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Systemd by Example

496 points by Foxboron 5y ago

Anthony-G 5y ago
I just tried the first exercise of creating a default target and this web application is a great learning resource for Systemd. It should be noted that it works best as a complement to the author’s series on Systemd by example¹. I also love how the web application works without requiring multiple JavaScript dependencies hosted on third-party servers. ¹ https://seb.jambor.dev/posts/systemd-by-example-part-1-minimization/ https://seb.jambor.dev/posts/systemd-by-example-part-1-minim...
- zibzab 5y ago
  I was just wondering why everything loaded so fast and was so fluid...
pc86 5y ago
Site appears to be down
- BrightOne 5y ago
  HN hug!
ghoshbishakh 5y ago
Wow wonderful set of articles. A big thanks! Wanted to understand this stuff for a long time but could not give enough time to navigate the dense documentation.
steeleduncan 5y ago
Out of curiosity, how is this implemented? Is there a javascript VM running in the browser, a remote VM or can systemd be run in a container?
- zamadatix 5y ago
  There is a link to a post at the top which gives a detailed overview https://seb.jambor.dev/posts/systemd-by-example-the-playground/ https://seb.jambor.dev/posts/systemd-by-example-the-playgrou... but the short of it is it creates a limited remote container and pipes the CLI back and forth.
  - steeleduncan 5y ago
    Thanks!
setheron 5y ago
Wow. This is amazing. This is the bar needed for many learning resources. Thank you.
egberts1 5y ago
peterangular 5y ago
This is outstanding... I really wish I would have had this learning systemd as it would have saved me _hours_. Let's be real - a lot of Linux fundamental stuff is still pretty terse. Learning tools like this really smooth it out and optimize how long it takes to wrap your head around a concept. Also, I am a _huge_ advocate for hands-on in regards to retention. Adding to my favorites and will be passing this on over the years - thank you for such a great resource.
- native_samples 5y ago
  If anything the biggest problem the systemd docs have is verbosity. It's all classic UNIX man pages, a billion pages of detail on every possible setting with no useful examples anywhere. Fortunately the core system is simple enough that the learning curve isn't too steep but I'd really hate to try and learn it from the official docs. They don't even apply CSS to the HTML versions of the docs.
  - westurner 5y ago
    Wikipedia: https://en.wikipedia.org/wiki/Systemd https://en.wikipedia.org/wiki/Systemd Web: https://systemd.io/ https://systemd.io/ Src: https://github.com/systemd/systemd https://github.com/systemd/systemd Systemd manpage index: https://www.freedesktop.org/software/systemd/man/ https://www.freedesktop.org/software/systemd/man/ https://www.freedesktop.org/software/systemd/man/systemd.html# https://www.freedesktop.org/software/systemd/man/systemd.htm... : man 1 systemd man systemd man init ...: man systemctl man journalctl man systemd.timer man systemd-resolved The Arch Linux wiki docs for systemd are succinct: https://wiki.archlinux.org/title/systemd https://wiki.archlinux.org/title/systemd Fedora docs > "Understanding and administering systemd" https://docs.fedoraproject.org/en-US/quick-docs/understanding-and-administering-systemd/ https://docs.fedoraproject.org/en-US/quick-docs/understandin... RHEL7 System Administrator’s Guide > "Chapter 10. Managing Services with SystemD" https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/system_administrators_guide/chap-managing_services_with_systemd https://access.redhat.com/documentation/en-us/red_hat_enterp...
    - 5y ago
mikepurvis 5y ago
Maybe slightly off topic, but I'd love to hear about people's experiences using systemd as process manager inside a container, specifically for the unprivileged container case, where systemd would be launched in user mode, so only doing process management, without all the other kernel-hook stuff going on. I really like systemd, and I really don't like supervisor. So I'd love to figure out how to make this work. I know the easiest thing would be to ignore the user mode business and just use podman, where the work has already been done [1], but at least in the short term that doesn't help for more restricted environments like cloud kubernetes. [1]: https://www.redhat.com/sysadmin/improved-systemd-podman https://www.redhat.com/sysadmin/improved-systemd-podman
- mrweasel 5y ago
  May I ask why you'd want to use a process manager inside a container? I just consider Docker my process manager. If my application crashed, Docker will deal with it.
  - mikepurvis 5y ago
    A valid question— certainly there's a school of thought that says one process per container, end of story. However, there are lots of applications out there (especially legacy ones, think stuff like Zoneminder) which are made up of multiple small daemon-type processes sharing state across ports and maybe even the filesystem, and have a strong reliance on system services like cron or log rotation. Yes, with effort an application like this could be be fully "ported" to a container-native setup, but the path of least resistance is often to just make the container environment present as being more like a full VM.
