Coding and Building

Let's walk through contributing to the Redox subpackage games, which is a collection of low-def games. We are going to modify minesweeper to display P instead of F on flagged spots.

(Before reading this page you must read the Understanding Cross-Compilation for Redox and Build System Quick Reference pages)

Working with Git

Before starting development, read through Creating Proper Pull Requests, which describes how the Redox team uses Git.

In this example, we will discuss creating a fork of the games package, pretending you are going to create a Merge Request for your changes. Don't actually do this. Only create a fork when you have a permanent change you want to contribute to Redox.

Anonymous commits

If you are new to Git, it request your username and email before the first commit on some offline repository, if you don't want to insert your personal information, run:

  • Repository
cd your-repository-folder
git config 'Anonymous'
git config '<>'

This command will make you anonymous only on this repository.

  • Global
git config --global 'Anonymous'
git config --global '<>'

This command will make you anonymous in all repositories of your user.

Using Multiple Windows

For clarity and ease of use, we will be using a couple of Terminal windows on your host system, each running a different bash shell instance.

  1. The Build shell, normally at ~/tryredox/redox or whatever your base redox directory is.
  2. The Coding shell, normally at ~/tryredox/redox/cookbook/recipes/games/source.

Set up your Configuration

To get started, follow the steps in Including a Program in a Redox Build to include the games package in your myfiles configuration file. In your Terminal window, go to your redox base directory and run:

make qemu

On Redox, run minesweeper as described in the link above. Type the letter f and you will see F appear on your screen. Use Ctrl-Alt-G to regain control of your cursor, and click the upper right corner to exit QEMU.

Keep the Terminal window open. That will be your Build shell.

The Recipe

The games package is built in the folder cookbook/recipes/games. When you clone the redox base package, it includes a file cookbook/recipes/games/recipe.toml. The recipe tells the toolchain how to get the source and how to build it.

When you build the system and include the games package, the toolchain does a git clone into the directory cookbook/recipes/games/source. Then it builds the package in the directory cookbook/recipes/games/target.

Edit the recipe so it does not try to automatically clone the sources.

  • Create a Terminal window running bash on your host system, which we will call your Coding shell.
  • Change to the games directory.
  • Open recipe.toml in an editor.
cd ~/tryredox/redox/cookbook/recipes/games
gedit recipe.toml &
  • Comment out the [source] section at the top of the file.
# [source]
# git = ""
  • Save your changes.

Git Clone

To set up this package for contributing, do the following in your Coding shell.

  • Delete the source and target directories in cookbook/recipes/games.
  • Clone the package into the source directory, either specifying it in the git clone or by moving it after clone.
rm -rf source target
git clone --origin upstream --recursive
mv games source
  • If you are making a permanent change that you want to contribute, (you are not, don't actually do this) at this point you should follow the instructions in Creating Proper Pull Requests, replacing redox.git with games.git. Make sure you fork the correct repository, in this case redox-os/games. Remember to create a new branch before you make any changes.

  • If you want to Git Clone a remote repoitory (main repoitory/your fork), you can add these sections on your recipe.toml:

git = your_git_link
branch = your_branch (optional)

Edit your Code

  • Using your favorite code editor, make your changes. We use gedit in this example, from your Coding shell. You can also use VS Code.
cd source
gedit src/minesweeper/ &
  • Search for the line containing the definition of the FLAGGED constant (around line 36), and change it to P.
const FLAGGED: &'static str = "P";

Check your Code on Linux

Most Redox applications are source-compatible with Linux without being modified. You can (and should) build and test your program on Linux.

  • From within the Coding shell, go to the source directory and use the Linux version of cargo to check for errors.
cargo check

(Since much of the code in games is older (pre-2018 Rust), you will get several warnings. They can be ignored)

You could also use cargo clippy, but minesweeper is not clean enough to pass.

  • The games package creates more than one executable, so to test minesweeper on Linux, you need to specify it to cargo. In the source directory, do:
cargo run --bin minesweeper

The Full Rebuild Cycle

After making changes to your package, you should make rebuild, which will check for any changes to packages and make a new Redox image. make all and make qemu do not check for packages that need to be rebuilt, so if you use them, your changes may not be included in the system. Once you are comfortable with this process, you can try some tricks to save time.

  • Within your Build shell, in your redox directory, do:
script build.log
make rebuild

The script command starts a new shell and logs all the output from the make command.

The exit command is to exit from script. Remember to exit the script shell to ensure all log messages are written to build.log. There's also a trick to flush the log.

  • You can now scan through build.log to check for errors. The file is large and contains many ANSI Escape Sequences, so it can be hard to read. However, if you encountered a fatal build error, it will be at the end of the log, so skip to the bottom and scan upwards.

Test Your Changes

In the Redox instance started by make qemu, test your changes to minesweeper.

