubuntu:14.04  RUN apt-get update RUN apt-get -y upgrade  RUN mkdir -p /root/.ssh RUN touch /root/.ssh/known_hosts  RUN ssh-keyscan github.com >> /root/.ssh/known_hosts 

The result of running:

docker build -no-cache -t testimage . 

is:

Step 5 : RUN ssh-keyscan github.com >> /root/.ssh/known_hosts  ---> Running in e11ef5962a11 /bin/sh: 1: ssh-keyscan: not found 

Answer 1

You would need to install ssh first.

RUN  apt-get -yq update && \      apt-get -yqq install ssh 

Then, the various ssh commands, including ssh-keyscan, would be available.

That is what I did in my sshd image Dockerfile.
I used it to add localhost to my .ssh/known_hosts in order to make some test locally on the sshd server.

As commented below by pjotr-dolphin:

If you are only after ssh-keyscan, openssh-client has smaller footprint than ssh package.

Actually, package openssh-clients for RedHat/CentOS, as commented by Oleg Neumyvakin