I am a Linux user, but I don’t really know how most things work, even after years of casual use on my Main, I just started getting into Devuan and wondered then, what exacly does systemd do that most distros have it? What even is init freedom? And why should I care?
Systemd is the first program that runs once the kernel has started. It’s job is mostly just starting up other processes, and managing those other processes. If you don’t know what systemd is, then you probably shouldn’t care about if you’re using it or not, it’s good software but there are fine alternatives.
What makes systemd particularly interesting is that it is different from historical init systems. Historically these init systems were an unholy mess of shell scripts. This offers maximum flexibility, but limits the functionality of the init system itself. Systemd replaces these shell scripts with simple ini-like service files that allow everything to be declared simply and declaratively, and allows specifying more rich metadata, like dependencies. But it’s different, and some people place a higher value on “how it’s always been” than pragmatism. I personally have zero sympathy for them because throwing out objective progress to hold onto a broken system designed for 1960s computing is just dumb.
I had to battle with the fucking initd and upstard before systemd. Those stupid headers of the scripts in /etc/init.d/ we wonderfully undocumented, didn't have syntax checks, depended on a bunch of other shell scripts that didn't have any damn comments in them.
systemd was going to happen sooner or later because nobody was going to put up with that bullshit forever.
Those people arguing about "do one thing right" blablabla don't care about principles, they care about superiority. They want to feel like they're the minority who can do stuff so that in forums they can be toxic and respond with "RTFM" or "LMGTFY". They don't want it easier and more functional, they want it hard so that they can gatekeep.
Like a bunch of Catholics: I experienced pain, so you have to too!
systemd can containerize services! To do that kind of stuff with initd, you'd have to know how create process-, user-, and network namespaces, and a bunch of other stuff.
It’s especially funny because systemd isn’t one program any more than GNU is. It’s a project. systemd-initd handles init. systemd-journald handles journal logs. systemd-resolved handles DNS resolution. Etc. Each systemd daemon has one area of responsibility!
I never used openRC (outside of Docker containers that run Alpine) so I wouldn’t know. Linux community has enough controversies, init utils shouldn’t be one of them
I was with you until the last paragraph. Just about every init system is different from historical init systems. Do you really think OpenRC or runit or any of the other init systems people are using have any similarity to SysV init? I think you’re attacking a strawman in the last paragraph. (Edit: Except Slackware users. Slackware still does init the way it’s traditionally been done, but I can’t think of anyone else who does)
I mean to a certain degree, I can understand if people find a problem with Poetterings approach of doing things !CORRECTLY!. Like, systemd-resolved resolving A-records with multiple addresses ina deterministic fashion because it’s not defined not to be deterministic, and because actual load balancing would be better. It’s not wrong, but it’s breaking everything. And it got patched after some uproar. And there are a few things like that.
But at the same time - I don’t think people appreciate how hard doing process management right on linux can be, especially if the daemon to run is shitty. Like, init scripts just triggering the shutdown port on a tomcat - except the tomcat is stuck and not reacting to the normal shutdown port and now you have a zombie process and an init script in a fucked up state. Or, just killing the main process and for some reason not really removing the children, now there’s zombies all over the place. Or, not trying appropriate shutdown procedures first and just killing things, “because it’s easier” - except my day just got harder with a corrupt dataset. Or, just trying soft and “Pwease wexit Mr Pwocess” signals and then just giving up. Or having “start” just crash because there was a stale PID from an OOM killed process around. Man I’m getting anxiety just thinking about this.
And that’s just talking about ExecStart and ExecStop, pretty much, which I have done somewhat correct in a few init scripts back in the day (over months of iteration of edge cases). Now start thinking about the security features systemd-analyze can tell you about, like namespaces, unmapping syscalls, masking parts of the filesystem, … imagine doing that with the jankyness of the average init.d script. At that point I’d start thinking about rebooting systems instead of trying to restart services, honestly.
And similarly, I’m growing fond of things like systemd-networkd, systemd-timesyncd. I’ve had to try to manage NetworkManager automatically and jeez… Or just directly handling networking with network-scripts. Always a pleasure. Chucking a bunch of pretty readable ini-files into /etc/systemd/networkd is a blessing. They are even readable even to people rather faint on the networking heart.
Linux is based on unix, which was an operating system designed to run on computers like the PDP-11 of the 1970s.
The problem is that computers have changed a lot, and Richie and Thompson couldn’t perfectly forecast all those changes. Most notably, it predates the internet.
All your chat is about technical issues, and both sides allways talk about the technical pros and cons of each system.
