harshavardhanj/openssh repository overview

⁠Supported tags and respective Dockerfile links

• alpine, latest (OpenSSH/Dockerfile)⁠
• debian (OpenSSH/Dockerfile)⁠

⁠Quick reference

• Maintained by: Harsha Vardhan J⁠

• Source of this description: README in docker_files repository⁠

⁠Software Packages installed

• OpenSSH Server (latest version)

⁠Description of tags

⁠alpine, latest

The image with this tag contains the following software packages installed on top of the base Alpine Linux image.

• OpenSSH Server (latest version)

To use this image, use the alpine tag as follows

$ docker container run -d --name ssh -p "2222:22/tcp" \
harshavardhanj/openssh:alpine

or

$ docker container run -d --name ssh -p "2222:22/tcp" \
harshavardhanj/openssh:latest

or

$ docker container run -d --name ssh -p "2222:22/tcp" \
harshavardhanj/openssh

Any of the above commands will pull the image with the alpine tag.

⁠debian

The image with this tag contains the following software packages installed on top of the base Debian Stretch image.

• OpenSSH Server (latest version)

This image is considerably larger in size than the alpine or alpine-bash images as it is based on Debian. But, this image will come with a lot of tools and utilities installed by default.

$ docker container run -d --name ssh -p "2222:22/tcp" \
harshavardhanj/openssh:debian

⁠How to use this image

⁠Start an OpenSSH instance

$ docker container run -d --name ssh-server --publish "2222:22/tcp" \
-e USER='test_user' -e PASSWORD='test_password' harshavardhanj/openssh

This image includes EXPOSE 22 (the standard SSH port), so standard container linking will make it automatically available to linked containers. The default user that you can login as is created in the entrypoint script.

⁠... via docker stack deploy⁠ or docker-compose⁠

Example stack.yml for openssh:

# Use OpenSSH example user/password credentials
version: '3.4'

services:
	ssh:
    image: harshavardhanj/openssh:latest
    ports:
      - "2222:22"
    restart: always
    environment:
      - USER=example
      - PASSWORD=example

To use in a swarm, run docker stack deploy -c stack.yml harshavardhanj/openssh from the manager node in your swarm, wait for it to initialize completely, and try to connect using ssh example@swarm-ip -p 2222.

To use on a local development machine, use docker-compose -f stack.yml up from your local machine, wait for it to initialize completely, and try to connect using ssh example@localhost -p 2222, or ssh example@host-ip -p 2222 (as appropriate).

⁠Environment Variables

The OpenSSH image uses three environment variables. While none of the variables are required, they will aid you in customising certain aspects of the OpenSSH server for better security.

⁠USER

This environment variable is used in conjunction with PASSWORD to set its username and password. This variable will create the specified user that you can login as. If it is not specified, then the default user of docker will be used. If only the USER variable is specified, the default password will be assigned to the specified user. When a container is run by the command given below,

$ docker container run --name ssh -p "2222:22/tcp" \
-e USER='test_user' -d harshavardhanj/openssh

you can SSH into the container by logging in as the user test_user with the password docker.

⁠PASSWORD

This environment variable is recommended for you to use the OpenSSH image. This environment variable sets the password for user that is defined by the USER environment variable. The default user is defined by the USER environment variable. If the PASSWORD environment variable is not specified, the default value of docker is used. If only the PASSWORD variable is specified, the default user, docker, will be assigned the password specified. When a container is run by the command given below,

$ docker container run --name ssh -p "2222:22/tcp" \
-e PASSWORD='test_password' -d harshavardhanj/openssh

you can SSH into the container by logging in as the user docker with the password test_password.

⁠SSH_PUBKEY

This environment variable is recommended for you to use the OpenSSH image. This environment variable adds the SSH public-key for the user defined by the USER environment variable. Using the SSH_PUBKEY variable, you can login using key-based authentication. It is preferable to use docker secrets to pass the SSH_PUBKEY environment variable. If this not possible, you can pass the public-key as follows

$ docker container run --name ssh -p "2222:22/tcp" \
-e SSH_PUBKEY="$(cat /path/to/public/key.pub)" -d harshavardhanj/openssh

The double-quotes for passing the public-key is necessary to prevent word-splitting by the shell.

⁠Docker Secrets

As an alternative to passing sensitive information via environment variables, _FILE may be appended to the previously listed environment variables, causing the initialization script to load the values for those variables from files present in the container. In particular, this can be used to load passwords from Docker secrets stored in /run/secrets/<secret_name> files. For example:

$ docker container run --name ssh -p "2222:22/tcp" \
-e PASSWORD_FILE=/run/secrets/ssh_password -d harshavardhanj/openssh

⁠Image Variants

The openssh image comes in two flavours currently. One is based on Alpine Linux and the other on Debian Stretch

⁠openssh:alpine, openssh:latest, openssh

These images are based on the popular Alpine Linux project⁠, available in the alpine official image⁠. Alpine Linux is much smaller than most distribution base images (~5MB), and thus leads to much slimmer images in general.

This variant is highly recommended when final image size being as small as possible is desired. The main caveat to note is that it does use musl libc⁠ instead of glibc and friends⁠, so certain software might run into issues depending on the depth of their libc requirements. However, most software doesn't have an issue with this, so this variant is usually a very safe choice. See this Hacker News comment thread⁠ for more discussion of the issues that might arise and some pro/con comparisons of using Alpine-based images.

To minimize image size, it's uncommon for additional related tools (such as git or bash) to be included in Alpine-based images. Using this image as a base, add the things you need in your own Dockerfile (see the alpine image description⁠ for examples of how to install packages if you are unfamiliar).

⁠openssh:debian

This image is based on Debian Stretch Slim, available in the debian official image⁠. This image is considerably larger in size when compared to the images based on Alpine Linux, but it has the advantage of having a larger number of tools and utilities preinstalled in the base image.

⁠License

As with all Docker images, these likely also contain other software which may be under other licenses (such as bash, etc from the base distribution, along with any direct or indirect dependencies of the primary software being contained).

As for any pre-built image usage, it is the image user's responsibility to ensure that any use of this image complies with any relevant licenses for all software contained within.