# 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`)
are set up so that those 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
```