<section  xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
          xmlns:xi="http://www.w3.org/2001/XInclude"
          version="5.0"
          xml:id="sec-imperative-containers">
 <title>Imperative Container Management</title>

 <para>
  We’ll cover imperative container management using
  <command>nixos-container</command> 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:
<screen>
# nixos-container create foo
</screen>
  This creates the container’s root directory in
  <filename>/var/lib/containers/foo</filename> and a small configuration file
  in <filename>/etc/containers/foo.conf</filename>. It also builds the
  container’s initial system configuration and stores it in
  <filename>/nix/var/nix/profiles/per-container/foo/system</filename>. You can
  modify the initial configuration of the container on the command line. For
  instance, to create a container that has <command>sshd</command> running,
  with the given public key for <literal>root</literal>:
<screen>
# nixos-container create foo --config '
  <xref linkend="opt-services.openssh.enable"/> = true;
  <link linkend="opt-users.users._name__.openssh.authorizedKeys.keys">users.users.root.openssh.authorizedKeys.keys</link> = ["ssh-dss AAAAB3N…"];
'
</screen>
  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>:
<screen>
# nixos-container create test --config-file test-container.nix \
    --local-address 10.235.1.2 --host-address 10.235.1.1
</screen>
 </para>

 <para>
  Creating a container does not start it. To start the container, run:
<screen>
# nixos-container start foo
</screen>
  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@<replaceable>container-name</replaceable>.service</literal>.
  Thus, if something went wrong, you can get status info using
  <command>systemctl</command>:
<screen>
# systemctl status container@foo
</screen>
 </para>

 <para>
  If the container has started successfully, you can log in as root using the
  <command>root-login</command> operation:
<screen>
# nixos-container root-login foo
[root@foo:~]#
</screen>
  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
  <command>login</command> operation, which is available to all users on the
  host:
<screen>
# nixos-container login foo
foo login: alice
Password: ***
</screen>
  With <command>nixos-container run</command>, you can execute arbitrary
  commands in the container:
<screen>
# 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
</screen>
 </para>

 <para>
  There are several ways to change the configuration of the container. First,
  on the host, you can edit
  <literal>/var/lib/container/<replaceable>name</replaceable>/etc/nixos/configuration.nix</literal>,
  and run
<screen>
# nixos-container update foo
</screen>
  This will build and activate the new configuration. You can also specify a
  new configuration on the command line:
<screen>
# nixos-container update foo --config '
  <xref linkend="opt-services.httpd.enable"/> = true;
  <xref linkend="opt-services.httpd.adminAddr"/> = "foo@example.org";
  <xref linkend="opt-networking.firewall.allowedTCPPorts"/> = [ 80 ];
'

# curl http://$(nixos-container show-ip foo)/
&lt;!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">…
</screen>
  However, note that this will overwrite the container’s
  <filename>/etc/nixos/configuration.nix</filename>.
 </para>

 <para>
  Alternatively, you can change the configuration from within the container
  itself by running <command>nixos-rebuild switch</command> inside the
  container. Note that the container by default does not have a copy of the
  NixOS channel, so you should run <command>nix-channel --update</command>
  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 <command>systemctl</command> on the container’s service unit. To
  destroy a container, including its file system, do
<screen>
# nixos-container destroy foo
</screen>
 </para>
</section>
