How to Crash Systemd in One Command
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However, linux is missing basic functionality other os's offer, and systemd is showing up and trying to fill in those blanks. This is open source, if you don't like systemd, if you think it's crap, if you think there are obviously better ways to do it, well, what are you waiting for then?
Systemd is winning because they showed up and basically nobody else did. It's open source fork it and 'do it right'. Or point out the problems and hope that someone else will step up instead?
I think the world would better place if people spent less time griping and more time fighting to get their patch that fixes the problems merged. I guess coding is harder than writing blog posts though.
EDIT: I'm not saying systemd is perfect or even good. My point is that the people writing the code are going to have the final say, whether it's right or wrong, and it is unlikely that people writing blog posts lampooning it are really going to make a difference. I mean systemd has been despised and highly criticized from the beginning, and look where we are.
As the other comments have stated, there have been several systemd drop in attempts, such as this one:
http://uselessd.darknedgy.net/
But maintaining them is terribly difficult when Redhat is pouring money into people to work on it full-time. There are lots of systemd-free forks, including ones for Debian and Arch. But you need a large user base to continue to use these forks so other people will be encouraged to support them. Money, donations and good ole kudos help too.
TL;DR we don't live in the open source world you think we do.
Canonical tried to compete with Upstart but failed.
What's curious is why Debian fell. It was the cornerstone.
I'm curious what functionality other OSes had that Linux did not before systemd came along. It seems to me that it has been subsuming functions of other systems on Linux that were already present, as opposed to offering anything new.
Socket activation? inetd/xinetd. Timed start of programs? Cron and At Logging? rsyslog/syslog-ng/etc. DNS? -- dnsmasq, powerdns, bind, etc.
Honestly, I think if system had stopped at doing init, and focused solely on that and doing the best damned possible job of it, there'd be less hate. I think what's pissing off a lot of the systemd haters is the scope creep of the project has undergone. I was personally fine with the idea of systemd when all it was promising was init and service management. But then oh, were going to take over /dev, and cron and logging, and logins and DNS and (to be determined). Ahh, thanks, but no thanks.
Uniform daemon/service handling. Just look at the scripts in /etc/init.d (or wherever they are located in your particular SysV init setup). It's a total mess.
The rest of what systemd offers I can't comment on because I'm not familiar with it. But it is clear to me that systemd's declarative .service files are a billion times better than shell scripts.
#!/bin/sh
#
# $OpenBSD: apmd,v 1.1 2011/07/06 18:55:36 robert Exp $
daemon="/usr/sbin/apmd"
. /etc/rc.d/rc.subr
rc_reload=NO
rc_cmd $1
However, imho, shell scripts are great for that kind of work. Services come in all sort of shapes, some are proper daemons (fork, cd /, close([stdin, stdout, stderr]) and the rest), some are a little worse to say the least. And more often than not, the later is your super business critical important app built in house by incompetent developers.
The point being that services comes in all forms and shapes, and having a scripting language for integrating them and, if needed, compensating for crappy software is extremely useful.
Another aspect is that programs contain bugs, and the more complex a program is, the more bugs it contains. Keeping PID 1 as simple as possible should be a goal, nobody needs an http server inside its init system (or a dhcp client, or a dns resolver or...).
For some years now, the Gentoo Project has OpenRC/runscript (specialized shell for init scripts). It works really really well and it's quite simple to write an init script in it. It's a bit sad that it wasn't more considered in other distributions.
"proper daemons" are broken by design. Perhaps your "incompetent developers" know something that you don't?
https://cr.yp.to/daemontools/faq/create.html
How can I supervise a daemon that puts itself into the background? When I run inetd, my shell script exits immediately, so supervise keeps trying to restart it.
Answer: The best answer is to fix the daemon. Having every daemon put itself into the background is bad software design.
What I think is that we see an extreme case of "Not Invented Here". To be honest, OpenRC (at times) was displayed as Gentoo-Only-Project, despite being very portable.
I however want to highlight another general purpose Linux distribution that seems to be kicking along well (ie. not just being an anti-systemd distribution) and uses OpenRC.