    - eternityforest 5y ago
      I get the impression a lot of the entire point of containers in those things is to deal with those awful zoneminder style designs, PHP junk that needs specific Apache configs, etc. I prefer to just avoid any application that requires a service to in any way be configured to account for the app. It's bad enough that Zigbee2MQTT is a separate process, but it's acceptable because it is a pure layering model and as long as you are local only and not needing passwords, there's no manual config. Things like ZM that need an actual database are just insane. Multi-page configuration instructions for something that the(Sadly closed source) AgentDVR does with one process, no containers, no major configuration to conflict with anything else. But modular apps exist, so we need containers to make them act like monoliths.
synergy20 5y ago
I like all those 'learnXbyexample' sites, though I really hope I can have a drop down menu or side-bar to access the TOC instead of going back to homepage each time for next subject.
rmetzler 5y ago
Just the other day I noted on Twitter how bad the official systemd website is for users. I'm looking forward to this site recovering from HN hug.
mkaic 5y ago
I just learned the absolute basics of systemd the other day while trying to set up an auto-restarting game server on an RPi for my little sibling, and finding helpful examples was extremely difficult. This seems like a perfect solution!
cies 5y ago
Since systemd I never had to learn about my init system, it basically just works. For to reasons. 1. On desktop the old init systems were quite good already, before systemd was introduced. Systemd made it better, as I've been told: I never had any beef with it (oh boy did I have beef with init systems in the old days, not only on desktop...), I did not do any benchmarks to see that it shaved off a few seconds in startup time (and helps remove lots of fragile network mgmt code). 2. On server I now use Docker. It has no init system. And when I need one I use one that fits the docker world (i.e. supervisor).
- mdaniel 5y ago
  > It has no init system. Apologies that I can't link directly to the "--init" flag but docker actually does have an init, it's just (err, was?) compiled into the binary: https://docs.docker.com/engine/reference/commandline/run/#options https://docs.docker.com/engine/reference/commandline/run/#op... My recollection is that it either adopted, or inspired, https://github.com/Yelp/dumb-init#readme https://github.com/Yelp/dumb-init#readme which folks used to put into their Dockerfile as the init system back in the day Folks (ahem, I'm looking at you, eks-anywhere[0]) who bundle systemd into a docker container are gravely misguided, and the ones which do so for the ability to launch sshd alongside the actual container's main process are truly, truly lost 0: https://github.com/aws/eks-anywhere/issues/838#issuecomment-995409842 https://github.com/aws/eks-anywhere/issues/838#issuecomment-...
- tpetry 5y ago
  I recently switched to multirun [1] which in my case is superior to supervisor. I don't have to create any config files anymore, and it behaves exactly as i want it to: If one on the processes dies the complete container will die and docker's restart-policy takes place. [1] https://github.com/nicolas-van/multirun https://github.com/nicolas-van/multirun
  - cies 5y ago
    ...and no need to keep a python interpreter in memory :) Good tip, I would like something that that's offered by my $distro.
throwawaymanbot 5y ago
FunnyLookinHat 5y ago
I will up-vote every single one of these "_______ by example" sites that are made. I'd also love to see a "Buy a Coffee" or quick 5-10 USD donation button on each one - and if you want a commissioning for one throw a patreon or kickstarter up and I'll share it around. I found the gobyexample site to be invaluable when I first encountered the language, and now I send people there BEFORE I send them to the official go docs (which is saying something - because the official docs are great!). Here's hoping we can get well-structured documentation that scaffolds like these to replace most medium posts in the top results of most Google searches! :-)
taf2 5y ago
I was very anti systemd initially but mostly because it meant the many initd scripts I had for different services would no longer be usable or the daemons I had would no longer need to self mange their own pid files. But mostly it was out of fear - knowing how many battle scars each of those shell scripts had learned or forking lines of code had adapted could be lost… fear that maybe systemd would not carry those lessons forward… I let go and it has been pleasantly easier and much less stressing then I imagined… more examples like this are great thanks!
rob_c 5y ago
The missing documentation. Just hope they manage to keep it up to date. The feature creep here is immense despite the claims it's modular because individual executables do fixed tasks... Don't get me wrong I understand the power of systems but it's not written with a OG UNIX mindset in mind which is a little sad.

