86 lines
3.9 KiB
XML
86 lines
3.9 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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xmlns:xi="http://www.w3.org/2001/XInclude"
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version="5.0"
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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 <command>nixos-rebuild</command> command uses the NixOS
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and Nixpkgs sources provided by the <literal>nixos</literal> channel (kept in
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<filename>/nix/var/nix/profiles/per-user/root/channels/nixos</filename>). To
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modify NixOS, however, you should check out the latest sources from Git. This
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is as follows:
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<screen>
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<prompt>$ </prompt>git clone https://github.com/NixOS/nixpkgs
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<prompt>$ </prompt>cd nixpkgs
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<prompt>$ </prompt>git remote add channels https://github.com/NixOS/nixpkgs-channels
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<prompt>$ </prompt>git remote update channels
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</screen>
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This will check out the latest Nixpkgs sources to
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<filename>./nixpkgs</filename> the NixOS sources to
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<filename>./nixpkgs/nixos</filename>. (The NixOS source tree lives in a
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subdirectory of the Nixpkgs repository.) The remote
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<literal>channels</literal> refers to a read-only repository that tracks the
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Nixpkgs/NixOS channels (see <xref linkend="sec-upgrading"/> for more
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information about channels). Thus, the Git branch
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<literal>channels/nixos-17.03</literal> will contain the latest built and
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tested version available in the <literal>nixos-17.03</literal> 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, since if
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somebody has just committed (say) a change to GCC, then the binary cache may
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not have caught up yet and you’ll have to rebuild everything from source.
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So you may want to create a local branch based on your current NixOS version:
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<screen>
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<prompt>$ </prompt>nixos-version
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17.09pre104379.6e0b727 (Hummingbird)
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<prompt>$ </prompt>git checkout -b local 6e0b727
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</screen>
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Or, to base your local branch on the latest version available in a NixOS
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channel:
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<screen>
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<prompt>$ </prompt>git remote update channels
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<prompt>$ </prompt>git checkout -b local channels/nixos-17.03
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</screen>
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(Replace <literal>nixos-17.03</literal> with the name of the channel you want
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to use.) You can use <command>git merge</command> or <command>git
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rebase</command> to keep your local branch in sync with the channel, e.g.
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<screen>
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<prompt>$ </prompt>git remote update channels
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<prompt>$ </prompt>git merge channels/nixos-17.03
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</screen>
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You can use <command>git cherry-pick</command> to copy commits from your
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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, you need to
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tell <command>nixos-rebuild</command> about them using the
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<option>-I</option> flag:
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<screen>
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<prompt># </prompt>nixos-rebuild switch -I nixpkgs=<replaceable>/my/sources</replaceable>/nixpkgs
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</screen>
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</para>
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<para>
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If you want <command>nix-env</command> to use the expressions in
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<replaceable>/my/sources</replaceable>, use <command>nix-env -f
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<replaceable>/my/sources</replaceable>/nixpkgs</command>, or change the
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default by adding a symlink in <filename>~/.nix-defexpr</filename>:
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<screen>
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<prompt>$ </prompt>ln -s <replaceable>/my/sources</replaceable>/nixpkgs ~/.nix-defexpr/nixpkgs
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</screen>
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You may want to delete the symlink
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<filename>~/.nix-defexpr/channels_root</filename> to prevent root’s NixOS
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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 default
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state, you may just remove the <filename>~/.nix-defexpr</filename> directory
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completely, log out and log in again and it should have been recreated with a
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link to the root channels.
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</para>
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<!-- FIXME: not sure what this means.
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<para>You should not pass the base directory
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<filename><replaceable>/my/sources</replaceable></filename>
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to <command>nix-env</command>, as it will break after interpreting expressions
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in <filename>nixos/</filename> as packages.</para>
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-->
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</chapter>
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