systemd/docs/CONTRIBUTING.md

title	category	layout	SPDX-License-Identifier
Contributing	Contributing	default	LGPL-2.1-or-later

Contributing

We welcome contributions from everyone. However, please follow the following guidelines when posting a GitHub Pull Request or filing a GitHub Issue on the systemd project:

Filing Issues

• We use GitHub Issues exclusively for tracking bugs and feature requests (RFEs) of systemd. If you are looking for help, please contact systemd-devel mailing list instead.
• We only track bugs in the two most recently released (non-rc) versions of systemd in the GitHub Issue tracker. If you are using an older version of systemd, please contact your distribution's bug tracker instead (see below). See GitHub Release Page for the list of most recent releases.
• When filing a feature request issue (RFE), please always check first if the newest upstream version of systemd already implements the feature, and whether there's already an issue filed for your feature by someone else.
• When filing an issue, specify the systemd version you are experiencing the issue with. Also, indicate which distribution you are using.
• Please include an explanation how to reproduce the issue you are pointing out.

Following these guidelines makes it easier for us to process your issue, and ensures we won't close your issue right-away for being misfiled.

Older downstream versions

For older versions that are still supported by your distribution please use respective downstream tracker:

• Fedora - bugzilla
• RHEL/CentOS - bugzilla or systemd-rhel github
• Debian - bugs.debian.org

Security vulnerability reports

See reporting of security vulnerabilities.

Posting Pull Requests

• Make sure to post PRs only relative to a recent tip of the main branch.
• Follow our Coding Style when contributing code. This is a requirement for all code we merge.
• Please make sure to test your change before submitting the PR. See the Hacking guide for details on how to do this.
• Make sure to run the test suite locally, before posting your PR. We use a CI system, meaning we don't even look at your PR, if the build and tests don't pass.
• If you need to update the code in an existing PR, force-push into the same branch, overriding old commits with new versions.
• After you have pushed a new version, add a comment. If you are a member of the systemd project on GitHub, remove the reviewed/needs-rework label.
• If you are copying existing code from another source (eg: a compat header), please make sure the license is compatible with LGPL-2.1-or-later. If the license is not LGPL-2.1-or-later, please add a note to LICENSES/README.md.
• If the pull request stalls without review, post a ping in a comment after some time has passed. We are always short on reviewer time, and pull requests which haven't seen any recent activity can be easily forgotten.

Final Words

We'd like to apologize in advance if we are not able to process and reply to your issue or PR right-away. We have a lot of work to do, but we are trying our best!

Thank you very much for your contributions!

Backward Compatibility And External Dependencies

We strive to keep backward compatibility where possible and reasonable. The following are general guidelines, not hard rules, and case-by-case exceptions might be applied at the discretion of the maintainers. The current set of build time and runtime dependencies are documented in the README.

New features

It is fine for new features/functionality/tools/daemons to require bleeding edge external dependencies, provided there are runtime and build time graceful fallbacks (e.g.: daemon will not be built, runtime functionality will be skipped with clear log message). In case a new feature is added to both systemd and one of its dependencies, we expect the corresponding feature code to be merged upstream in the dependency before accepting our side of the implementation. Making use of new kernel syscalls can be achieved through compat wrappers in our tree (see: src/basic/missing_syscall_def.h), and does not need to wait for glibc support.

External Build/Runtime Dependencies

It is often tempting to bump external dependencies minimum versions to cut cruft, and in general it's an essential part of the maintenance process. But as a generic rule, existing dependencies should not be bumped without very strong reasons. When possible, we try to keep compatibility with the most recent LTS releases of each mainstream distribution for optional components, and with all currently maintained (i.e.: not EOL) LTS releases for core components. When in doubt, ask before committing time to work on contributions if it's not clear that cutting support would be obviously acceptable.

Kernel Requirements

Same principles as with other dependencies should be applied. It is fine to require newer kernel versions for additional functionality or optional features, but very strong reasons should be required for breaking compatibility for existing functionality, especially for core components. It is not uncommon, for example, for embedded systems to be stuck on older kernel versions due to hardware requirements, so do not assume everybody is running with latest and greatest at all times. In general, currently maintained LTS branches should keep being supported for existing functionality, especially for core components.

libsystemd.so

libsystemd.so is a shared public library, so breaking ABI/API compatibility creates a lot of work for its users, and should always be avoided apart from the most extreme circumstances. For example, always add a new interface instead of modifying the signature of an existing function. It is fine to mark an interface as deprecated to gently nudge users toward a newer one, but in general support for the old one should be maintained whenever possible. Symbol versioning and the compiler's deprecated attribute should be used when managing the lifetime of a public interface.

libudev.so

libudev.so is a shared public library, and is still maintained, but should not gain new symbols at this point.