---
title: builds.sr.ht Configuration
---

This document covers the configuration process for builds.sr.ht.

# Security Model

Let's start with a brief overview of the security model of builds.sr.ht.
Since builds.sr.ht runs arbitrary user code (and allows users to utilize
root), it's important to carefully secure the build environments.

To that end, our build jobs run in a sandbox that consists of:

- A [KVM](https://www.linux-kvm.org) virtual machine (via
  [QEMU](https://www.qemu.org)), which
- runs inside of an otherwise empty Docker image, which
- runs as an unprivledged user on
- a server that is physically separate from anything important, uses its own
  isolated Redis instance, and has minimal database access.

We suggest you take similar precautions if your servers may run untrusted
builds.

<div class="alert alert-warning">
  <strong>Warning:</strong> Even if you only build your own software,
  integration with other services may cause you to run untrusted builds (e.g.
  automatic testing of patches via lists.sr.ht).
</div>

# Master Server

## Web Service

The master server requires *two* Redis servers – one that runners should have
access to, and one that they should not have access to. For the former,
insert connection details into build.sr.ht's configuration file under the `redis`
key.

Each runner also requires a local Redis instance running.

<div class="alert alert-info">
  <strong>Note:</strong> In a deployment where all services are on the same
  server, running only trusted builds, you can get away with a single Redis
  instance.
</div>

# Database

Create two users, one for the master and one for the runners (or one for each
runner if you prefer). They need the following permissions:

- **master** should have ownership over the database and full read/write/alter
  access to all table
- **runner** should have read/write access to the job, artifact and task tables,
  and read access to the user and secrets tables.

If you are running the master and runners on the same server, you will only be
able to use one user — the master user. Configure both the web service and build
runner with this account. Otherwise, two separate accounts is recommended.

Note: in the future runners will not have database access.

# Install images

On the runner, install the `builds.sr.ht-images` package (if building from
source, this package is simply the `images` directory copied to
`/var/lib/images`), as well as docker. Build the docker image like so:

    $ cd /var/lib/images
    $ docker build -t qemu -f qemu/Dockerfile .

This will build a docker image named `qemu` which contains a statically linked
build of qemu and nothing else.

## Bootstrapping our images

A `genimg` script is provided for each image which can be run from a working
image of that guest to produce a new image. You need to manually prepare a
working guest of each image type (that is, to build the Arch Linux image you
need a working Arch Linux installation to bootstrap from). Then you can run
the provided `genimg` to produce the disk image. You should read the genimg
script to determine what dependencies need to be installed before it can be
run to completion.

The directory structure for bootable images should have the format
images/$distro/$release/$arch/ with the root.img.qcow2 file within the $arch
directory.

A `build.yml` file is also provided for each image to build itself on your
build infrastructure once you have it set up, which you should customize as
necessary. It's recommended that you set up cron jobs to build fresh images
frequently — a script at `contrib/submit_image_build` is provided for this
purpose.

**Note**: it is recommended that you modify our `build.yml` files to suit your
instance's needs, then run it on *our* hosted builds.sr.ht instance to bootstrap
your images. This is the fastest and most convenient way to bootstrap the images
you need.

**Note**: You will need nested virtualization enabled in order to build images
from within a pre-existing build image (i.e. via the `build.yml` file). If you
run into issues with `modprobe kvm_intel` within the genimg script, you can fix
this by removing the module and then re-inserting it with `insmod kvm_intel.ko
nested=1` in the directory containing the kernel module.

## Creating new images

If you require additional images, study the `control` script to understand how
the top-level boot process works. You should then prepare a disk image for your
new system (name it `root.img.qcow2`) and write a `functions` file. The only
required function is `boot`, which should call `_boot` with any additional
arguments you want to pass to qemu. If your image will boot up with no
additional qemu arguments, this function will likely just call `_boot`. You can
optionally provide a number of other functions in your `functions` file to
enable various features:

- To enable installing packages specified in the build manifest, write an
  `install` function with the following usage:
  `install [ssh port] [packages...]`
- To enable adding third-party package repositories, write an `add_repository`
  function: `add_repository [ssh port] [name] [source]`. The `source` is usually
  vendor-specific, you can make this any format you want to encode repo URLs,
  package signing keys, etc.

In order to run builds, we require the following:

- The disk should be able to boot itself up, make sure to install a bootloader
  and set up partitions however you like.
- Networking configured with IPv4 address `10.0.2.15/25` and gateway `10.0.2.2`.
  Don't forget to configure DNS, too.
- SSH listening on port 22 (the standard port) with passwordless login *enabled*
- A user named `build` to log into SSH with, preferrably with uid 1000
- git config setting user.name to builds.sr.ht and user.email to builds@sr.ht
- Bash (temporary — we'll make this more generic at some point)

Not strictly necessary, but recommended:

- Set the hostname to `build`
- Configure NTP and set the timezone to UTC
- Add the build user to the sudoers file with `NOPASSWD: ALL`
- In your `functions` file, set `poweroff_cmd` to a command we can SSH into the
  box and use to shut off the machine. If you don't, we'll just kill the qemu
  process.
- It is also recommended to write a `sanity_check` function which takes no
  arguments, but boots up the image and runs any tests necessary to verify
  everything is working and return a nonzero status code if not.

You will likely find it useful to read the scripts for existing build images as
a reference. Once you have a new image, email the scripts to
[`~sircmpwn/sr.ht-dev@lists.sr.ht`](https://lists.sr.ht/~sircmpwn/sr.ht-dev) so
we can integrate them upstream!

# Additional configuration

Write an `/etc/sr.ht/config.ini` configuration file similar to the one you wrote
on the master server. Only the `[sr.ht]` and `[builds.sr.ht]` sections are
required for the runners. `images` should be set to the installation path of
your images (`/var/lib/images`) and `buildlogs` should be set to the path where
the runner should write its build logs (the runner user should be able to create
files and directories here). Set `runner` to the hostname of the build runner.
You will need to configure nginx to serve the build logs directory at
http://RUNNER-HOSTNAME/logs/ in order for build logs to appear correctly on the
website.

Once all of this is done, make sure the worker is compiled (with go 1.11 or
later) by running `go build` in the worker/ directory, start the
`builds.sr.ht-worker` service and it's off to the races. Submit builds on the
master server and they should run correctly at this point.

For SSH access to (failed) builds you will need to install `git.sr.ht` and
configure `[git.sr.ht::dispatch]` for `buildsrht-keys`.