91 lines
2.7 KiB
XML
91 lines
2.7 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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version="5.0"
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xml:id="sec-changing-config">
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<title>Changing the Configuration</title>
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<para>The file <filename>/etc/nixos/configuration.nix</filename>
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contains the current configuration of your machine. Whenever you’ve
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changed something to that file, you should do
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<screen>
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$ nixos-rebuild switch</screen>
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to build the new configuration, make it the default configuration for
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booting, and try to realise the configuration in the running system
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(e.g., by restarting system services).</para>
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<warning><para>These commands must be executed as root, so you should
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either run them from a root shell or by prefixing them with
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<literal>sudo -i</literal>.</para></warning>
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<para>You can also do
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<screen>
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$ nixos-rebuild test</screen>
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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.</para>
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<para>There is also
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<screen>
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$ nixos-rebuild boot</screen>
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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).</para>
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<para>You can make your configuration show up in a different submenu
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of the GRUB 2 boot screen by giving it a different <emphasis>profile
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name</emphasis>, e.g.
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<screen>
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$ nixos-rebuild switch -p test </screen>
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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 “NixOS -
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Profile 'test'”. This can be useful to separate test configurations
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from “stable” configurations.</para>
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<para>Finally, you can do
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<screen>
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$ nixos-rebuild build</screen>
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to build the configuration but nothing more. This is useful to see
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whether everything compiles cleanly.</para>
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<para>If you have a machine that supports hardware virtualisation, you
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can also test the new configuration in a sandbox by building and
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running a QEMU <emphasis>virtual machine</emphasis> that contains the
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desired configuration. Just do
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<screen>
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$ nixos-rebuild build-vm
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$ ./result/bin/run-*-vm
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</screen>
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The VM does not have any data from your host system, so your existing
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user accounts and home directories will not be available. You can
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forward ports on the host to the guest. For instance, the following
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will forward host port 2222 to guest port 22 (SSH):
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<screen>
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$ QEMU_NET_OPTS="hostfwd=tcp::2222-:22" ./result/bin/run-*-vm
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</screen>
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allowing you to log in via SSH (assuming you have set the appropriate
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passwords or SSH authorized keys):
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<screen>
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$ ssh -p 2222 localhost
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</screen>
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</para>
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</chapter>
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