Alpine Linux: https://alpinelinux.org/
I have seen it being used and worked with people who have been using it for a while. I never really got into it myself - lack of time being the reason.
On the other hand if the daemon is written by incompetent developers and is doing very stupid stuff then it is a good thing that it doesn't fit. The developers will have an incentive to fix their broken code. And even with systemd it is possible to run arbitrary shell scripts at startup (afaik) which could start the daemon so they aren't totally out of luck.
> For some years now, the Gentoo Project has OpenRC/runscript (specialized shell for init scripts).
But is a scripting language really needed for daemon management? If the answer is no, then a more limited configuration language (systemd's .service files) is better.
Limiting startup scripts wouldn't protect against much anyway, because it would only defer problems into the daemon you are starting up.
> Uniform daemon/service handling.
As others have pointed out, Linux did not lack this, and there were quite a number of systems that provided such on Linux.
What is not uniform about the previous service handling implementation in debian?
What? Should I have to know everything about systemd to comment on one specific part of it? I don't know about alternative init systems either, all I wrote is that for service management: systemd >> SysV.
> What is not uniform about the previous service handling implementation in debian?
I can't tell you since I don't use Debian. I can tell you that in Ubuntu there are lots of inconsistencies. Like different service scripts respond differently to the help command.
Even the "status" commands output varies between scripts.
This means there is no way to introspect a service to know if it supports things like the "restart" command or if "stop" and then "start" should be used instead. This also means that making a robust GUI tool for handling services becomes hard/impossible.
Why are you framing the conversation as if these were the only options?
> I don't know about alternative init systems either
Oh, so you are speaking from ignorance. I suggest learning about the alternatives such as OpenRC and the management tools such as daemontools, runit, and s6.
There are many solutions to these problems, although they may not be supported (by default?) in your favorite distro. Judging the Linux ecosystem by the failings of one distro isn't helpful.
I hold no animus towards the systemd project's goals or aspirations, but I have yet to hear a compelling reason for systemd to be shipping in it's current state.
I am, in a way, reminded reminded of PulseAudio. I kept PA of my desktop and laptop for years, having heard about PA being a complex nightmare to configure and make work that caused audio to break. Eventually, there was an application I needed to use that had a hard dependency on PA, so I bit the bullet and installed it. And everything magically Just Worked. My only complaint at the moment is that the pactl command seems more fiddly and verbose than it might need to be.
A closer look at the complaints about PA showed that many of them were older. This gives me the impression that PA was in fact a steaming pile that broke audio at one point, but eventually matured into something functional and useful.
And I think this is where systemd is at present: perhaps a good idea, but its implementation is not yet production ready, and should not be the default on production systems. And the project's continued scope creep is working against it in that regard.
systemd wasn't reliable or fit for purpose for servers when it got shoehorned in to everything.
When it comes to production servers you need stable and reliable. Not new and shiny. You're ideally rarely having anything happen on the server other than "run this software"
There is the classical "box in the corner sending and receiving data over the network".
And then there is the new "bunch of software in a container in the cloud somewhere".
And with the latter definition, stable and reliable seems to be of lesser importance in the eyes of the faithful. This because they can just fire off a new instance of the container if the existing one falls over (Uptime by machinegun as i like to think of it).
http://www.commitstrip.com/en/2015/07/08/true-story-fixing-a...
On either case, respawning time and scalability are limited by data coherence needs.
Frankly i think it would have gone nowhere if Canonical didn't decide they needed to copy Windows' "one volume slider pr program" thingy that was introduced in Windows 7 or there about.
Note btw that these days Poettering is no longer involved with PA development.
BTW, the main goal of systemd seems to be to create a single baseline for desktop Linux in code rather than spec.
It is a "continuation" of the -kit mentality that spawned within Freedesktop (or frankly within Fedora, at it seems said distro is basically the Petrie dish for anything under the Freedesktop umbrella).
With only a single master volume control I'm often fiddling with it to keep things at a reasonable level. With per program volume, I'm fiddling with levels less often and spending more time just listening.
When I plug in any new audio device, whatever I'm playing/recording automatically sinks to the most recent device. Seamlessly. So if I'm on mail.google.com and a GVoice call comes in, I can take the call, and during the call, plug in my USB headset.
