90 lines
3.5 KiB
XML
90 lines
3.5 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-getting-sources">
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<title>Getting the Sources</title>
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<para>
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By default, NixOS’s <literal>nixos-rebuild</literal> command uses
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the NixOS and Nixpkgs sources provided by the
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<literal>nixos</literal> channel (kept in
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<literal>/nix/var/nix/profiles/per-user/root/channels/nixos</literal>).
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To modify NixOS, however, you should check out the latest sources
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from Git. This is as follows:
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</para>
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<programlisting>
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$ git clone https://github.com/NixOS/nixpkgs
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$ cd nixpkgs
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$ git remote update origin
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</programlisting>
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<para>
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This will check out the latest Nixpkgs sources to
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<literal>./nixpkgs</literal> the NixOS sources to
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<literal>./nixpkgs/nixos</literal>. (The NixOS source tree lives in
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a subdirectory of the Nixpkgs repository.) The
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<literal>nixpkgs</literal> repository has branches that correspond
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to each Nixpkgs/NixOS channel (see <xref linkend="sec-upgrading" />
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for more information about channels). Thus, the Git branch
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<literal>origin/nixos-17.03</literal> will contain the latest built
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and tested version available in the <literal>nixos-17.03</literal>
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channel.
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</para>
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<para>
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It’s often inconvenient to develop directly on the master branch,
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since if somebody has just committed (say) a change to GCC, then the
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binary cache may not have caught up yet and you’ll have to rebuild
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everything from source. So you may want to create a local branch
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based on your current NixOS version:
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</para>
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<programlisting>
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$ nixos-version
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17.09pre104379.6e0b727 (Hummingbird)
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$ git checkout -b local 6e0b727
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</programlisting>
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<para>
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Or, to base your local branch on the latest version available in a
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NixOS channel:
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</para>
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<programlisting>
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$ git remote update origin
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$ git checkout -b local origin/nixos-17.03
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</programlisting>
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<para>
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(Replace <literal>nixos-17.03</literal> with the name of the channel
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you want to use.) You can use <literal>git merge</literal> or
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<literal>git rebase</literal> to keep your local branch in sync with
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the channel, e.g.
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</para>
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<programlisting>
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$ git remote update origin
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$ git merge origin/nixos-17.03
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</programlisting>
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<para>
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You can use <literal>git cherry-pick</literal> to copy commits from
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your local branch to the upstream branch.
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</para>
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<para>
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If you want to rebuild your system using your (modified) sources,
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you need to tell <literal>nixos-rebuild</literal> about them using
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the <literal>-I</literal> flag:
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</para>
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<programlisting>
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# nixos-rebuild switch -I nixpkgs=/my/sources/nixpkgs
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</programlisting>
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<para>
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If you want <literal>nix-env</literal> to use the expressions in
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<literal>/my/sources</literal>, use
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<literal>nix-env -f /my/sources/nixpkgs</literal>, or change the
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default by adding a symlink in <literal>~/.nix-defexpr</literal>:
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</para>
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<programlisting>
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$ ln -s /my/sources/nixpkgs ~/.nix-defexpr/nixpkgs
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</programlisting>
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<para>
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You may want to delete the symlink
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<literal>~/.nix-defexpr/channels_root</literal> to prevent root’s
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NixOS channel from clashing with your own tree (this may break the
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command-not-found utility though). If you want to go back to the
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default state, you may just remove the
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<literal>~/.nix-defexpr</literal> directory completely, log out and
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log in again and it should have been recreated with a link to the
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root channels.
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</para>
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</chapter>
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