  • Log in with user user and no password.
  • Open a Terminal window.
  • Type minesweeper.
  • Use your arrow keys or WSAD to move to a square and type f to set a flag. The character P will appear.

Congratulations! You have modified a program and built the system! Next, create a bootable Redox with your change.

  • If you are still running QEMU, type Ctrl-Alt-G and click the upper right corner of the Redox window to exit.
  • In your Build shell, in the redox directory, do:
make live

In the directory build/x86_64/myfiles, you will find the file livedisk.iso. Follow the instructions for Running on Real Hardware and test out your change.

Test Your Changes (out of the Redox build system)

Redoxer is the tool used to build/run Rust programs (and C/C++ programs with zero dependencies) for Redox, it download the Redox toolchain and make Cargo use it.


  • cargo install redoxer - install redoxer tool.
  • redoxer toolchain - install redoxer toolchain.
  • redoxer build - build project with redoxer.
  • redoxer run - run project with redoxer.
  • redoxer test - test project with redoxer.
  • redoxer exec echo hello - run arbitrary executable with redoxer.

Update crates

Search Text On Files

To find which package contains a particular command, crate or function call, you can use the grep command.

This will speed up your development workflow.

  • Command examples
grep -rnw "redox-syscall" --include "Cargo.toml"

This command will find any "Cargo.toml" file that contains the phrase "redox-syscall". Helpful for finding which package contains a command or uses a crate.

grep -rni "physmap" --include "*.rs"

This command will find any ".rs" file that contains the string "physmap". Helpful for finding where a function is used or defined.

Options context:

  • -n - display the line number of the specified text on each file.

  • -r - Search directories recursively.

  • -w - Match only whole words.

  • -i - Ignore case distinctions in patterns and data.

  • grep explanation - GeeksforGeeks article explaining the grep program.

Checking In your Changes

Don't do this now, but if you were to have permanent changes to contribute to a package, at this point, you would git push and create a Merge Request, as described in Creating Proper Pull Requests.

If you were contributing a new package, such as porting a Rust application to Redox, you would need to check in the recipe.toml file. It goes in the cookbook subproject. You may also need to modify a filesystem config file, such as config/demo.toml. It goes in the redox project. You must fork and do a proper Pull Request for each of these projects. Please coordinate with the Redox team via Chat before doing this.

Shortening the Rebuild Cycle

To skip some of the steps in a full rebuild, here are some tricks.

Build your Package for Redox

You can build just the games package, rather than having make rebuild check every package for changes. This can help shorten the build cycle if you are trying to resolve issues such as compilation errors or linking to libraries.

  • In your Build shell, in the redox directory, type:

Redox's makefiles have a rule for r.PACKAGE, where PACKAGE is the name of a Redox package. It will make that package, ready to load into the Redox filesystem.

Once your Redox package has been successfully built, you can use make rebuild to create the image, or, if you are confident you have made all packages successfully, you can skip a complete rebuild and just make a new image.

If you had a problem, use this command to log any possible errors on your terminal output:

make c.recipe-name r.recipe-name 2>&1 | tee recipe-name.log

Make a New QEMU Image

Now that all the packages are built, you can make a Redox image without the step of checking for modifications.

  • In your Build shell, in the redox directory, do:
make image
make qemu


make image qemu
  • make image skips building any packages (assuming the last full make succeeded), but it ensures a new image is created, which should include the package you built in the previous step.

Most Quick Trick To Test Changes


make c.recipe-name
make r.recipe-name
make image
make qemu


make c.recipe-name r.recipe-name image qemu

This command will build just your modified recipe, then update your QEMU image with your modified recipe and run QEMU with a GUI.

Insert Files On QEMU Image

If you feel the need to skip creating a new image, and you want to directly add a file to the existing Redox image, it is possible to do so. However, this is not recommended. You should use a recipe to make the process repeatable. But here is how to access the Redox image as if it were a Linux filesystem.

  • NOTE: You must ensure that Redox is not running in QEMU when you do this.

  • In your Build shell, in the redox directory, type:

make mount

The Redox image is now mounted as a directory at build/x86_64/myfiles/filesystem.

  • Remove the old minesweeper and replace it with your new version. In the Build shell.
cd ~/tryredox/redox/build/x86_64/myfiles/filesystem
rm ./bin/minesweeper
cp ~/tryredox/redox/cookbook/recipes/games/target/x86_64-unknown-redox/stage/bin/minesweeper ./bin
  • Unmount the filesystem and test your image. NOTE: You must unmount before you start QEMU.
cd ~/tryredox/redox
make unmount
make qemu

The new version of minesweeper is now in your Redox filesystem.