But i remember reading when debian team changed to systemd the arguments included these: 1- now Linux works like Windows and we do not like it. 2- now all depends on the systemd team, while init gives more freedom, so started devuan. 3- init and systemd can do the same but…here all the technical blah blah. By the way, if devuan exists and works well… 4- last and not least, systemd lets lock out the system (distro).
I am not an IT guy, just an user…so an ignorant. My questions: are those statements still valid or wrong? Even today the number 4 gets mi confused, it is, or was, a real reason?
Sorry my wording, my first language is not English.
Easier compared to what? Easier compared to sysvinit, of course. Easier compared to all the other alternatives? Six of one, half a dozen of the other, on balance, I would say.
But SystemD has inertia behind it now. If you run into problems, there are probably 1e10 web pages out there that will help you fix it. That’s why Debian solidified on SystemD: not because it’s any better than any of the others, but because it’s the same as everybody else.
Why should you care? Tech diversity is good, and people can try out different approaches. Aside from that, there’s not a reason. Systemd is a really good desktop init.
What is init freedom? It means the init system can be changed without other software breaking because there is a dependency on some functionality of the init. In this case, a dependency on systemd. Although it’s probably a dependency on a subproject under the systemd umbrella rather then systemd itself.
Why systemd? It’s tailored to weirdnesses in the Linux kernel. The Linux kernel isn’t perfect, and it’s user land isn’t tied to the kernel. Systemd is a shim which papers over the oddities. I don’t remember which oddities, but they’re there and people ignore them.
Were there dumb decisions made? Yes, especially for the server side. I should test out some other inits for servers, but it ultimately works fine.
When you boot up your Linux, it will mount the root file system and start one program. That program is systemd. Everything else on your system will be started through systemd or processes that systemd started.
That’s why it is important, everything else on your system is build on top of it. That’s also why it is difficult to replace, if you use something other than systemd, you need a completely new set of config files for that other thing or your software might not work properly. Most distributions have given up on that, as it’s just more work for a niche audience, and they just require systemd instead.
As a regular user you don’t really have to care all that much, most stuff systemd does will happen automatically in the background and be setup by your distribution. It can still help to get familiar with systemd tools like journalctl as that’s where all your error messages go and systemctl is how you start, stop or disable services on your system. If you use something other than systemd those tools won’t exist and something else will take their place.
As for why people don’t like systemd, it follows the kitchen-sink approach to software and does a lot of things at once. It replaced a whole zoo of smaller utilities like inetd, syslog, cron, atd, … Some people dislike this loss of modularity, while most the rest are happy that they have one tool that does all of those things well, especially since systemd can do a lot of those tasks better and in a more unified way than previously.
As for why people don’t like systemd, it follows the kitchen-sink approach to software and does a lot of things at once.
For people new to Linux I just want to point out - for better or for worse this goes against the Unix philosophy.
Write programs that do one thing and do it well. Write programs to work together. Write programs to handle text streams, because that is a universal interface.
One thing that people miss - either out of ignorance, or because it goes against the narrative - is that systemd is modular.
One part handles init and services (and related things like mounts and sockets, because it makes sense to do that), one handles user sessions (logind), one handles logging (journald), one handles networking (networkd) etc etc.
You don’t have to use networkd, or their efi bootloader, or their kernel install tool, or the other hostname/name resolution/userdb/tmpfiles etc etc tools.
wow thank you for taking the time and explaining that! I didn’t except to learn that today right before bed today or ever. It’s these kind of great comments that i come to lemmy for. Just know that i really appreciate it!
It mostly causes heated discussions and a feeling of nostalgia for simpler times.
When your computer finishes loading the kernel, you have to tell it what to do next. There are dozens of systems and services that have to run (once or keep running) for everything to work. Mounting your disk partitions, bringing the networking up, starting the GUI, initializing all kinds of services, etc.
Once upon a time most (all?) distros used sysVinit, adapted from Unix’s System V to do that. It was simple and very easy to understand and setup: Very basically the init program would call scripts by alphanumerical order (passing “start” to scripts starting with S and “stop” to ones starting with K). You’d place these scripts in /etc/rcX.d, X being a number, the runlevel (and you had just a handful of runlevels, like halt, reboot, single user, gui, etc). Want to run something between starting the network and bringing up sshd? Just create a script in /etc/init.d and link it to /etc/rcX.d naming it SNNmyscript, with NN being a number between the ones in SNNnetwork and SNNsshd. Want to disable a service? Change its script name from S… to K… Change startup sequences? Just change the NN.
Beautiful. But although it worked perfectly for most of us, it did have deficiencies. An obvious one is that it ran these scripts sequentially. Even if your computer was using 0.1% of its power to run each of them, you’d be waiting for each one to run in a single queue.
