How to use sudo inside a docker container?

Normally, docker containers are run using the user root. I'd like to use a different user, which is no problem using docker's USER directive. But this user should be able to use sudo inside the container. This command is missing.

Here's a simple Dockerfile for this purpose:

FROM ubuntu:12.04

RUN useradd docker && echo "docker:docker" | chpasswd
RUN mkdir -p /home/docker && chown -R docker:docker /home/docker
   
USER docker
CMD /bin/bash

Running this container, I get logged in with user 'docker'. When I try to use sudo, the command isn't found. So I tried to install the sudo package inside my Dockerfile using

RUN apt-get install sudo

This results in Unable to locate package sudo

Just got it. As regan pointed out, I had to add the user to the sudoers group. But the main reason was I'd forgotten to update the repositories cache, so apt-get couldn't find the sudo package. It's working now. Here's the completed code:

FROM ubuntu:12.04

RUN apt-get update && \
      apt-get -y install sudo

RUN useradd -m docker && echo "docker:docker" | chpasswd && adduser docker sudo

USER docker
CMD /bin/bash

When neither sudo nor apt-get is available in container, you can also jump into running container as root user using command

docker exec -u root -t -i container_id /bin/bash

The other answers didn't work for me. I kept searching and found a blog post that covered how a team was running non-root inside of a docker container.

Here's the TL;DR version:

RUN apt-get update \
 && apt-get install -y sudo

RUN adduser --disabled-password --gecos '' docker
RUN adduser docker sudo
RUN echo '%sudo ALL=(ALL) NOPASSWD:ALL' >> /etc/sudoers

USER docker

# this is where I was running into problems with the other approaches
RUN sudo apt-get update 

I was using FROM node:9.3 for this, but I suspect that other similar container bases would work as well.

For anyone who has this issue with an already running container, and they don't necessarily want to rebuild, the following command connects to a running container with root privileges:

docker exec -ti -u root container_name bash

You can also connect using its ID, rather than its name, by finding it with:

docker ps -l

To save your changes so that they are still there when you next launch the container (or docker-compose cluster) - note that these changes would not be repeated if you rebuild from scratch:

docker commit container_id image_name

To roll back to a previous image version (warning: this deletes history rather than appends to the end, so to keep a reference to the current image, tag it first using the optional step):

docker history image_name
docker tag latest_image_id my_descriptive_tag_name  # optional
docker tag desired_history_image_id image_name

To start a container that isn't running and connect as root:

docker run -ti -u root --entrypoint=/bin/bash image_id_or_name -s

To copy from a running container:

docker cp <containerId>:/file/path/within/container /host/path/target

To export a copy of the image:

docker save container | gzip > /dir/file.tar.gz

Which you can restore to another Docker install using:

gzcat /dir/file.tar.gz | docker load

It is much quicker but takes more space to not compress, using:

docker save container | dir/file.tar

And:

cat dir/file.tar | docker load

if you want to connect to container and install something
using apt-get
first as above answer from our brother "Tomáš Záluský"

docker exec -u root -t -i container_id /bin/bash

then try to

> RUN apt-get update or apt-get 'anything you want'

it worked with me hope it's useful for all

Here's how I setup a non-root user with the base image of ubuntu:18.04:

RUN \
    groupadd -g 999 foo && useradd -u 999 -g foo -G sudo -m -s /bin/bash foo && \
    sed -i /etc/sudoers -re 's/^%sudo.*/%sudo ALL=(ALL:ALL) NOPASSWD: ALL/g' && \
    sed -i /etc/sudoers -re 's/^root.*/root ALL=(ALL:ALL) NOPASSWD: ALL/g' && \
    sed -i /etc/sudoers -re 's/^#includedir.*/## **Removed the include directive** ##"/g' && \
    echo "foo ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers && \
    echo "Customized the sudoers file for passwordless access to the foo user!" && \
    echo "foo user:";  su - foo -c id

What happens with the above code:

• The user and group foo is created.
• The user foo is added to the both the foo and sudo group.
• The uid and gid is set to the value of 999.
• The home directory is set to /home/foo.
• The shell is set to /bin/bash.
• The sed command does inline updates to the /etc/sudoers file to allow foo and root users passwordless access to the sudo group.
• The sed command disables the #includedir directive that would allow any files in subdirectories to override these inline updates.

If SUDO or apt-get is not accessible inside the Container, You can use, below option in running container.

docker exec -u root -it f83b5c5bf413 ash

"f83b5c5bf413" is my container ID & here is working example from my terminal:

Unlike accepted answer, I use usermod instead.

Assume already logged-in as root in docker, and "fruit" is the new non-root username I want to add, simply run this commands:

apt update && apt install sudo
adduser fruit
usermod -aG sudo fruit

Remember to save image after update. Use docker ps to get current running docker's <CONTAINER ID> and <IMAGE>, then run docker commit -m "added sudo user" <CONTAINER ID> <IMAGE> to save docker image.

Then test with:

su fruit
sudo whoami

Or test by direct login(ensure save image first) as that non-root user when launch docker:

docker run -it --user fruit <IMAGE>
sudo whoami

You can use sudo -k to reset password prompt timestamp:

sudo whoami # No password prompt
sudo -k # Invalidates the user's cached credentials
sudo whoami # This will prompt for password

This may not work for all images, but some images contain a root user already, such as in the jupyterhub/singleuser image. With that image it's simply:

USER root
RUN sudo apt-get update

If you have a container running as root that runs a script (which you can't change) that needs access to the sudo command, you can simply create a new sudo script in your $PATH that calls the passed command.

e.g. In your Dockerfile:

RUN if type sudo 2>/dev/null; then \ 
     echo "The sudo command already exists... Skipping."; \
    else \
     echo -e "#!/bin/sh\n\${@}" > /usr/sbin/sudo; \
     chmod +x /usr/sbin/sudo; \
    fi

There is no answer on how to do this on CentOS. On Centos, you can add following to Dockerfile

RUN echo "user ALL=(root) NOPASSWD:ALL" > /etc/sudoers.d/user && \
    chmod 0440 /etc/sudoers.d/user

An example Dockerfile for Centos7. In this example we add prod_user with privilege of sudo.

FROM centos:7

RUN yum -y update && yum clean all

RUN yum -y install openssh-server  python3 sudo

RUN adduser -m prod_user && \
    echo "MyPass*49?" | passwd prod_user --stdin && \
    usermod -aG wheel prod_user && \
    mkdir /home/prod_user/.ssh && \
    chown prod_user:prod_user -R  /home/prod_user/ && \
    chmod 700 /home/prod_user/.ssh

RUN echo "prod_user ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers && \
    echo "%wheel ALL=(ALL) ALL" >> /etc/sudoers

RUN echo "PasswordAuthentication yes" >> /etc/ssh/sshd_config

RUN systemctl enable sshd.service

VOLUME [ "/sys/fs/cgroup" ]

ENTRYPOINT ["/usr/sbin/init"]