It just works.
Mac can't do that. Windows can't do that. Linux/PulseAudio can. And that kicks ass.
I do it almost daily when I come home and plug in my Bose Companion 5 into my Macbook (USB Speakers)
It could also have been a borked install as well. But I'm sitting in front of a Win10 install on a Surface 4 Pro, and it can't auto-sink audio.
In fact, I quite often start music playing on the laptop (chrome/Google Play Music) and then power up my bluetooth headset -- it initially uses eSCO when it routes the audio over (mono) and then switches to A2DP a few seconds later
Maybe the issue is something to do with the SW (chrome/firefox?) you use for GVoice? Or maybe there are some edge cases that I'm not triggering (in particular, a USB headset is effectively a new soundcard and not just an audio sink; I can completely believe windows is flaky with them especially with third party drivers)
You are talking about a headset welded to a soundcard, that you then insert into a data bus each time you want to use it.
It completely fucked up the audio on my desktop at the time. Lots of cracking and hissing, some really weird delays as well.
With 16.04, PA has decided to not recognize the analog ports (headphone, microphone) on my motherboard. They are still there, and I can use ALSA programs to control the volume and play audio. But they just disappear after a couple seconds. It is annoying enough I might just move back to Ubuntu 14.04.
Could you please elaborate on what some of those are?
> systemd is showing up and trying to fill in those blanks
I haven't really kept on top of all systemd releases, but all I can see is them replacing things that already exist, just doing them in a different way.
I agree the init system replacement was necessary, but I'm struggling to understand why and how it extended to trying to extinguish and replace every core function of the operating system ecosystem.
That's rubbing a lot of people the wrong way, especially as mentioned in the article, those who adhere to the unix philosophy of do one thing and do it right.
I get the strong impression that systemd is driven by ego first, and technical innovation second.
But writing blogposts and making non-coders aware of some of the frustrations and dangers system administrators face will help the "business people" understand, and hopefully can put pressure from another angle.
We'll never all agree on one way of doing things, but I think that it's valid to socially encourage coders who have such a large sphere of influence and whose code can potentially be very harmful, to take more care and consider things outside their immediate bubble.
That blogpost alone has driven a lot of good discussions in this very thread, and I think that's as good and as healthy as helping more directly with submitting code.
All production ready Linux distros (RedHat (and by extension CentOS), SuSE and Debian) are all running systemd and as a systems administrator for a large company I _must_ adopt it, I don't have a choice.
I run devops though for a small business and we've avoided the issue entirely using runit for our software.
For every person whinging online about systemd, there are hundreds of people using it every day in their laptops and servers without giving it a second thought.
Systemd is "winning" because Red Hat are throwing money at it as a way to control the ecosystem.
http://cr.yp.to/daemontools.html http://smarden.org/runit/
The more you look at any of DJB's software, the more of the future you'll see.
Systemd doesn't observe the Unix philosophy and that bothers many people.
What bothers me is that systemd doesn't do that, and that somehow this "unix philosophy" criticism seems to be an excuse/defense for crappy design and code.
And the userspace tools don't follow this either. Quoting http://prog21.dadgum.com/139.html :
> The UNIX ls utility seemed like a good idea at the time. It's the poster child for the UNIX way: a small tool that does exactly one thing well. Here that thing is to display a list of filenames. But deciding exactly what filenames to display and in what format led to the addition of over 35 command-line switches. Now the man page for the BSD version of ls bears the shame of this footnote: "To maintain backward compatibility, the relationships between the many options are quite complex."
Why, for instance, does ls have its own sorting options if the sort command exists? If ls, the most quintessential UNIX command, can't do one thing and do it well, why should anything else?
Crashing an init process is a very bad thing, is it not? Wouldn't less surface area be a better approach?
* https://news.ycombinator.com/item?id=8904429
* http://unix.stackexchange.com/a/197472/5132
It is true that the userspace helper programs of some init system suites, such as sysvinit's telinit, work by sending signals to pid 1. But 1) they send signals to pid 1 because pid 1 is the service manager, not because it's the system manager, and 2) they could do something else other than sending signals (like sending D-Bus messages). The choice to use signals is a design decision of the init system suite, and not a part of the inherent requirements of being pid 1.
