How We Run as a Non-Root Inside Docker Container

Docker starts a process inside its container as a “root” user. In some cases, this is not convenient though. For example, initdb from PostgreSQL doesn’t like to be started as root and will fail. In rultor.com, a DevOps team assistant, we’re using Docker as a virtualization technology for every build we run.

Here is how we change the user inside a running container, right after it is started.

First, this is how we start a new Docker container:

$ sudo docker run -i -t --rm -v "$(pwd):/main" \
  yegor256/rultor /main/entry.sh

There are two files in the current directory: entry.sh and script.sh. entry.sh is the file being executed by Docker on start, and it contains the following:

#!/bin/bash
adduser --disabled-password --gecos '' r
adduser r sudo
echo '%sudo ALL=(ALL) NOPASSWD:ALL' >> /etc/sudoers
su -m r -c /home/r/script.sh

script.sh will be executed as a user r inside the container. And this r user will have sudo permissions. This is exactly what all projects, managing their DevOps procedures with rultor.com, need.