gem5 website

The website for gem5 is written in Jekyll markdown. It serves as the primarily source of information for those interested in the gem5 project. In the spirit of gem5's community-led, open governance model, anyone who wishes may make contributions and improvements to the website. This README outlines the basic procedure to do so, as well as notes the directory structure and general guidelines.


You may clone the repository, and run a local instance of the website using:

git clone
cd gem5-website
jekyll serve --config _config.yml,_config_dev.yml

The jekyll server may also be run using:

bundle exec jekyll serve --config _config.yml,_config_dev.yml

Changes may be made and committed using:

git add <changed files>
git commit

The commit message must adhere to our style. The first line of the commit is the “header”. The header line must not exceed 65 characters and adequately describe the change. To be consistent with commits made to the gem5 gerrit, the header should start with a website tag followed by a colon.

After this, a more detailed description of the commit can be included. This is inserted below the header, separated by an empty line. Including a description is optional but strongly recommended for complex changes. The description may span multiple lines, and multiple paragraphs. No line in the description may exceed 72 characters. We also recommend adding reference to any relevant Jira issue (from the gem5 Jira: so the context of a change can be more easily understood.

Below is an example of how a gem5 website commit message should be formatted:

website: This is an example header

This is a more detailed description of the commit. This can be as long as
is necessary to adequately describe the change.

A description may spawn multiple paragraphs if desired.


Submitting a contribution

We utilize Gerrit to review changes made to the website. Once changes are committed to a local repository they may be submitted for review by executing:

git push origin HEAD:refs/for/stable

At this stage you may receive an error if you're not registered to contribute to our Gerrit. To resolve this issue:

  1. Create an account at
  2. Go to User Settings
  3. Select Obtain password (under HTTP Credentials).
  4. A new tab shall open, explaining how to authenticate your machine to make contributions to Gerrit. Follow these instructions and try pushing again.

Gerrit will amend your commit message with a Change-ID. Any commit pushed to Gerrit with this Change-ID is assumed to be part of this change.

Code Review

Once a change has been submitted to Gerrit, you may view the change at under Your -> Changes -> Outgoing reviews).

Through the Gerrit prowl we strongly advise you add reviewers to your change. Gerrit will automatically notify those you assign. We recommend you add both Bobby R. Bruce and Jason Lowe-Power as reviewers.

Reviewers will review the change. For non-trivial edits, it is not unusual for a change to receive feedback from reviewers that they want incorporated before flagging as acceptable for merging into the gem5 website repository. All communications between reviewers and contributors should be done in a polite manner. Rude and/or dismissive remarks will not be tolerated.

Once your change has been accepted by reviewers you will be able to click Submit within your changes Gerrit page. This focally merges the change into the gem5 website repository. The website will be automatically updated with your changes within 30 minutes.

Directory Structure


Yaml files, for easily editing navigation.


Page section and main navigation bar are here.


Different layout templates used on the site.

  • default: base layout
  • page: any regular page
  • toc: a page that requires table of contents
  • post: blog post page
  • documentation: documentation page


All pages (other than the index.html home page) should be placed in this folder. There is a subfolder /documentation where pages meant for the documentation part of the site can be kept. This is purely for organization and ease of finding things. Reorganizing the _pages folder should not affect the site.


Holds blog posts.


All custom css is kept in _layout.scss.


Images and javascript files.


Holds index.html of blog page.


To edit the navigation bar: Go to _includes/header.html Navigation element without submenu:

<li class="nav-item {% if page.title == "Home" %}active{% endif %}">
  <a class="nav-link" href="{{ "/" | prepend: site.baseurl }}">Home</a>

Replace Home in {% if page.title == "Home" %} to your page‘s title. Replace / in href="{{ "/" | prepend: site.baseurl }}" to the page’s permalink. Replace Home in >Home</a> with what you want the navbar to show.

Navigation element with submenu:

<li class="nav-item dropdown {% if page.parent == "about" %}active{% endif %}">
  <a class="nav-link dropdown-toggle" id="navbarDropdownMenuLink" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
  <div class="dropdown-menu" aria-labelledby="navbarDropdownMenuLink">
    <a class="dropdown-item" href="{{ "/about" | prepend: site.baseurl }}">About</a>
    <a class="dropdown-item" href="{{ "/publications" | prepend: site.baseurl }}">Publications</a>
    <a class="dropdown-item" href="{{ "/governance" | prepend: site.baseurl }}">Governance</a>

Replace about in {% if page.parent == "about" %} with a word that will represent the parent of all pages in the submenu. Make sure the frontmatter in those pages includes parent: [your_parent_identifier]. Replace the permalink and title in all the <a></a> submenu items.


Edit Documentation Navigation


Parent Topic:

  • subtopic
  • subtopic
  • ...

Parent Topic:

  • subtopic
  • ...

To edit the documentation navigation, simply edit the documentation.yml file in the _data folder. docs lists the parent topics, and within it subitems lists its subtopics. This is an example of how it should be formatted:

title: Documentation

  - title: Getting Started     # Parent Topic
    id: gettingstarted     # see below
    url: /gettingstarted     # see below
      - page: Introduction     # Name that will appear in navigation
        url: /introduction     # url
      - page: Dependencies
        url: /dependencies
  - title: Debugging     # Parent Topic
    id: debugging     # see below
      - page: Piece 1
        url: /piece1
      - page: Piece 2
        url: /piece2

Notes: id is an identifier that links subtopics to its parent. It is required and must not contain any spaces. The subtopic pages must include in the frontmatter parent: id with id being the parent's id.

url is optional for parent topics, if a parent topic has its own a page. If no url is provided, it will automatically link to the first subtopic.

Add New Page

To add a new documentation page, first add frontmatter at the top of either the markdown or html file to be added.

layout: documentation     // specify page layout
title: Getting Started     // title of the page
parent: gettingstarted     // see below
permalink: /gettingstarted/     // url


parent should be the exact same as the id of its parent topic that is assigned to it in _data/documentation.yml file. (If the page is the parent topic, parent is the same as the id assigned to it in _data/documentation.yml file.)

Place the file in _pages/documentation. Make sure to add the page to the documentation navigation, explained by the section above.

Indicating outdated information

To flag information in a page as valid, use an outdated notice in the .md file of that page:

{: .outdated-notice}
This page is outdated!

This will be replaced by a warning element containing the text “Note: This page is outdated.”, followed by the content succeeding the notice - in this case, “This page is outdated!”. In this way, you can add additional information explaining why or how the page is outdated, and general tips on what to do to mitigate this issue.


Make sure that the text following {: .outdated-notice} is not used as a title, heading, or any other important Markdown element, as it will be incorporated into the outdated notice and break formatting.


Add blog page to _posts folder. Page must be named in this format: At the top of the page add:

layout: post     // specify page layout
title: How to Debug
author: John
date: yyyy-mm-dd