Linux

Ok, so I have a very unique background in systemd. I worked at Red Hat supporting it basically as the primary support and I've worked with the developers of systemd at Red Hat directly. I no longer work there.

So first off, it's "systemd" all lower case. I don't care, but for some reason Lennart Pottering (creator) does.

systemd was a MASSIVE change. And Red Hat did a TERRIBLE job relaying it. To the point where I'm still trying to get my company to understand that it can NOT be treated like the old init systems. You can NOT just drop an init script in place and walk away and hope it works. Because a LOT of times it doesn't. Due to forks, switch users, etc.

systemd is NOT an init system. RHEL 5 and older had sysvinit as it's init systemd. RHEL 6 had UpStart as it's init system and looked exactly like sysvinit that no one even noticed. systemd again is NOT an init system. Init system is 1 part of systemd. systemd does a lot of cool things. It bundles applications together, it manages those applications and can restart them or kill children, it can do resource constraints, it separates out users from the system, and lots more.

Because it is not an init system there is a LOT LOT LOT of bad recommendations out on the internet where someone has X problem and person suggests Y and IT WORKS! ... except it doesn't REALLY work as far as systemd is concerned and you'll hit other issues or your application takes longer to start or stop and people just blame systemd.

It is systemd's fault that it has done an ATROCIOUS job of helping people adapt. It's a great example of RTFM. systemd's man pages are INCREDIBLE and extensive, but when you drop so much knowledge it becomes more difficult to find what you want/need. systemd.index and systemd.directives are your best bet.

So systemd does a lot of amazing things that sysvinit never attempted to do. It's never attempted to explain anything it expects everyone just learn magically. it's INCREDIBLY complex, but once you understand it's basics you can more easily get an application running, but as soon as there's a problem it'll just break your brain.

To give you an example, sshd's old init script is like 250 lines of bash. systemd's unit file comparative is like 12. Because systemd handles a LOT of what you manually had to handle before. BUT to get to that 12 you literally have to learn EVERYTHING new.

There is no "is it good or bad" here really imo. It's a completely different fundamental design. Red Hat made it for themselves. Other distros picked it up. It can be argued that lots of folks followed Debian and Debian had a few Red Hat board members that were pushing it. Whether they pushed it of their own accord or because they were with Red Hat I don't have a clue.

What I can say is at my current company they're suffering from a LOT of systemd issues and they don't even realize it. I've been working with Red Hat to try to get Insights to alert people to the failures and we're making progress.

To see if you have issues just to start run the two following commands:

# systemctl list-units --failed
# systemd-cgls

If you have any units that are failed, investigate those. If you don't need them, disable them. As for the systemd-cgls this shows HOW systemd is grouping things. ANY application that runs as a service (or daemon or application or runs in the background or however you wanna say it) should be under system.slice. ONLY humans logging into the system (meat bags NOT applications switching to users) should be in user.slice. A LOT of times what happens is an old init script is dropped in place, they start it, it has a switch user and systemd assumes it's a user and puts it into user.slice. systemd does NOT treat anything in user.slice the same as in system.slice and this WILL eventually cause problems.

So again, is it good or bad? Eh. It does a lot of cool things, but they did a MASSIVE disservice to ALL of us by just expecting to relearn absolutely EVERYTHING.