98 lines
3.7 KiB
XML
98 lines
3.7 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>
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The file <filename>/etc/nixos/configuration.nix</filename> contains the
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current configuration of your machine. Whenever you’ve
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<link linkend="ch-configuration">changed something</link> in that file, you
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should do
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<screen>
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<prompt># </prompt>nixos-rebuild switch
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</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 (e.g., by
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restarting system services).
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<warning>
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<para>
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This command doesn't start/stop <link linkend="opt-systemd.user.services">user
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services</link> automatically. <command>nixos-rebuild</command> only runs a
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<literal>daemon-reload</literal> for each user with running user services.
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</para>
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</warning>
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</para>
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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 them from
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a root shell or by prefixing them with <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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<screen>
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<prompt># </prompt>nixos-rebuild test
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</screen>
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to build the configuration and switch the running system to it, but without
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making it the boot default. So if (say) the configuration locks up your
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machine, you can just reboot to get back to a working configuration.
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</para>
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<para>
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There is also
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<screen>
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<prompt># </prompt>nixos-rebuild boot
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</screen>
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to build the configuration and make it the boot default, but not switch to it
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now (so it will only take effect after the next 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 the GRUB 2
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boot screen by giving it a different <emphasis>profile name</emphasis>, e.g.
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<screen>
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<prompt># </prompt>nixos-rebuild switch -p test
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</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 - Profile
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'test'”. This can be useful to separate test configurations from
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“stable” configurations.
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</para>
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<para>
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Finally, you can do
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<screen>
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<prompt>$ </prompt>nixos-rebuild build
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</screen>
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to build the configuration but nothing more. This is useful to see whether
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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 also
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test the new configuration in a sandbox by building and running a QEMU
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<emphasis>virtual machine</emphasis> that contains the desired configuration.
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Just do
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<screen>
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<prompt>$ </prompt>nixos-rebuild build-vm
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<prompt>$ </prompt>./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 user
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accounts and home directories will not be available unless you have set
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<literal>mutableUsers = false</literal>. Another way is to temporarily add
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the following to your configuration:
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<screen>
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<link linkend="opt-users.users._name_.initialHashedPassword">users.users.your-user.initialHashedPassword</link> = "test";
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</screen>
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<emphasis>Important:</emphasis> delete the $hostname.qcow2 file if you have
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started the virtual machine at least once without the right users, otherwise
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the changes will not get picked up. You can forward ports on the host to the
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guest. For instance, the following will forward host port 2222 to guest port
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22 (SSH):
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<screen>
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<prompt>$ </prompt>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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<prompt>$ </prompt>ssh -p 2222 localhost
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</screen>
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</para>
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</chapter>
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