# Hacking

This section provides some notes on how to hack on Hydra. To get the
latest version of Hydra from GitHub:

```console
$ git clone git://github.com/NixOS/hydra.git
$ cd hydra
```

To enter a shell in which all environment variables (such as `PERL5LIB`)
and dependencies can be found:

```console
$ nix-shell
```

To build Hydra, you should then do:

```console
[nix-shell]$ ./bootstrap
[nix-shell]$ configurePhase
[nix-shell]$ make
```

You start a local database, the webserver, and other components with
foreman:

```console
$ foreman start
```

You can run just the Hydra web server in your source tree as follows:

```console
$ ./src/script/hydra-server
```

You can run Hydra's test suite with the following:

```console
[nix-shell]$ make check
[nix-shell]$ # to run as many tests as you have cores:
[nix-shell]$ make check YATH_JOB_COUNT=$NIX_BUILD_CORES
[nix-shell]$ # or run yath directly:
[nix-shell]$ yath test
[nix-shell]$ # to run as many tests as you have cores:
[nix-shell]$ yath test -j $NIX_BUILD_CORES
```

When using `yath` instead of `make check`, ensure you have run `make`
in the root of the repository at least once.

**Warning**: Currently, the tests can fail
if run with high parallelism [due to an issue in
`Test::PostgreSQL`](https://github.com/TJC/Test-postgresql/issues/40)
causing database ports to collide.

## Working on the Manual

By default, `foreman start` runs mdbook in "watch" mode. mdbook listens
at [http://localhost:63332/](http://localhost:63332/), and
will reload the page every time you save.

## Building

To build Hydra and its dependencies:

```console
$ nix-build release.nix -A build.x86_64-linux
```

## Development Tasks

### Connecting to the database

Assuming you're running the default configuration with `foreman start`,
open an interactive session with Postgres via:

```console
$ psql --host localhost --port 64444 hydra
```

### Runinng the builder locally

For `hydra-queue-runner` to successfully build locally, your
development user will need to be "trusted" by your Nix store.

Add yourself to the `trusted_users` option of `/etc/nix/nix.conf`.

On NixOS:

```nix
{
  nix.trustedUsers = [ "YOURUSER" ];
}
```

Off NixOS, change `/etc/nix/nix.conf`:

```conf
trusted-users = root YOURUSERNAME
```