Slashdot Mirror
Ask Slashdot: Can You Say Something Nice About Systemd?
ewhac writes: "I'm probably going to deeply deeply regret this, but every time a story appears here mentioning systemd, a 700-comment thread of back-and-forth bickering breaks out which is about as informative as an old Bud Light commercial, and I don't really learn anything new about the subject. My gut reaction to systemd is (currently) a negative one, and it's very easy to find screeds decrying systemd on the net. However, said screeds haven't been enough to prevent its adoption by several distros, which leads me to suspect that maybe there's something worthwhile there that I haven't discovered yet. So I thought it might be instructive to turn the question around and ask the membership about what makes systemd good. However, before you stab at the "Post" button, there are some rules...
Bias Disclosure: I currently dislike systemd because — without diving very deeply into the documentation, mind — it looks and feels like a poorly-described, gigantic mess I know nothing about that seeks to replace other poorly-described, smaller messes which I know a little bit about. So you will be arguing in that environment."
Nice Things About systemd Rules:
Bias Disclosure: I currently dislike systemd because — without diving very deeply into the documentation, mind — it looks and feels like a poorly-described, gigantic mess I know nothing about that seeks to replace other poorly-described, smaller messes which I know a little bit about. So you will be arguing in that environment."
Nice Things About systemd Rules:
- Post each new Nice Thing as a new post, not as a reply to another post. This will let visitors skim the base level of comments for things that interest them, rather than have to dive through a fractally expanding tree of comments looking for things to support/oppose. It will also make it easier to follow the next rule:
- Avoid duplication; read the entire base-level of comments before adding a new Nice Thing. Someone may already have mentioned your Nice Thing. Add your support/opposition to that Nice Thing there, rather than as a new post.
- Only one concrete Nice Thing about systemd per base-level post. Keep the post focused on a single Nice Thing systemd does. If you know of multiple distinct things, write multiple distinct posts.
- Describe the Nice Thing in some detail. Don't assume, for example, that merely saying "Supports Linux cgroups" will be immediately persuasive.
- Describe how the Nice Thing is better than existing, less controversial solutions. systemd is allegedly better at some things than sysvinit or upstart or inetd. Why? Why is the Nice Thing possible in systemd, and impossible (or extremely difficult) with anything else? (In some cases, the Nice Thing will be a completely new thing that's never existed before; describe why it's good thing.)
We will assume out of the gate that systemd boots your system faster than ${SOMETHING_ELSE}, so no points for bringing that up. Bonus points are awarded for:
- Personal Experience. "I actually did this," counts for way more than, "The docs claim you can do this."
- Working Examples. Corollary to the above — if you did a Nice Thing with systemd, consider also posting the code/script/service file you wrote to accomplish it.
- Links to Supporting Documentation. If you leveraged a Nice Thing, furnish a link to the docs you used that describe the Nice Thing and its usage.
Betteridge's law of headlines is an adage that states: "Any headline which ends in a question mark can be answered by the word no.
Is this the right headline to apply it on?
I like that in the future when the integration is more complete, I'll be able to install a database or a webserver and then once in a full moon when a cosmic ray hits the process and kills it, systemd will just restart it.
Yes, you can do that with other tools too once you've learnt your lesson (many years ago I had 1.5 year uptime with Apache and then it suddenly crashed) and I am using one of those at the moment. What I like is that this will just work out of the box for newbies and veterans alike with no clunky configuration/interfacing.
If you have a service called 'foo', then 'systemctl status foo' not only shows you whether the service is running, it also shows you the last 10 log entries created by that service. This is great when the service failed; usually the error message will be right there.
How does it do this? Well, because all processes created by the service are in the same cgroup, all of the log messages (and even anything they print to stdout, which would have been lost otherwise) can easily be tagged with the service name (and a bunch of other metadata). You can use journalctl to query the journal for the logs from a specific service, and systemctl status does this for you.
The idea of booting services in parallel is nice, but the problem is that apparently it doesn't have a way to specify that you need to wait for a dependant service to hold off until the initialization of the dependancy is complete. Systemd considers it "booted" as soon as it launches, which causes people problems with unreliable network initializations and such that have been resolved for Sys-V style init scripts for years (if not decades.)