So a very nice and polite guy came up with systemd. Instead of simple scripts running sequentially, you could now create “unit files”, describing each “thing to do”, for what “targets” (similar to runlevels) that thing is needed, which scripts to run to make that thing happen, and which previous things should have been done before this thing (dependencies). With this, your computer can fire up multiple startup scripts (and stopping scripts) at the same time, only making sure to queue stuff so dependencies are met. For example, you don’t need to wait for sshd to start your database server, but you do need networking before you mount shared disks.
That made boot times much better, but at the cost of complexity and maintainability (and here come heated discussions…).
The problem is that not everyone wanted that tradeoff, but systemd was shoved down everyone’s throat as most (all?) distros adopted it.
So init freedom is a reaction to that, offering you the option of multiple init systems (there are more than just sysVinit and systemd).
No offense to all the other init systems, but I’d stick with sysV if you’re really after simplicity and backwards compatibility with most older systems (and the old ways), or systemd, because it became the de facto standard, it’s faster and more modern.
Should you care? If you have to ask this, then no.
If you had to craft your own init scripts and configurations, and had a ton of legacy scripts, or maybe were building very simple barebones systems, or very complex, always changing startup scenarios and targets or runlevels, or want to exercise your “freedom” just for the heck of it, then you could care.
If you’re a distro hopper (i.e. are more dedicated to “use Linux” than to use applications which run on Linux), having tried 5 different init systems may be one more thing to brag about in distro hopper meetings.
If you’re getting into Linux to learn Linux administration for career purposes, systemd is what you’ll find in commercial systems.
If you’re after an OS to just be an OS (i.e. just run your programs), just pick a well supported (community) and mainstream one, it will most likely come with systemd, and you’ll probably never need to touch systemd. My wife (not technical) has been using exclusively Linux for 15+ years, and I can assure you with 100% certainty that she doesn’t know which init system is there, or what is systemd or sysV.
If you’re new to Linux, curious and want to learn all you can about it, I’d say there are many other interesting and useful things in Linux to learn and care about before you go down this rabbit hole, summoning some nice nostalgic but outdated tech from the dead.
It doesn’t do “only” that; I was comparing it with other init systems and described their main, basic init functionality. Sorry if I didn’t do it well.
Now, in my personal opinion, I do find it good in that these being under one umbrella project led to fairly good integration between these aspects of “system management” as a whole. But I do also concede that this may feel like too many responsibilities handled by one project
Pretty sure you mean systemd-networkd here. I find systemd-networkd to be very nice for headless systems, but NetworkManager seems to be a better fit for desktops because of the integrations it has available with KDE/Gnome/system tray
Once the kernel has loaded itself, it needs to start up userspace as well. This is usually (perhaps exclusively) done by starting an ‘init’ program as process number 1, which then starts up all the other userspace programs: systemd is no different in that regard. It solves a variety of problems that traditional inits have, though:
rather than having near-incomprehensible shell scripts to start, stop, etc. all your programmes and services, it uses INI-style service files which are merely fiddly. They’re kept in a few logical places, not ‘everywhere’
starting and stopping services is done with simple, consistent commands - systemctl enable tomcat will start the Tomcat webserver at next boot; start, restart, stop and disable do basically what you think. Shell scripts are… less predictable, especially between distros.
rather than having to inspect all of your scripts and work out what order they start in, SystemD just lets you declare what they depend on, and it works it out for you - much simpler, much more robust.
rather than needing a separate tool to manage scheduled events (usually a chron-like, like anachron), SystemD just lets you write a ‘timer’ with the same syntax as its service files. They can be set to only trigger based on other events, like start-up, so you can do once-an-hour database snapshots (but only if the DB is running) very easily. That’s painful with traditional inits.
also manages disk and network mounts, so you don’t need a separate tool for those, and you can trigger other events off of them as well. That was also painful in older inits.
and power events too, if you want to trigger other tasks before sleep or when your laptop wakes up. (Again, was painful before.)
log files all in one place and controlled in the same way and accessed with one tool - again, traditional inits aren’t like that.
(advanced usages) works well with cgroups, so if you’re looking to limit the CPU time on a web service and make sure that it only uses its share of memory, that’s dead easy. Very difficult with traditional init.
You can get a reasonable idea of what systemd is doing with a systemctl status at the command line; shows you the overall system status, with a nice tree view of what’s running and what caused it to start. Getting that kind of overview on a eg. SysV init is much less simple.
Administrators and devops generally love it; it’s very simple and straightforward and consistent and predictable. Certain devs dislike it, due to the original author, or feelings of overreach and complexity (although it’s much simpler than learning everything that it replaces), or because they’re attached to Bash scripts. (You can trigger Bash scripts with SystemD if you like, but they’re not ‘in control’.)