It is also true that with prctl(PR_SET_CHILD_SUBREAPER) you can move reaping away from pid 1. But at that point, the proper function of pid 1 is nothing, except perhaps to respawn pid 2 if it wants to. And as I argued in the other comment in this thread https://news.ycombinator.com/item?id=12600734, that's silly and you should just make the kernel do it.
I don't see any explanation in any of those links, or the things they link to, about why pid 1 is receiving signals. You claim twice that SIGINT, SIGPWR, and SIGWINCH are things that pid 1 can receive, but I have no idea why it might receive them. Can you explain?
You are exemplifying the people with off-the-top-of-the-head designs for init that I mentioned. The signals to process #1 from the kernel are rarely included, or even thought of, in such designs; despite the fact that they are the things that a process #1 program cannot escape and the child reaping is actually the least of its work and the thing that it can mostly escape. Here you are with yet another off-the-top-of-the-head design being thrashed out in a discussion forum, and you have not even encountered this stuff to know that a design has to include it, as evidenced by the questions about TTYs and windows.
As I said, go and look at many actual process #1 programs, such as Gerrit Pape's runit, Felix von Leitner's minit, and the system-manager program from the nosh package. They all have to handle these signals, and they all do. Don't repeat ... ahem! ... some other people's mistake of not learning about existing softwares and mechanisms.
The nosh system-manager and systemd both discuss them in their manual pages. They both have an explicit list of signals and what they trigger. The manual for /etc/inittab in van Smoorenburg init also discusses these signals and what they are, as do the manual for Joachim Nilsson's finit (http://troglobit.com/finit.html) and its TODO list.
I recommend some manual reading. (-:
SIGWINCH for a keyboard request is a thing that I did not know about, yes. But this is opt-in functionality for any process that has any VT open and is suitably privileged, and it is simply traditional for init to call ioctl(0, KDSIGACCEPT, SIGWINCH). Any process can request this, not just init; any signal can be used, not just SIGWINCH. And by default, no signal gets sent, neither to init nor to any other process. So init does not need to handle it.
(This of course leaves aside the question of whether anyone uses this functionality. How many users who are not init system developers know about this? And how many people have machines with physical keyboards that are not just running some window system that puts the keyboard in raw mode, anyway?)
See https://github.com/torvalds/linux/blob/v4.7/drivers/tty/vt/k... and L593-602 (initialized to 0 and disabled by default), https://github.com/torvalds/linux/blob/v4.7/drivers/tty/vt/v... (KDSIGACCEPT ioctl allows any suitably privileged process to request this), and http://www.fifi.org/doc/console-tools-dev/examples/spawn_log... (a separate daemon for doing this - via SIGHUP, incidentally - which says, "Note: this functionality has become part of init", implying it was originally not part of init!).
SIGINT on Ctrl-Alt-Del (if reboot(LINUX_REBOOT_CMD_CAD_OFF) has been called), and SIGPWR on power failure from the two drivers that implement it, are sent via the kill_cad_pid() function. This does default to pid 1, but that's just a default. And it's very easy to change that setting in userspace; it's a sysctl, /proc/sys/kernel/cad_pid.
See https://github.com/torvalds/linux/blob/v4.7/init/main.c#L998, which defaults cad_pid to init, and https://github.com/torvalds/linux/blob/v4.7/kernel/sysctl.c#..., the sysctl implementation.
The two drivers that implement SIGPWR, incidentally, are the S390 NMI handler and the SGI SN Platform's system controller driver, both of which I'm pretty sure see no use today. It's usually sent by a userspace process these days, which again could just choose to not use signals.
So none of the signals you've mentioned are pid 1's responsibility, They are traditionally pid 1's responsibility, yes. But those are two very different things, especially if we're talking about using PR_SET_CHILD_SUBREAPER to move all the interesting work out of pid 1.
The remainder of the signals handled by sysvinit, finit, runit, and nosh are all generated by userspace, and minit handles no other signals. And not all of these init systems bother to call KDSIGACCEPT.