I do not fail; I succeed at finding out what does not work.
http://uselessd.darknedgy.net/ProSystemdAntiSystemd/
This comes from an "anti-systemd" source, but tries to cut through a lot of the controversy and hostility shown on both sides. Bear in mind, you only see the anti-systemd view on Slashdot, but you get just as much idiocy on the other side as well. For example, the Poettering "death threats" were actually a joke made by a bunch of people in an IRC channel. Here, read the log (ctrl-F "hitman"):
http://logs.nslu2-linux.org/livelogs/maemo/maemo.20130215.txt
I've been starting to migrate many of my services at home to containers to make them a bit easier to maintain (a bit of a tangent - having 5 containers instead of one host with 5 services means that you have to do 5x as many updates, but each update can at most break one thing at a time). This was trivial to do with systemd-nspawn.
With a command line that barely fills a terminal line I can launch a container, have it boot systemd inside the container, have a few bind mounts, and have it get its own IP like a lightweight VM. Within the container systemd just does whatever it is told to do, like launch ssh so that I can get in, configure the network, and launch whatever services the container was intended to provide. The container journal logs are symlinked back to the host log directory, so they're really easy to look at from the host.
Sure, you can do similar things with docker, but doing it with systemd involves less tooling in general.
Also, for simpler situations systemd-nspawn makes a VERY good substitute for chroot. In addition to doing everything chroot does, it starts a separate process namespace so you don't see outside processes from inside the container. It also automatically sets up /dev for you, sets up resolv.conf, etc - it can do all this while just spawning one program inside just like chroot does (so no need to run systemd inside). It can also set up bind mounts if you ask it to. When you exit it cleans up - no lingering bind mounts, or tmpfs, or /proc and such inside. Also, any mounts inside the container aren't visible outside, so you can run a backup on your chroot and not have it follow bind mounts, or try to save /proc/kcore or whatever. In fact, you could spawn 5 containers inside the same directory and they can have private /tmp and /dev and /proc while seeing changes each other make in the files in the actual chroot.
One thing I really like about systemd is that when you stop a service, it actually stops.
I used to run monit with openrc and when you wanted to restart a service you had to play games to ensure that it was really killed, and that the service state was cleaned up, and so on. Just telling openrc to stop the service just wasn't reliable at all - it worked well when nothing was wrong, but if nothing was wrong chances are monit wouldn't be doing anything.
Systemd is very effective at containing processes and their children and when you stop them, they are all gone for good. If you want to restart a service, systemctl restart service will get the job done 100% of the time, assuming the configuration/etc lets it restart. It does support graceful shutdown of individual services, followed by process genocide.
This also applies to things like cron jobs you launch through it. When the parent process ends, anything left gets cleaned up.
Systemd was forced down my throat by Arch Linux. I didn't know anything about the controversy back then, so I just thought: "There's probably a good reason for this, let's get to work".
I read some docs and I liked the security features a lot! You can tighten services easily with a declarative syntax.
Here's a snippet from my ntpdate.service file. You don't need much systemd knowledge to guess at what each line does:
PrivateTmp=true
ReadOnlyDirectories=/
InaccessibleDirectories=/boot
InaccessibleDirectories=/root
InaccessibleDirectories=/etc/ssh
LimitNPROC=1
DeviceAllow=/dev/null rw
DeviceAllow=/dev/urandom r
User=nobody
Group=nobody
CapabilityBoundingSet=CAP_SYS_TIME
NoNewPrivileges=true
I ended up enjoying that work and tightened things so much that I hit a bug, which was resolved in just a few days: https://bugs.freedesktop.org/s...
But I still don't know how to configure the network properly T_T
A small thing I've come to appreciate with systemd is that it actually cares about exit codes. This applies to any unit, including timer units (the equivalent of cron jobs). I ported most of my cron scripts over to systemd and suddenly started noticing scripts which had been having non-zero exits for ages, but fcron just didn't care about exit codes.
You can tell systemd to ignore exit codes for a process, or specific exit codes. However, I've found that in general using systemd I have a lot more awareness of abnormalities in my services.
Sure, you can often get away with ignoring exit codes, just as you can often get away with ignoring compiler warnings. However, in getting rid of them I fixed a few problems ranging from trivial to important, and my system is more robust for it.
I've killed systemd shutdowns hard after 15 minutes of timing out waiting for an nfs share that went offline.
The old system didn't do that. Not to detract from the lovely startup times, but it's not "all baked" yet.
My God, it's Full of Source!
