• https://systemd.io/
• https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/9/html/using_systemd_unit_files_to_customize_and_optimize_your_system/assembly_working-with-systemd-unit-files_working-with-systemd#con_introduction-to-unit-files_assembly_working-with-systemd-unit-files
• https://www.freedesktop.org/software/systemd/man/latest/
• https://tadeubento.com/2023/systemd-hidden-gems-for-a-better-linux/

Systemd does a lot of stuff I guess it is easier to just lean based on what comes up / you need. There isn't a single path.

Next up: Learn how to create .service file, you may be able to use it from the template provided.

Then learn about target and unit

Find these on Youtube

The official website has ton of documentation and external links: https://systemd.io/

• Credentials
• Desktop Environment Integration
• Portable Services Introduction
• ... and more
• Arch Linux wiki
• Debian wiki
• Gentoo wiki
• Ubuntu wiki

And here some tutorials:

• https://systemd-by-example.com/ - a tutorial with interactive examples

The best crash course I received was when I needed to translate my startup scripts into systemd services. The hands-on learning was priceless.

The arch wiki is always a good place to check for these sorts of things, whether or not you use arch btw.

The man pages.

Write a couple of your own toy services as practice. Write a one-shot that fires at a particular time during boot, a normal service that would run a daemon and a mount service that fires after its dependencies are loaded (like, say, a bind mount that sets up a directory under /run/foo after the backing filesystem is mounted - I do this to make fast ext4 storage available in some parts of the VFS tree while using a btrfs filesystem for everything else.) You can also write file watcher services that fire after changes to a file or directory, I use one of those to mirror /boot/ to /.boot/ on another filesystem so it's captured by my system snapshots.

I'd start by reading the docs so you have some ideas about what services can do, then you'll find uses that you wouldn't have thought of before.