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1<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-installing-from-other-distro">
2 <title>Installing from another Linux distribution</title>
3 <para>
4 Because Nix (the package manager) & Nixpkgs (the Nix packages
5 collection) can both be installed on any (most?) Linux
6 distributions, they can be used to install NixOS in various creative
7 ways. You can, for instance:
8 </para>
9 <orderedlist numeration="arabic">
10 <listitem>
11 <para>
12 Install NixOS on another partition, from your existing Linux
13 distribution (without the use of a USB or optical device!)
14 </para>
15 </listitem>
16 <listitem>
17 <para>
18 Install NixOS on the same partition (in place!), from your
19 existing non-NixOS Linux distribution using
20 <literal>NIXOS_LUSTRATE</literal>.
21 </para>
22 </listitem>
23 <listitem>
24 <para>
25 Install NixOS on your hard drive from the Live CD of any Linux
26 distribution.
27 </para>
28 </listitem>
29 </orderedlist>
30 <para>
31 The first steps to all these are the same:
32 </para>
33 <orderedlist numeration="arabic">
34 <listitem>
35 <para>
36 Install the Nix package manager:
37 </para>
38 <para>
39 Short version:
40 </para>
41 <programlisting>
42$ curl -L https://nixos.org/nix/install | sh
43$ . $HOME/.nix-profile/etc/profile.d/nix.sh # …or open a fresh shell
44</programlisting>
45 <para>
46 More details in the
47 <link xlink:href="https://nixos.org/nix/manual/#chap-quick-start">
48 Nix manual</link>
49 </para>
50 </listitem>
51 <listitem>
52 <para>
53 Switch to the NixOS channel:
54 </para>
55 <para>
56 If you've just installed Nix on a non-NixOS distribution, you
57 will be on the <literal>nixpkgs</literal> channel by default.
58 </para>
59 <programlisting>
60$ nix-channel --list
61nixpkgs https://nixos.org/channels/nixpkgs-unstable
62</programlisting>
63 <para>
64 As that channel gets released without running the NixOS tests,
65 it will be safer to use the <literal>nixos-*</literal> channels
66 instead:
67 </para>
68 <programlisting>
69$ nix-channel --add https://nixos.org/channels/nixos-version nixpkgs
70</programlisting>
71 <para>
72 You may want to throw in a
73 <literal>nix-channel --update</literal> for good measure.
74 </para>
75 </listitem>
76 <listitem>
77 <para>
78 Install the NixOS installation tools:
79 </para>
80 <para>
81 You'll need <literal>nixos-generate-config</literal> and
82 <literal>nixos-install</literal>, but this also makes some man
83 pages and <literal>nixos-enter</literal> available, just in case
84 you want to chroot into your NixOS partition. NixOS installs
85 these by default, but you don't have NixOS yet..
86 </para>
87 <programlisting>
88$ nix-env -f '<nixpkgs>' -iA nixos-install-tools
89</programlisting>
90 </listitem>
91 <listitem>
92 <note>
93 <para>
94 The following 5 steps are only for installing NixOS to another
95 partition. For installing NixOS in place using
96 <literal>NIXOS_LUSTRATE</literal>, skip ahead.
97 </para>
98 </note>
99 <para>
100 Prepare your target partition:
101 </para>
102 <para>
103 At this point it is time to prepare your target partition.
104 Please refer to the partitioning, file-system creation, and
105 mounting steps of <xref linkend="sec-installation" />
106 </para>
107 <para>
108 If you're about to install NixOS in place using
109 <literal>NIXOS_LUSTRATE</literal> there is nothing to do for
110 this step.
111 </para>
112 </listitem>
113 <listitem>
114 <para>
115 Generate your NixOS configuration:
116 </para>
117 <programlisting>
118$ sudo `which nixos-generate-config` --root /mnt
119</programlisting>
120 <para>
121 You'll probably want to edit the configuration files. Refer to
122 the <literal>nixos-generate-config</literal> step in
123 <xref linkend="sec-installation" /> for more information.