496 points by Foxboron 5y ago

I just tried the first exercise of creating a default target and this web application is a great learning resource for Systemd. It should be noted that it works best as a complement to the author’s series on Systemd by example¹. I also love how the web application works without requiring multiple JavaScript dependencies hosted on third-party servers. ¹ https://seb.jambor.dev/posts/systemd-by-example-part-1-minimization/ https://seb.jambor.dev/posts/systemd-by-example-part-1-minim...

zibzab 5y ago
I was just wondering why everything loaded so fast and was so fluid...

pc86 5y ago

Site appears to be down

BrightOne 5y ago
HN hug!

ghoshbishakh 5y ago

Wow wonderful set of articles. A big thanks! Wanted to understand this stuff for a long time but could not give enough time to navigate the dense documentation.

steeleduncan 5y ago

Out of curiosity, how is this implemented? Is there a javascript VM running in the browser, a remote VM or can systemd be run in a container?

zamadatix 5y ago
There is a link to a post at the top which gives a detailed overview https://seb.jambor.dev/posts/systemd-by-example-the-playground/ https://seb.jambor.dev/posts/systemd-by-example-the-playgrou... but the short of it is it creates a limited remote container and pipes the CLI back and forth.
- steeleduncan 5y ago
  Thanks!

setheron 5y ago

Wow. This is amazing. This is the bar needed for many learning resources. Thank you.

egberts1 5y ago

peterangular 5y ago

This is outstanding... I really wish I would have had this learning systemd as it would have saved me _hours_. Let's be real - a lot of Linux fundamental stuff is still pretty terse. Learning tools like this really smooth it out and optimize how long it takes to wrap your head around a concept. Also, I am a _huge_ advocate for hands-on in regards to retention. Adding to my favorites and will be passing this on over the years - thank you for such a great resource.

native_samples 5y ago
If anything the biggest problem the systemd docs have is verbosity. It's all classic UNIX man pages, a billion pages of detail on every possible setting with no useful examples anywhere. Fortunately the core system is simple enough that the learning curve isn't too steep but I'd really hate to try and learn it from the official docs. They don't even apply CSS to the HTML versions of the docs.
- westurner 5y ago
  Wikipedia: https://en.wikipedia.org/wiki/Systemd https://en.wikipedia.org/wiki/Systemd Web: https://systemd.io/ https://systemd.io/ Src: https://github.com/systemd/systemd https://github.com/systemd/systemd Systemd manpage index: https://www.freedesktop.org/software/systemd/man/ https://www.freedesktop.org/software/systemd/man/ https://www.freedesktop.org/software/systemd/man/systemd.html# https://www.freedesktop.org/software/systemd/man/systemd.htm... : man 1 systemd man systemd man init ...: man systemctl man journalctl man systemd.timer man systemd-resolved The Arch Linux wiki docs for systemd are succinct: https://wiki.archlinux.org/title/systemd https://wiki.archlinux.org/title/systemd Fedora docs > "Understanding and administering systemd" https://docs.fedoraproject.org/en-US/quick-docs/understanding-and-administering-systemd/ https://docs.fedoraproject.org/en-US/quick-docs/understandin... RHEL7 System Administrator’s Guide > "Chapter 10. Managing Services with SystemD" https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/system_administrators_guide/chap-managing_services_with_systemd https://access.redhat.com/documentation/en-us/red_hat_enterp...
  - 5y ago

mikepurvis 5y ago

Maybe slightly off topic, but I'd love to hear about people's experiences using systemd as process manager inside a container, specifically for the unprivileged container case, where systemd would be launched in user mode, so only doing process management, without all the other kernel-hook stuff going on. I really like systemd, and I really don't like supervisor. So I'd love to figure out how to make this work. I know the easiest thing would be to ignore the user mode business and just use podman, where the work has already been done [1], but at least in the short term that doesn't help for more restricted environments like cloud kubernetes. [1]: https://www.redhat.com/sysadmin/improved-systemd-podman https://www.redhat.com/sysadmin/improved-systemd-podman

