Known Environment Variables A number of systemd components take additional runtime parameters via environment variables. Many of these environment variables are not supported at the same level as command line switches and other interfaces are: we don’t document them in the man pages and we make no stability guarantees for them. While they generally are unlikely to be dropped any time soon ...
Diagnosing Boot Problems If your machine gets stuck during boot, first check if the hang happens before or after control passes to systemd. Try to boot without rhgb and quiet on the kernel command line. If you see some messages like these: Welcome to Fedora VERSION (codename)!” Starting name … [ OK ] Started name. then systemd is running. (See an actual screenshot.) Debugging always gets ...
Optimizations without profiling are premature optimizations! Note that systemd’s fast performance is a side effect of its design but wasn’t the primary design goal. As it stands now systemd (and Fedora using it) has been optimized very little and still has a lot of room for improvements. There are still many low hanging fruits to pick!
Example: io.systemd.Unit.List outputs unit configuration, which can later be reused to create another unit via io.systemd.Unit.StartTransient (not implemented yet). The io.systemd.Unit.StartTransient call should accept only the ‘context’ portion of the output, without requiring any runtime data such as state (e.g. pid) or statistics.