124 </para>
125 <para>
126 Consider setting up the NixOS bootloader to give you the ability
127 to boot on your existing Linux partition. For instance, if
128 you're using GRUB and your existing distribution is running
129 Ubuntu, you may want to add something like this to your
130 <literal>configuration.nix</literal>:
131 </para>
132 <programlisting language="bash">
133boot.loader.grub.extraEntries = ''
134 menuentry "Ubuntu" {
135 search --set=ubuntu --fs-uuid 3cc3e652-0c1f-4800-8451-033754f68e6e
136 configfile "($ubuntu)/boot/grub/grub.cfg"
137 }
138'';
139</programlisting>
140 <para>
141 (You can find the appropriate UUID for your partition in
142 <literal>/dev/disk/by-uuid</literal>)
143 </para>
144 </listitem>
145 <listitem>
146 <para>
147 Create the <literal>nixbld</literal> group and user on your
148 original distribution:
149 </para>
150 <programlisting>
151$ sudo groupadd -g 30000 nixbld
152$ sudo useradd -u 30000 -g nixbld -G nixbld nixbld
153</programlisting>
154 </listitem>
155 <listitem>
156 <para>
157 Download/build/install NixOS:
158 </para>
159 <warning>
160 <para>
161 Once you complete this step, you might no longer be able to
162 boot on existing systems without the help of a rescue USB
163 drive or similar.
164 </para>
165 </warning>
166 <note>
167 <para>
168 On some distributions there are separate PATHS for programs
169 intended only for root. In order for the installation to
170 succeed, you might have to use
171 <literal>PATH="$PATH:/usr/sbin:/sbin"</literal> in
172 the following command.
173 </para>
174 </note>
175 <programlisting>
176$ sudo PATH="$PATH" NIX_PATH="$NIX_PATH" `which nixos-install` --root /mnt
177</programlisting>
178 <para>
179 Again, please refer to the <literal>nixos-install</literal> step
180 in <xref linkend="sec-installation" /> for more information.
181 </para>
182 <para>
183 That should be it for installation to another partition!
184 </para>
185 </listitem>
186 <listitem>
187 <para>
188 Optionally, you may want to clean up your non-NixOS
189 distribution:
190 </para>
191 <programlisting>
192$ sudo userdel nixbld
193$ sudo groupdel nixbld
194</programlisting>
195 <para>
196 If you do not wish to keep the Nix package manager installed
197 either, run something like
198 <literal>sudo rm -rv ~/.nix-* /nix</literal> and remove the line
199 that the Nix installer added to your
200 <literal>~/.profile</literal>.
201 </para>
202 </listitem>
203 <listitem>
204 <note>
205 <para>
206 The following steps are only for installing NixOS in place
207 using <literal>NIXOS_LUSTRATE</literal>:
208 </para>
209 </note>
210 <para>
211 Generate your NixOS configuration:
212 </para>
213 <programlisting>
214$ sudo `which nixos-generate-config` --root /
215</programlisting>
216 <para>
217 Note that this will place the generated configuration files in
218 <literal>/etc/nixos</literal>. You'll probably want to edit the
219 configuration files. Refer to the
220 <literal>nixos-generate-config</literal> step in
221 <xref linkend="sec-installation" /> for more information.
222 </para>
223 <para>
224 You'll likely want to set a root password for your first boot
225 using the configuration files because you won't have a chance to
226 enter a password until after you reboot. You can initalize the
227 root password to an empty one with this line: (and of course
228 don't forget to set one once you've rebooted or to lock the
229 account with <literal>sudo passwd -l root</literal> if you use
230 <literal>sudo</literal>)
231 </para>
232 <programlisting language="bash">
233users.users.root.initialHashedPassword = "";
234</programlisting>
235 </listitem>
236 <listitem>
237 <para>
238 Build the NixOS closure and install it in the
239 <literal>system</literal> profile:
240 </para>
241 <programlisting>
242$ nix-env -p /nix/var/nix/profiles/system -f '<nixpkgs/nixos>' -I nixos-config=/etc/nixos/configuration.nix -iA system
243</programlisting>
244 </listitem>
245 <listitem>
246 <para>
247 Change ownership of the <literal>/nix</literal> tree to root
248 (since your Nix install was probably single user):
249 </para>
250 <programlisting>
251$ sudo chown -R 0:0 /nix
252</programlisting>
253 </listitem>
254 <listitem>
255 <para>
256 Set up the <literal>/etc/NIXOS</literal> and
257 <literal>/etc/NIXOS_LUSTRATE</literal> files:
