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<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>
<prompt># </prompt>nixos-container create <replaceable>foo</replaceable>
</screen>
This creates the container’s root directory in
<filename>/var/lib/containers/<replaceable>foo</replaceable></filename> and a small configuration file
in <filename>/etc/containers/<replaceable>foo</replaceable>.conf</filename>. It also builds the
container’s initial system configuration and stores it in
<filename>/nix/var/nix/profiles/per-container/<replaceable>foo</replaceable>/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>
<prompt># </prompt>nixos-container create <replaceable>foo</replaceable> --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>
<prompt># </prompt>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>
<prompt># </prompt>nixos-container start <replaceable>foo</replaceable>
</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>
<prompt># </prompt>systemctl status container@<replaceable>foo</replaceable>
</screen>
</para>
<para>
If the container has started successfully, you can log in as root using the
<command>root-login</command> operation:
<screen>
<prompt># </prompt>nixos-container root-login <replaceable>foo</replaceable>
<prompt>[root@foo:~]#</prompt>
</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>
<prompt># </prompt>nixos-container login <replaceable>foo</replaceable>
foo login: alice
Password: ***
</screen>
With <command>nixos-container run</command>, you can execute arbitrary
commands in the container:
<screen>
<prompt># </prompt>nixos-container run <replaceable>foo</replaceable> -- 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>
<prompt># </prompt>nixos-container update <replaceable>foo</replaceable>
</screen>
This will build and activate the new configuration. You can also specify a
new configuration on the command line:
<screen>
<prompt># </prompt>nixos-container update <replaceable>foo</replaceable> --config '
<xref linkend="opt-services.httpd.enable"/> = true;
<xref linkend="opt-services.httpd.adminAddr"/> = "foo@example.org";
<xref linkend="opt-networking.firewall.allowedTCPPorts"/> = [ 80 ];
'
<prompt># </prompt>curl http://$(nixos-container show-ip <replaceable>foo</replaceable>)/
<!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>
<prompt># </prompt>nixos-container destroy <replaceable>foo</replaceable>
</screen>
</para>
</section>
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