OUTSIDE_IP=$(dig +short my.ip @outsideip.net)
Writing service files for my own daemons or modifying existing ones is pretty close to trivial. The files are short, easy to understand, and there isn't any risk of runaway child processes like there is with a sysvinit init script making them close to trivial to write and maintain. If anything I would say that's why so many distros are jumping on board.
I had to write service files as an early adopter, but it would also be useful for anyone rolling out their own daemons or that needed to tweak the behaviour of an existing service for their own needs. I imagine it would also lead to fewer packaging bugs.
Systemd is modular:
- It's broken up into multiple independent processes, each of which handles one major thing well.
- It's broken up into libraries so that commonly used code (such as parsing config files) is implemented once and shared among the services, saving memory (because you know how shared object libraries work, right?) and ensuring that there's only one implementation of any one thing that needs to be tested and debugged.
- Interdependence among services is minimized, although as with any real, complex system, there are chains of dependencies.
- Dependencies on and among services are handled on-demand so that only the services you need are running (often started well after boot). As a side effect, boot time is shortened.
- Process 1 (init) is very small, with minimal functionality, in order to minimize the chances that it will crash.
The above are all true, or at least they are consistent with claims made by the developers. Sure, I have negative things to say, which are also true, but I don't want to add to the noise of all the false negative claims floating around.
Background: I've professionally administered Unix and Linux machines for >25 years, including various BSDs, Linuxes, Irix, HP-UX, Solaris/SunOS, AIX, etc. I've been certified by several vendors or distributions, including, since 1999, Red Hat (which gives me quite a bit of background on their specific implementations over the years). I don't work for a company doing development of any OS or platform. heck, other than random 401K type aggregate ownership, I don't own stock in any company that cares about this issue at a deep level, to the best of my knowledge :)
Personal Bias about this thread: You pretty much lose all the credibility possible with me when you start of with "I ... dislike systemd because ... it looks ... like a poorly-described, gigantic mess I know nothing about ... ." (It's the "disliking something you know nothing about" that bugs me). Otherwise, I don't care much about this debate on a personal level. I currently admin boxes using systemd as well as everything else, and nothing about systemd has caused me anywhere near the heartache that it seems people who haven't used it much seem to feel about it.
Seriously, there're thousands of pages of documentation about what it is, how it works, and what most if not all of the design basis decisions are/were. I'll link you to a few of them because hey, you can get to slashdot and post, but you can't seem to use Google ;) (tongue in cheeck, of course). There're plenty of folks who DO have great detailed reasons on why they don't like bits and pieces of it, and you should be able to compare them to the various info I'm linking below.
Systemd has tons of upside and tons of downside. Most are pretty well detailed, although many of the gut reactions people seem to have to it are based on a lack of understanding about how it works and what it's compatible with, to wit "I can't use shell scripts for anything at startup anymore!" , "All of my old chkconfig or SysV scripts can't be included at all!", "It kills off syslog!", "The only reason it exists is to make laptops boot faster and in the server world we don't care", etc. Those are easily researched and the actual basis (or lack thereof) pretty easily found.
So, for why the systemd setup looks like it does, you can go back 4.5 years to where the announcement and rationale is described. Speed is part of it, as is device changability, as is double-forking, resource limits, and service state checking and recovery. Yes, it's a load of stuff. Definitely a system-wide approach VS a semi-random collection of various ways to do things all tacked together (which is, frankly, what most Unix and Unixlike systems are, through survival of the fittest).
http://0pointer.de/blog/projec...
http://0pointer.de/blog/projec...
http://0pointer.de/blog/projec...
http://0pointer.de/blog/projec...
http://0pointer.de/blog/projec...
Since RedHat's obviously the largest major proponent and arguably the source of the most production users, here's their documentation:
https://access.redhat.com/docu...
Here's the project page with loads of links about the software and uses cases:
http://www.freedesktop.org/wik...
And of course so many questions have been raised the developers have posted their rebuttals to myths or misunderstandings.
http:/
I have used Linux for 15 years without any problems.
Think again. For example, do you remember in the past 15 years you experiencing any of the following while using Linux?
- the desktop is tearing (vsync problem)
- suspend or hibernate is not working properly
- you get a blank screen when X.org starts
- making manual modifications to the system as a workaround for a bug
- a power management issue has bitten you, such as the system consuming too much power, overheating, or fan spinning constantly
I am not making comparison to Windows or Mac here, because they have their similar bag of problems. Your claim was about using Linux without any problems.
