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117 lines
3.9 KiB
117 lines
3.9 KiB
<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-changing-config">
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<title>Changing the Configuration</title>
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<para>
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The file <literal>/etc/nixos/configuration.nix</literal> contains
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the current configuration of your machine. Whenever you’ve
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<link linkend="ch-configuration">changed something</link> in that
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file, you should do
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</para>
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<programlisting>
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# nixos-rebuild switch
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</programlisting>
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<para>
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to build the new configuration, make it the default configuration
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for booting, and try to realise the configuration in the running
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system (e.g., by restarting system services).
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</para>
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<warning>
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<para>
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This command doesn't start/stop
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<link linkend="opt-systemd.user.services">user services</link>
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automatically. <literal>nixos-rebuild</literal> only runs a
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<literal>daemon-reload</literal> for each user with running user
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services.
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</para>
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</warning>
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<warning>
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<para>
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These commands must be executed as root, so you should either run
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them from a root shell or by prefixing them with
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<literal>sudo -i</literal>.
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</para>
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</warning>
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<para>
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You can also do
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</para>
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<programlisting>
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# nixos-rebuild test
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</programlisting>
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<para>
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to build the configuration and switch the running system to it, but
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without making it the boot default. So if (say) the configuration
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locks up your machine, you can just reboot to get back to a working
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configuration.
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</para>
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<para>
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There is also
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</para>
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<programlisting>
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# nixos-rebuild boot
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</programlisting>
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<para>
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to build the configuration and make it the boot default, but not
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switch to it now (so it will only take effect after the next
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reboot).
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</para>
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<para>
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You can make your configuration show up in a different submenu of
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the GRUB 2 boot screen by giving it a different <emphasis>profile
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name</emphasis>, e.g.
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</para>
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<programlisting>
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# nixos-rebuild switch -p test
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</programlisting>
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<para>
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which causes the new configuration (and previous ones created using
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<literal>-p test</literal>) to show up in the GRUB submenu
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<quote>NixOS - Profile 'test'</quote>. This can be useful to
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separate test configurations from <quote>stable</quote>
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configurations.
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</para>
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<para>
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Finally, you can do
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</para>
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<programlisting>
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$ nixos-rebuild build
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</programlisting>
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<para>
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to build the configuration but nothing more. This is useful to see
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whether everything compiles cleanly.
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</para>
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<para>
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If you have a machine that supports hardware virtualisation, you can
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also test the new configuration in a sandbox by building and running
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a QEMU <emphasis>virtual machine</emphasis> that contains the
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desired configuration. Just do
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</para>
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<programlisting>
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$ nixos-rebuild build-vm
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$ ./result/bin/run-*-vm
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</programlisting>
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<para>
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The VM does not have any data from your host system, so your
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existing user accounts and home directories will not be available
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unless you have set <literal>mutableUsers = false</literal>. Another
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way is to temporarily add the following to your configuration:
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</para>
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<programlisting language="bash">
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users.users.your-user.initialHashedPassword = "test";
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</programlisting>
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<para>
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<emphasis>Important:</emphasis> delete the $hostname.qcow2 file if
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you have started the virtual machine at least once without the right
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users, otherwise the changes will not get picked up. You can forward
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ports on the host to the guest. For instance, the following will
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forward host port 2222 to guest port 22 (SSH):
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</para>
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<programlisting>
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$ QEMU_NET_OPTS="hostfwd=tcp::2222-:22" ./result/bin/run-*-vm
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</programlisting>
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<para>
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allowing you to log in via SSH (assuming you have set the
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appropriate passwords or SSH authorized keys):
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</para>
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<programlisting>
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$ ssh -p 2222 localhost
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</programlisting>
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</chapter>
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