I recommend being less condescending, especially if you're going to be wrong. (-:
powershell solves this by using structured data everywhere at the expensive of not working that well with plain text.
You should be able to run something like
ls -l | sort +date,-size
There are plenty of ways to do things better with basic text interfaces - a more standardized header format for example.
If most tools just output tabbed separated values with a header, or the same thing vertically.. ie..
foo bar baz
1 2 3
4 5 6
foo 1 4
bar 2 5
baz 3 6
Or at least more tools like 'ifdata' that is part of moreutils.
$ ifdata -pa wlan0
192.168.1.2
Bryan Cantrill even said in a presentation something like that it should be "Write programs to handle json text streams, because that is a universal interface" these days.
> ls -tl | sort -k 5 -n
ls -l | sort +date,-size
You'd end up with something like
ls -l --full-time |sort -k 6,5rn
We could have had a sort that let you do '+date,-size', instead we have a 'universal interface'.
I can't see how you would qualify this statement, which is utterly false. Specifically, systemd adoption was the result of political pressure by LP (the author), who works at Red Hat. There are plenty of other choices out there. The idea that systemd won because of some kind of meritocracy is wrong. It was mostly political with some technical discussion at the edges. Most people "making the decision" actually just outsourced their critical thinking to the Debian Technical Committee. That's how we ended up with most distros adopting systemd. Systemd is better than sysvinit (for some values of "better"), and that is what the Debian TC voted on, and what caused them to adopt systemd. Not that systemd is better than other, more modern init systems.
Upstart was almost good, but its really frustrating to use. OpenRC is decent, but confusing.
systemd solved problems, not only that it solved them well.
The scope creep of systemd is something that is a bit alarming, however even with the creep it's doing a good job. The tools that it is building work fairly well, and its a relatively new project.
The scope creep is really bad. It's not just bad, it's terrible. I don't want a program that's an init, and replaces xinitd and replaces my logging system and replaces cron. That's all totally beyond unnecessary.
Even with full process management, I'd hardly say it is the best. I have had cases where I stopped a service on a systemd box and it did leave child processes running. It's command line tools are terrible.
In fact it's this creep that keeps people from even being able to make drop in replacements. uselessd was a fork that kept up for a bit, but lost maintainership. With systemd being RedHat funded for full time development, it's very difficult for independent programmers to put in the time to make anything that can get adopted in the way it is.
Before, I could simply do "sudo service xxx start". Now, with systemctl, everything is much more cumbersome. Just run "systemctl list-units". Ho boy, you get a huge list of... things. Not just what used to be called services or daemons, but units belonging to mount points, /dev entries, and who knows what.
Granted, it is probably easier to create service scripts for developers than with init.rc or upstart (although I never had a problem the few times I had to muck with them). But as a simple consumer, I do not feel systemd solves any problem I had. It just made things some things that worked fine before slightly more confusing, and there are some regressions every now and then while other programs are getting ported to systemd.
* Binary log files (WHYYYYY; OTOH you could argue that the only proper place to do logging is to a remote database.)
* Monolithic nature - everything gets shoved in to the daemon, making it harder and more unusual to do things without it.
* Servers - systemd seems to be focused on a desktop lifecycle, where users interactively log in, have settings and log out. It is less clear how secure or well this inter-operates with services running as 'users' for privilege separation. I think this may have recently gotten better.
It stores everything in binary logs, however your old system didn't store it at all. You had a daemon (syslog, rsyslog, etc) that wrote them as plain text. If you start those daemons, you at exactly the same spot as before. Just with an additional copy in a binary log. Which btw, journalctl can do some magical things, and you should take some time to play with it.
systemd is not monolithic, or at the very least its a distributed monolith. The vast majority of services happen in their own userspace process.
Systemd excels with servers, since it standardizes how their execution gets defined. It takes only an added line to spawn them in their own namespaces, set cgroup restrictions, prevent network access, etc. Before hand, doing these things was very hard, so no one did them.
