<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-imperative-containers">
  <title>Imperative Container Management</title>
  <para>
    We’ll cover imperative container management using
    <literal>nixos-container</literal> first. Be aware that container
    management is currently only possible as <literal>root</literal>.
  </para>
  <para>
    You create a container with identifier <literal>foo</literal> as
    follows:
  </para>
  <programlisting>
# nixos-container create foo
</programlisting>
  <para>
    This creates the container’s root directory in
    <literal>/var/lib/containers/foo</literal> and a small configuration
    file in <literal>/etc/containers/foo.conf</literal>. It also builds
    the container’s initial system configuration and stores it in
    <literal>/nix/var/nix/profiles/per-container/foo/system</literal>.
    You can modify the initial configuration of the container on the
    command line. For instance, to create a container that has
    <literal>sshd</literal> running, with the given public key for
    <literal>root</literal>:
  </para>
  <programlisting>
# nixos-container create foo --config '
  services.openssh.enable = true;
  users.users.root.openssh.authorizedKeys.keys = [&quot;ssh-dss AAAAB3N…&quot;];
'
</programlisting>
  <para>
    By default the next free address in the
    <literal>10.233.0.0/16</literal> subnet will be chosen as container
    IP. This behavior can be altered by setting
    <literal>--host-address</literal> and
    <literal>--local-address</literal>:
  </para>
  <programlisting>
# nixos-container create test --config-file test-container.nix \
    --local-address 10.235.1.2 --host-address 10.235.1.1
</programlisting>
  <para>
    Creating a container does not start it. To start the container, run:
  </para>
  <programlisting>
# nixos-container start foo
</programlisting>
  <para>
    This command will return as soon as the container has booted and has
    reached <literal>multi-user.target</literal>. On the host, the
    container runs within a systemd unit called
    <literal>container@container-name.service</literal>. Thus, if
    something went wrong, you can get status info using
    <literal>systemctl</literal>:
  </para>
  <programlisting>
# systemctl status container@foo
</programlisting>
  <para>
    If the container has started successfully, you can log in as root
    using the <literal>root-login</literal> operation:
  </para>
  <programlisting>
# nixos-container root-login foo
[root@foo:~]#
</programlisting>
  <para>
    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
    <literal>login</literal> operation, which is available to all users
    on the host:
  </para>
  <programlisting>
# nixos-container login foo
foo login: alice
Password: ***
</programlisting>
  <para>
    With <literal>nixos-container run</literal>, you can execute
    arbitrary commands in the container:
  </para>
  <programlisting>
# 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
</programlisting>
  <para>
    There are several ways to change the configuration of the container.
    First, on the host, you can edit
    <literal>/var/lib/container/name/etc/nixos/configuration.nix</literal>,
    and run
  </para>
  <programlisting>
# nixos-container update foo
</programlisting>
  <para>
    This will build and activate the new configuration. You can also
    specify a new configuration on the command line:
  </para>
  <programlisting>
# nixos-container update foo --config '
  services.httpd.enable = true;
  services.httpd.adminAddr = &quot;foo@example.org&quot;;
  networking.firewall.allowedTCPPorts = [ 80 ];
'

# curl http://$(nixos-container show-ip foo)/
&lt;!DOCTYPE HTML PUBLIC &quot;-//W3C//DTD HTML 3.2 Final//EN&quot;&gt;…
</programlisting>
  <para>
    However, note that this will overwrite the container’s
    <literal>/etc/nixos/configuration.nix</literal>.
  </para>
  <para>
    Alternatively, you can change the configuration from within the
    container itself by running <literal>nixos-rebuild switch</literal>
    inside the container. Note that the container by default does not
    have a copy of the NixOS channel, so you should run
    <literal>nix-channel --update</literal> first.
  </para>
  <para>
    Containers can be stopped and started using
    <literal>nixos-container stop</literal> and
    <literal>nixos-container start</literal>, respectively, or by using
    <literal>systemctl</literal> on the container’s service unit. To
    destroy a container, including its file system, do
  </para>
  <programlisting>
# nixos-container destroy foo
</programlisting>
</section>
