pyrox.dev
1# Getting the Sources {#sec-getting-sources}
2
3By default, NixOS's `nixos-rebuild` command uses the NixOS and Nixpkgs
4sources provided by the `nixos` channel (kept in
5`/nix/var/nix/profiles/per-user/root/channels/nixos`). To modify NixOS,
6however, you should check out the latest sources from Git. This is as
7follows:
8
9```ShellSession
10$ git clone https://github.com/NixOS/nixpkgs
11$ cd nixpkgs
12$ git remote update origin
13```
14
15This will check out the latest Nixpkgs sources to `./nixpkgs` the NixOS
16sources to `./nixpkgs/nixos`. (The NixOS source tree lives in a
17subdirectory of the Nixpkgs repository.) The `nixpkgs` repository has
18branches that correspond to each Nixpkgs/NixOS channel (see
19[](#sec-upgrading) for more information about channels). Thus, the
20Git branch `origin/nixos-17.03` will contain the latest built and tested
21version available in the `nixos-17.03` channel.
22
23It's often inconvenient to develop directly on the master branch, since
24if somebody has just committed (say) a change to GCC, then the binary
25cache may not have caught up yet and you'll have to rebuild everything
26from source. So you may want to create a local branch based on your
27current NixOS version:
28
29```ShellSession
30$ nixos-version
3117.09pre104379.6e0b727 (Hummingbird)
32
33$ git checkout -b local 6e0b727
34```
35
36Or, to base your local branch on the latest version available in a NixOS
37channel:
38
39```ShellSession
40$ git remote update origin
41$ git checkout -b local origin/nixos-17.03
42```
43
44(Replace `nixos-17.03` with the name of the channel you want to use.)
45You can use `git merge` or `git
46 rebase` to keep your local branch in sync with the channel, e.g.
47
48```ShellSession
49$ git remote update origin
50$ git merge origin/nixos-17.03
51```
52
53You can use `git cherry-pick` to copy commits from your local branch to
54the upstream branch.
55
56If you want to rebuild your system using your (modified) sources, you
57need to tell `nixos-rebuild` about them using the `-I` flag:
58
59```ShellSession
60# nixos-rebuild switch -I nixpkgs=/my/sources/nixpkgs
61```
62
63If you want `nix-env` to use the expressions in `/my/sources`, use
64`nix-env -f
65 /my/sources/nixpkgs`, or change the default by adding a symlink in
66`~/.nix-defexpr`:
67
68```ShellSession
69$ ln -s /my/sources/nixpkgs ~/.nix-defexpr/nixpkgs
70```
71
72You may want to delete the symlink `~/.nix-defexpr/channels_root` to
73prevent root's NixOS channel from clashing with your own tree (this may
74break the command-not-found utility though). If you want to go back to
75the default state, you may just remove the `~/.nix-defexpr` directory
76completely, log out and log in again and it should have been recreated
77with a link to the root channels.