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OpenSSH server

Run a confined SSH server inside a Docker container - Made for ssh tunneling or backup apps which uses sftp (like Duplicati)

This container may not be for everybody as I have made a few decisions to suit my needs:

  • Requires key based authentication (map a directory containing .ssh/authorized keys to /config) or setting a password from the environment.
  • Either use the host's sshd keys or accept that new host keys will be generated when the container is regenerated (or generate a new, permanent, set of host keys and map them into the container)

Usage

docker run --name sshd -p 8022:22 -v /etc/ssh:/etc/ssh:ro -v ./ssh-home:/config ajoergensen/openssh-server

Environment

  • APP_PASSWORD: Set password for the app user. The variable is removed from inside the container once the password is set but it will be visible to anyone able to run docker inspect on the host
  • APP_PASSWORD_CRYPT: Set password for the app user. Encrypted string. This takes precedence over APP_PASSWORD
  • DISABLE_KEYGEN: To no attempt to generate ssh host keys. If the key(s) already exist they are never overwritten. Defaults to FALSE
  • DISABLE_CONFIG_GEN: Do not generate sshd_config. Set this if you mount an external sshd_config into the container. Defaults to FALSE
  • SSH_PORT: Port sshd is listening on. Useful if using --net host. Default is 22
  • SSH_PERMIT_ROOT_LOGIN: Sets PermitRootLogin, possible values are yes, no, forced-command-only, without-password, prohibit-password. Default is prohibit-password
  • SSH_AUTHORIZED_KEYS_DIR: Where sshd will look for the user's authorized_keys. Default is .ssh/authorized_keys
  • SSH_GATEWAY_PORTS: Specifies whether remote hosts are allowed to connect to ports forwarded for the client. Default is no

The rest of the available environment variables are described here

Volumes

The app user's $HOME is set to /config which is defined as a volume. ssh host keys can be placed in /etc/ssh/keys

Security

As mentioned, the APP_PASSWORD variable will expose the app users password to anyone with access to Docker on the host machine. It is recommended to use either APP_PASSWORD_CRYPT or key based authentication.