mrweasel 5y ago
May I ask why you'd want to use a process manager inside a container? I just consider Docker my process manager. If my application crashed, Docker will deal with it.
- mikepurvis 5y ago
  A valid question— certainly there's a school of thought that says one process per container, end of story. However, there are lots of applications out there (especially legacy ones, think stuff like Zoneminder) which are made up of multiple small daemon-type processes sharing state across ports and maybe even the filesystem, and have a strong reliance on system services like cron or log rotation. Yes, with effort an application like this could be be fully "ported" to a container-native setup, but the path of least resistance is often to just make the container environment present as being more like a full VM.
  - eternityforest 5y ago
    I get the impression a lot of the entire point of containers in those things is to deal with those awful zoneminder style designs, PHP junk that needs specific Apache configs, etc. I prefer to just avoid any application that requires a service to in any way be configured to account for the app. It's bad enough that Zigbee2MQTT is a separate process, but it's acceptable because it is a pure layering model and as long as you are local only and not needing passwords, there's no manual config. Things like ZM that need an actual database are just insane. Multi-page configuration instructions for something that the(Sadly closed source) AgentDVR does with one process, no containers, no major configuration to conflict with anything else. But modular apps exist, so we need containers to make them act like monoliths.

synergy20 5y ago

I like all those 'learnXbyexample' sites, though I really hope I can have a drop down menu or side-bar to access the TOC instead of going back to homepage each time for next subject.

rmetzler 5y ago

Just the other day I noted on Twitter how bad the official systemd website is for users. I'm looking forward to this site recovering from HN hug.

mkaic 5y ago

I just learned the absolute basics of systemd the other day while trying to set up an auto-restarting game server on an RPi for my little sibling, and finding helpful examples was extremely difficult. This seems like a perfect solution!

cies 5y ago

Since systemd I never had to learn about my init system, it basically just works. For to reasons. 1. On desktop the old init systems were quite good already, before systemd was introduced. Systemd made it better, as I've been told: I never had any beef with it (oh boy did I have beef with init systems in the old days, not only on desktop...), I did not do any benchmarks to see that it shaved off a few seconds in startup time (and helps remove lots of fragile network mgmt code). 2. On server I now use Docker. It has no init system. And when I need one I use one that fits the docker world (i.e. supervisor).

mdaniel 5y ago
> It has no init system. Apologies that I can't link directly to the "--init" flag but docker actually does have an init, it's just (err, was?) compiled into the binary: https://docs.docker.com/engine/reference/commandline/run/#options https://docs.docker.com/engine/reference/commandline/run/#op... My recollection is that it either adopted, or inspired, https://github.com/Yelp/dumb-init#readme https://github.com/Yelp/dumb-init#readme which folks used to put into their Dockerfile as the init system back in the day Folks (ahem, I'm looking at you, eks-anywhere[0]) who bundle systemd into a docker container are gravely misguided, and the ones which do so for the ability to launch sshd alongside the actual container's main process are truly, truly lost 0: https://github.com/aws/eks-anywhere/issues/838#issuecomment-995409842 https://github.com/aws/eks-anywhere/issues/838#issuecomment-...
tpetry 5y ago
I recently switched to multirun [1] which in my case is superior to supervisor. I don't have to create any config files anymore, and it behaves exactly as i want it to: If one on the processes dies the complete container will die and docker's restart-policy takes place. [1] https://github.com/nicolas-van/multirun https://github.com/nicolas-van/multirun
- cies 5y ago
  ...and no need to keep a python interpreter in memory :) Good tip, I would like something that that's offered by my $distro.

throwawaymanbot 5y ago

FunnyLookinHat 5y ago

I will up-vote every single one of these "_______ by example" sites that are made. I'd also love to see a "Buy a Coffee" or quick 5-10 USD donation button on each one - and if you want a commissioning for one throw a patreon or kickstarter up and I'll share it around. I found the gobyexample site to be invaluable when I first encountered the language, and now I send people there BEFORE I send them to the official go docs (which is saying something - because the official docs are great!). Here's hoping we can get well-structured documentation that scaffolds like these to replace most medium posts in the top results of most Google searches! :-)

taf2 5y ago

I was very anti systemd initially but mostly because it meant the many initd scripts I had for different services would no longer be usable or the daemons I had would no longer need to self mange their own pid files. But mostly it was out of fear - knowing how many battle scars each of those shell scripts had learned or forking lines of code had adapted could be lost… fear that maybe systemd would not carry those lessons forward… I let go and it has been pleasantly easier and much less stressing then I imagined… more examples like this are great thanks!

rob_c 5y ago

The missing documentation. Just hope they manage to keep it up to date. The feature creep here is immense despite the claims it's modular because individual executables do fixed tasks... Don't get me wrong I understand the power of systems but it's not written with a OG UNIX mindset in mind which is a little sad.