Imperative Container Management

We'll cover imperative container management using nixos-container first. Be aware that container management is currently only possible as root.

You create a container with identifier foo as follows:

# nixos-container create foo

This creates the container's root directory in /var/lib/nixos-containers/foo and a small configuration file in /etc/nixos-containers/foo.conf. It also builds the container's initial system configuration and stores it in /nix/var/nix/profiles/per-container/foo/system. You can modify the initial configuration of the container on the command line. For instance, to create a container that has sshd running, with the given public key for root:

# nixos-container create foo --config '
  services.openssh.enable = true;
  users.users.root.openssh.authorizedKeys.keys = ["ssh-dss AAAAB3N…"];
'

By default the next free address in the 10.233.0.0/16 subnet will be chosen as container IP. This behavior can be altered by setting --host-address and --local-address:

# nixos-container create test --config-file test-container.nix \
    --local-address 10.235.1.2 --host-address 10.235.1.1

Creating a container does not start it. To start the container, run:

# nixos-container start foo

This command will return as soon as the container has booted and has reached multi-user.target. On the host, the container runs within a systemd unit called container@container-name.service. Thus, if something went wrong, you can get status info using systemctl:

# systemctl status container@foo

If the container has started successfully, you can log in as root using the root-login operation:

# nixos-container root-login foo
[root@foo:~]#

Note that only root on the host can do this (since there is no authentication). You can also get a regular login prompt using the login operation, which is available to all users on the host:

# nixos-container login foo
foo login: alice
Password: ***

With nixos-container run, you can execute arbitrary commands in the container:

# nixos-container run foo -- uname -a
Linux foo 3.4.82 #1-NixOS SMP Thu Mar 20 14:44:05 UTC 2014 x86_64 GNU/Linux

There are several ways to change the configuration of the container. First, on the host, you can edit /var/lib/container/name/etc/nixos/configuration.nix, and run

# nixos-container update foo

This will build and activate the new configuration. You can also specify a new configuration on the command line:

# nixos-container update foo --config '
  services.httpd.enable = true;
  services.httpd.adminAddr = "foo@example.org";
  networking.firewall.allowedTCPPorts = [ 80 ];
'

# curl http://$(nixos-container show-ip foo)/
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">…

However, note that this will overwrite the container's /etc/nixos/configuration.nix.

Alternatively, you can change the configuration from within the container itself by running nixos-rebuild switch inside the container. Note that the container by default does not have a copy of the NixOS channel, so you should run nix-channel --update first.

Containers can be stopped and started using nixos-container stop and nixos-container start, respectively, or by using systemctl on the container's service unit. To destroy a container, including its file system, do

# nixos-container destroy foo

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Imperative Container Management

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