systemd-crontab-generator

What's it?

This is a compatibility layer for crontab-to-systemd timers framework. It works by parsing crontab and anacrontab files from usual places like /etc/crontab and /var/spool/cron and generating systemd timers and services. You can use cron.target as a single control point for the generated units.

It's intented to be drop-in replacement for all cron implementations.

Rationale

The crontab generator for systemd (implemented in C) was already published on maillist, but was later declined by Lennart:

I am not convinced this is a really good idea. From my perspective at least it appears that we should much rather just convert the crontabs and that's it. Unlike sysv init scripts the number of crontab in use (at least on Fedora) is relatively small, and very rare in third-party packages.

Lennart

While I'm generally agree with him, I'm not totally convinced it's always convinient to herd a bunch of separate *.timer and *.service files. I find convinient to have all jobs schedule in one single file, and it's more obvious to see relations in jobs scheduling if you have several jobs on sight at once.

All things considered, I think people should have an alternative here, so I decided to support the idea of systemd crontab generator. Though the original C implementation of crontab parser from maillist is very incomplete: it doesn't support monotonic schedules (like @daily or @yearly), it can't parse comments and environment variable settings, etc.

I'm not very good in C, so C implementation (while it's recommended for generators) whould take me ages to write, so I used Python for proof-of-concept implementation. And here comes systemd-crontab-generator.

Installation

If you are on Archlinux, install from AUR, otherwise see PKGBUILD file and execute commands from package() sub.

Usage

The generator runs on system boot. If you change your crontabs in runtime, run systemd-crontab-update script as root (sudo systemd-crontab-update) to regenerate systemd units and reload them.

The project includes simple crontab command equivalent, which behaves like standard crontab command (and accepts the same main options), and runs systemd-crontab-update command after user crontab file update. Note, though, the systemd-crontab-update requires superuser priviledges, so crontab tries to run it under sudo, so if you are not allowed to run systemd-crontab-update via /etc/sudoers file, you can't update crontab timers.

To control cron jobs, use cron.target, e.g. to start and enable cron after installation:

# systemctl enable cron.target
# systemctl start cron.target

Disclaimer

This is not a production-ready project! Use at your own risk! I'm not responsible for any data losses, time losses, money losses or any other failures due to usage of this project! You were warned!

License

The project is licensed under GPLv3. Don't forget to attribute if you derive from my work!

Contribution

You are most welcome to post bugs and PRs! Also check out comments in AUR for current news about Arch package status.