<span style="color:#323232;">DESCRIPTION
</span><span style="color:#323232;"> systemd is a system and service manager for Linux operating systems. When run as first process on boot
</span><span style="color:#323232;"> (as PID 1), it acts as init system that brings up and maintains userspace services. Separate instances
</span><span style="color:#323232;"> are started for logged-in users to start their services.
</span><span style="color:#323232;">
</span><span style="color:#323232;"> systemd is usually not invoked directly by the user, but is installed as the /sbin/init symlink and
</span><span style="color:#323232;"> started during early boot. The user manager instances are started automatically through the
</span><span style="color:#323232;"> user@.service(5) service.
</span><span style="color:#323232;">
</span><span style="color:#323232;"> For compatibility with SysV, if the binary is called as init and is not the first process on the
</span><span style="color:#323232;"> machine (PID is not 1), it will execute telinit and pass all command line arguments unmodified. That
</span><span style="color:#323232;"> means init and telinit are mostly equivalent when invoked from normal login sessions. See telinit(8)
</span><span style="color:#323232;"> for more information.
</span><span style="color:#323232;">
</span><span style="color:#323232;"> When run as a system instance, systemd interprets the configuration file system.conf and the files in
</span><span style="color:#323232;"> system.conf.d directories; when run as a user instance, systemd interprets the configuration file
</span><span style="color:#323232;"> user.conf and the files in user.conf.d directories. See systemd-system.conf(5) for more information.
</span>
After fighting with multiple network devices today, I feel like I have a right to be angry. Checking the info in dmesg what I see is that the system initially sets up all six NICs (two on the motherboard, four on a card) in the correct order with eth* names. Then something else comes along a couple seconds later (which I assume is systemd) and renames everything to enp* NIC names. If I move the card to a different slot or install a different card with the same model then all those enp* names change to something different, but dmesg still shows their initial eth* names in the expected order before being renamed.
“Predictable” names are anything but, and now you can’t even use the standard udev naming or even put link files under /etc/network/interfaces.d/ because all that stuff has been changed again so now I have to move all the link files to /etc/systemd/network/. I don’t know how anyone considers this a good thing when the convention keeps changing every few years and I actually have to do extra work to put the names back to what linux originally called them at each boot. Where does the madness end?
Yep I’m aware of it. Seemed like it worked for a bit, then reverted back to the enp* names. And then all the pages I was finding for manually renaming the devices said to put the files under interfaces.d for deb11 but oddly it only seemed to read those link files for a few reboots, then it would revert back to the enp names. Found something about using OriginalName because the name changes were overlapping, that worked for a few boots and then reverted back to the enp names. So then I found something about a Path statement using the full pci device names, and THAT worked for a few boots and then reverted. So now I found out that the link files have moved to the systemd/network folder so I’m waiting to see how long that lasts…
And I realize it sounds like I’m talking about a system I’ve been running for years… I actually just put together this machine last Thursday. I had to start with Debian 9 because I couldn’t get any newer memory stick images to boot (this machine doesn’t have EUFI support), upgraded to deb10 and everything was still working as expected with the grub lines to disable renaming. Upgraded to deb11 and it all went to hell. I’m having some serious thought of trashing the machine and switching to deuvian now even though I really want to support debian.
Uh… there’s absolutely nothing wrong with the hardware, it all works exactly as it should. It’s just systemd’s insistence on rearranging things that aren’t broken, and then changing how you fix the problems it created.
I have actually. I saw the post for their latest release earlier today and had been seriously considering switching over. This new machine is to replace my existing firewall as the old one has gone through several upgrades since Squeeze, so I’m trying to get something set up to rebuild everything from a clean installation and then I can simply swap out the hardware (and swap it back real quick if something doesn’t work right away).
No the changes for “net.ifnames=0 biosdevname=0” were still in there. Those worked fine for debian 8, 9, and 10 (with adjustments made in udev rules to rename eth4 and eth5 to wan0 and wan1), but neither option seemed to have any effect after upgrading to deb11. When I went searching for renaming the devices in deb11, the first several articles all stated to create link files in interfaces.d, but after all the trouble I went looking further and finally found one that referenced putting the link files in the systemd folder. I just linked the files so they are available in both locations, and that change has continued working for several further reboots so I’m crossing my fingers.
Oh god, does anyone still use NetworkManager by choice??? How would you even use it from the command line? I just configure the interfaces file by hand.
Systemd basically is what starts up other processes. You don’t need systemd, but you do need some init manager. Kernel loads, then calls up the init manager to load everything else. Anything you want to make run on startup gets added to the init manager.
Add comment