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Ask Slashdot: Can You Say Something Nice About Systemd?

Posted by samzenpus on from the use-your-words dept.

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:
  1. 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:
  2. 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.
  3. 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.
  4. Describe the Nice Thing in some detail. Don't assume, for example, that merely saying "Supports Linux cgroups" will be immediately persuasive.
  5. 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.

8 of 928 comments (clear)

  1. Nice Thing: systemctl status shows you log entries by db48x · · Score: 5, Informative

    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.

  2. Read of the better systemd commentaries around by Anonymous Coward · · Score: 5, Informative

    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

  3. Plays nicely inside a container by Rich0 · · Score: 5, Informative

    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.

  4. Stop means STOP by Rich0 · · Score: 5, Informative

    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.

  5. Hardening by icemaze · · Score: 5, Informative

    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

  6. Exit codes matter by Rich0 · · Score: 5, Informative

    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.

  7. Why dislike something you know nothing about? by backtick · · Score: 5, Informative

    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:/

  8. Journalctl logging is more secure (bug #1098132) by Anonymous Coward · · Score: 5, Informative

    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.