Caveat: I am a server admin.
With systemd, one can't even remotely log a journal natively, which is par for the course in many server environments. You can't make this stuff up, please see bug #1098132 (https://bugzilla.redhat.com/show_bug.cgi?id=1098132) At the time I'm writing this, that functionality still just *doesn't exist* in systemd/journalctl. It was almost pushed into the last revision, but the bugs were show-stoppers so was pulled. Even if it does go into the next systemd revision, how long until it's really kosher for solid/production environments? 1 year? Two? Three? Yet it's being pushed as the default *now*.
To explain why this is important: if someone cracks in, the log files are going to be one of the first things they muck with. You have locked down syslog/et al, so you can tell if they muck with the binaries, but the log files themselves are considered compromised. Logging remotely at the same time before the data even hits the disk creates another layer of safety, which you simply can't do with systemd/journalctl. One day you will, assuming you want the binary journal and journalctl, but even if you wanted those now you couldn't. Yes, you could rsync over a copy of the files, but there's a reason why people aren't just doing that for regular logs and this is going long.
Over the last decades, people have worked out tried-and-true systems for documenting and verifying logging. So from an audit perspective, with journalctl you can't lock down syslog-ng and that process, because you've introduced an untrustworthy one above it. They know the current strengths and limitations -- to the point that there are legal/liability issues involved for many if their logging goes wonky. Journalctl adds a layer between the systems they have that work (and even have protocols in place for in terms of auditing), and as of right now adds a *wonky* layer that's very buggy. And by buggy I mean prone to corruption and simply not doing as its told.
Here's the real kicker: most of this issue would go away if systemd was willing to allow the user to not use journalctl and let things like syslog-ng have that data in the raw. It is choosing not to allow that as a tactic, as opposed to what the users and tech itself wants, and so here we are.
Also, this entire proposition by samzenpus is inane. When one thinks backwards from what the motivations might be, none of them are good and make me lose that much more respect for the site.
systemd's logging system is a huge improvement over old legacy style text logs. It has more early boot logs since it can log while still in initramsfs, and with kdbus it will probably get even earlier and late logging; the goal is "metal-to-metal" logging.
Having structured and indexed logfile (called journal) is a huge improvement in many ways; it allows for rich meta-data like monotonic timestamps, high precision time stamps, UUID's, exe file names and paths, and incredible easy and powerful sorting and filtering with tools like "systemctl".
If you try to add meta-data like monotonic timestamps in flat text files, they become very long and cluttered, making them hard to read for humans.
Another problem with flat text files are the fact that watch scripts depends on the exact wording of the daemon output strings; if the developers changes the wording, third party scripts will fail. In a perverted sense, the exact wording have become a API that cannot easily be changed or extended.
Not so with systemd; it has a stable API and lots of language bindings. It is easy to make a watch script that targets the stable field's.
Some CLI examples: I have used full length options for readability and since systemd have excellent bash completion for everything, it doesn't involve much more typing.
journalctl --boot -1 --priority err
Show all log entries from previous boot only, that have log level "error".
journalctl --since -5m
Show log entries generated the last 5 minutes.
journalctl --follow --unit smartd.service
Follow (tail) the smartd daemons log output.
journalctl _KERNEL_SUBSYSTEM=usb --priority warning
Show only messages generated by the kernel USB subsystem that have log level "warning"
journalctl --field _PID
The "--field" option makes systemctl show all values of the following journal field. In this case it will show a list of all PID's that have ever written to the journal. Want to see every executable that have ever generated log output, substitute _PID with _EXE. Notice the underscore. Field values with underscores have kernel guarantee for being correct.
It is also easy to track two services that you suspect are causing each other problems:
journalctl --output short-monotonic --boot -u NetworkManager.service -u chronyd.service
This will show the log entries for NetworkManager and a sNTP client from the current boot, and show the output with monotonic timestamps. Nice.
It happens about 40 times a day on you average PC
No, it doesn't. I operate lots of machines with ECC RAM. I've seen ECC correction. Bits flip, but nowhere near that frequently. It's very rare.
Not to mention seamless upgrades between versions, and even mixing/matching packages from different archs for advanced setups. Freely up/downgrading stuff with DEB-based distros is a bliss. When I learned that RHEL historically didn't even support upgrades between major stable versions I was awestruck (they seem to have made improvements for this in 7, good for them...)