Insert Text Files On Redox QEMU

If you need to move text files, such as shell scripts or command output, from or to your Redox instance running on QEMU, use your Terminal window that you used to start QEMU. To capture the output of a Redox command, run script before starting QEMU.

script qemu.log
make qemu
redox login: user
# execute your commands, with output to the terminal
# exit QEMU
# exit the shell started by script

The command output will now be in the file qemu.log. Note that if you did not exit the script shell, the output may not be complete.

To transfer a text file, such as a shell script, onto Redox, use the Terminal window with copy/paste.

redox login: user
cat > << EOF
# Copy the text to the clipboard and use the Terminal window paste

If your file is large, or non-ascii, or you have many files to copy, you can use the process described in Patch an Image. However, you do so at your own risk.

Files you create while running QEMU remain in the Redox image, so long as you do not rebuild the image. Similarly, files you add to the image will be present when you run QEMU, so long as you do not rebuild the image.

Make sure you are not running QEMU. Run make mount. You can now use your file browser to navigate to build/x86_64/myfiles/filesystem. Copy your files into or out of the Redox filesystem as required. Make sure to exit your file browser window, and use make unmount before running make qemu.

Note that in some circumstances, make qemu may trigger a rebuild (e.g. make detects an out of date file). If that happens, the files you copied into the Redox image will be lost.

Working with an unpublished version of a crate

Some recipes use Cargo dependencies (Cargo.toml) with recipe dependencies (recipe.toml), if you are making a change to one of these Cargo dependencies, your merged changes will take a while to appear on as we publish to there instead of using our GitLab fork.

To test your changes quickly, follow these tutorials on Cargo documentation:

A Note about Drivers

Drivers are a special case for rebuild. The source for drivers is fetched both for the drivers recipe and the drivers-initfs recipe. The initfs recipe also copies some drivers from drivers-initfs during the build process. If your driver is included in initfs, you need to keep all three in sync. The easiest solution is to write a build shell script something like the following, which should be run in your redox base directory. (Note: This assumes your driver code edits are in the directory cookbook/recipes/drivers. Don't accidentally remove your edited code.)

rm -rf cookbook/recipes/drivers-initfs/{source,target} cookbook/recipes/initfs/target
cp -R cookbook/recipes/drivers/source cookbook/recipes/drivers-initfs
make rebuild
make qemu

Development Tips

  • Make sure your build system is up-to-date, read this section in case of doubt.
  • If some program can't build or work properly, remember that something could be missing/hiding on relibc, some function or bug.
  • If you have some error on QEMU, remember to test different settings or check your operating system (Debian, Ubuntu and Pop OS! are the recommend Linux distributions to do testing/development for Redox).
  • Remember to log all errors, you can use this command as example:
your-command 2>&1 | tee file-name.log
  • If you have a problem that seems to not have a solution, think on simple/stupid things, sometimes you are very confident on your method and forget obvious things (it's very common).
  • If you want a more quick review of your Merge Request, make it small, Jeremy will read it more fast.
  • If your big Merge Request is taking too long to merge try to shrink it with other small MRs, make sure it don't break anything, if this method break your changes, don't shrink.

VS Code Tips and Tricks

Although not for every Rustacean, VS Code is helpful for those who are working with unfamiliar code. We don't get the benefit of all its features, but the Rust support in VS Code is very good.

If you have not used VS Code with Rust, here's an overview. VS Code installation instructions are here.

After installing the rust-analyzer extension as described in the overview, you get access to several useful features.

  • Inferred types and parameter names as inline hints.
  • Peeking at definitions and references.
  • Refactoring support.
  • Autoformat and clippy on Save (optional).
  • Visual Debugger (if your code can run on Linux).
  • Compare/Revert against the repository with the Git extension.

Using VS Code on individual packages works pretty well, although it sometimes take a couple of minutes to kick in. Here are some things to know.

Start in the "source" folder

In your Coding shell, start VS Code, specifying the source directory.

code ~/tryredox/redox/cookbook/recipes/games/source

Or if you are in the source directory, just code . with the period meaning the source dir.

Add it to your "Favorites" bar

VS Code remembers the last project you used it on, so typing code with no directory or starting it from your Applications window or Favorites bar will go back to that project.

After starting VS Code, right click on the icon and select Add to Favorites.

Wait a Couple of Minutes

You can start working right away, but after a minute or two, you will notice extra text appear in your Rust code with inferred types and parameter names filled in. This additional text is just hints, and is not permanently added to your code.

Save Often

If you have made significant changes, rust-analyzer can get confused, but this can usually be fixed by doing Save All.

Don't Use it for the whole of Redox

VS Code cannot grok the gestalt of Redox, so it doesn't work very well if you start it in your redox base directory. It can be handy for editing recipes, config and make files. And if you want to see what you have changed in the Redox project, click on the Source Control icon on the far left, then select the file you want to compare against the repository.

Don't Build the System in a VS Code Terminal

In general, it's not recommended to do a system build from within VS Code. Use your Build window. This gives you the flexibility to exit Code without terminating the build.