258 </para>
259 <para>
260 <literal>/etc/NIXOS</literal> officializes that this is now a
261 NixOS partition (the bootup scripts require its presence).
262 </para>
263 <para>
264 <literal>/etc/NIXOS_LUSTRATE</literal> tells the NixOS bootup
265 scripts to move <emphasis>everything</emphasis> that's in the
266 root partition to <literal>/old-root</literal>. This will move
267 your existing distribution out of the way in the very early
268 stages of the NixOS bootup. There are exceptions (we do need to
269 keep NixOS there after all), so the NixOS lustrate process will
270 not touch:
271 </para>
272 <itemizedlist>
273 <listitem>
274 <para>
275 The <literal>/nix</literal> directory
276 </para>
277 </listitem>
278 <listitem>
279 <para>
280 The <literal>/boot</literal> directory
281 </para>
282 </listitem>
283 <listitem>
284 <para>
285 Any file or directory listed in
286 <literal>/etc/NIXOS_LUSTRATE</literal> (one per line)
287 </para>
288 </listitem>
289 </itemizedlist>
290 <note>
291 <para>
292 Support for <literal>NIXOS_LUSTRATE</literal> was added in
293 NixOS 16.09. The act of "lustrating" refers to the
294 wiping of the existing distribution. Creating
295 <literal>/etc/NIXOS_LUSTRATE</literal> can also be used on
296 NixOS to remove all mutable files from your root partition
297 (anything that's not in <literal>/nix</literal> or
298 <literal>/boot</literal> gets "lustrated" on the
299 next boot.
300 </para>
301 <para>
302 lustrate /ˈlʌstreɪt/ verb.
303 </para>
304 <para>
305 purify by expiatory sacrifice, ceremonial washing, or some
306 other ritual action.
307 </para>
308 </note>
309 <para>
310 Let's create the files:
311 </para>
312 <programlisting>
313$ sudo touch /etc/NIXOS
314$ sudo touch /etc/NIXOS_LUSTRATE
315</programlisting>
316 <para>
317 Let's also make sure the NixOS configuration files are kept once
318 we reboot on NixOS:
319 </para>
320 <programlisting>
321$ echo etc/nixos | sudo tee -a /etc/NIXOS_LUSTRATE
322</programlisting>
323 </listitem>
324 <listitem>
325 <para>
326 Finally, move the <literal>/boot</literal> directory of your
327 current distribution out of the way (the lustrate process will
328 take care of the rest once you reboot, but this one must be
329 moved out now because NixOS needs to install its own boot files:
330 </para>
331 <warning>
332 <para>
333 Once you complete this step, your current distribution will no
334 longer be bootable! If you didn't get all the NixOS
335 configuration right, especially those settings pertaining to
336 boot loading and root partition, NixOS may not be bootable
337 either. Have a USB rescue device ready in case this happens.
338 </para>
339 </warning>
340 <programlisting>
341$ sudo mv -v /boot /boot.bak &&
342sudo /nix/var/nix/profiles/system/bin/switch-to-configuration boot
343</programlisting>
344 <para>
345 Cross your fingers, reboot, hopefully you should get a NixOS
346 prompt!
347 </para>
348 </listitem>
349 <listitem>
350 <para>
351 If for some reason you want to revert to the old distribution,
352 you'll need to boot on a USB rescue disk and do something along
353 these lines:
354 </para>
355 <programlisting>
356# mkdir root
357# mount /dev/sdaX root
358# mkdir root/nixos-root
359# mv -v root/* root/nixos-root/
360# mv -v root/nixos-root/old-root/* root/
361# mv -v root/boot.bak root/boot # We had renamed this by hand earlier
362# umount root
363# reboot
364</programlisting>
365 <para>
366 This may work as is or you might also need to reinstall the boot
367 loader.
368 </para>
369 <para>
370 And of course, if you're happy with NixOS and no longer need the
371 old distribution:
372 </para>
373 <programlisting>
374sudo rm -rf /old-root
375</programlisting>
376 </listitem>
377 <listitem>
378 <para>
379 It's also worth noting that this whole process can be automated.
380 This is especially useful for Cloud VMs, where provider do not
381 provide NixOS. For instance,
382 <link xlink:href="https://github.com/elitak/nixos-infect">nixos-infect</link>
383 uses the lustrate process to convert Digital Ocean droplets to
384 NixOS from other distributions automatically.
385 </para>
386 </listitem>
387 </orderedlist>
388</section>