Systemd is a Jenga tower. Yes, there are lots of little pieces, and yes, removing a few won't hurt anything, but it's still fragile, and rather inconsistent. "Parts" like the journal, are a separate executable, but are not managed like other services. It uses a poorly documented ipc interface to talk to the various parts, and the configuration files are a nasty tangle of symlinks and control files stretching across the filesystem. It's just not a very well engineered piece of software.
But honestly, even an extra 30s booting a server is nothing, I don't give a shit about boot times on my servers.. I care about what order my services are started in- my servers should be 100% reproducable otherwise you could have bugs that never get found except in 1% of cases.
And since it's turtles all the way down 1% of one system can be a lot of problems in a 2,000,000 server architecture.
So "Fast boot" in the way systemd achieves it is not beneficial for me.
It was not.
http://0pointer.de/blog/projects/the-biggest-myths.html
Myth: systemd is about speed.
The first points that it details regarding the thesis of systemd is that it is a good init system, and a good init system is fast, and that SysV init is not fast.
The first time it begins talking about things a service management system should be interested in is about half-way through with "Keeping Track of Processes".
It spends roughly the rest of the document on important service management things, but to dismiss the idea that "systemd is about speed" is a myth is too much.
systemd IS about speed of booting -- during the development there were flame graphs showing how doing all this in parallel you could make the system boot really really fast. A lot of time was spent making the boot process with systemd minimal, or speedy.
Personally I'd prefer a less speedy service management system that didn't open listening sockets for my daemons so that it could deal with starting services out-of-order... to make the boot occur in a more parallel fashion... to make the boot faster.
EL6 and its derivatives was upstart, debian and its derivatives was upstart. The vast majority of linux systems were upstart for a long period of time. Other systems did not switch to upstart, because it introduced headache.
Switching init systems requires quite a bit of work. The fact that they all switched to systemd shows that beyond political pressure, they needed a better system.
At no point was it necessary for systemd to actually be better than upstart at being an init system. It just had to be bigger by the time it got to Debian.
We exercise our power to decide in cases of overlapping jurisdiction (6.1.2) by asserting that the default init system for Linux architectures in jessie should be
D systemd
U upstart
O openrc
V sysvinit (no change)
F requires further discussion
[...]
Therefore, the resolution reads:
We exercise our power to decide in cases of overlapping jurisdiction
(6.1.2) by asserting that the default init system for Linux
architectures in jessie should be systemd.Oh, wait, we weren't. But although I don't miss the rickety init scripts, I've grown more and more worried about stuff like this, enough to ponder replacements (in Go or Python, which seem to be generally acceptable for systems software these days).
Ignoring for the moment the usual biases against Python, how feasible/how much support would it be/have to build something to replace systemd (by having PID 1 do the minimum possible, in C, and having the rest done with Python)?
There are still a lot of issues I've had with Docker, which I won't go into. It also can't replace everything running on your Linux system. But it's a neat idea and big players use it in production for huge workloads.
Now the whole AWS-containers, docker-machine, swarm, mesos, coreos, kubernetes thing is a cluster fuck of choices .. but you have choices. And unlike running an Ansible script on some provides base image (which is totally different from Rackspace, Linode, etc.), you are guaranteed your container will work on any docker engine with little modification (your orchestration files may change though).
I have a feeling, for better or worse, containers will be the future and will stick around long after systemd hopefully dies.
There is already a great deal of bad blood between the two because of the reworked cgroups management.
And there is also the likes of CoreOS that is basically systemd-the-distro.
Never mind that we have the likes of xdg-app/flatpak that is basically aiming for what you are thinking about, and it is systemd dependent.
All bugs are terribly easy to spot in hindsight. I don't think it's fair to criticize this one in that fashion. Systemd has lots of pros and cons, but the age of this bug isn't interesting IMO. Its severity is, but that only speaks to the critical need to patch it ASAP.
Systemd has replaced a lot of init systems in the linux ecosystem and the general development practices of the project is leaving a huge footprint of code that might be exploited.
If they aren't involved, I'm sure they probably know a few different exploits for the system already.
https://igurublog.wordpress.com/2014/02/17/biography-of-a-cy...
Of course, it would also be simple for the kernel to allow PID 1 to die/crash, and just restart it instead of panicking. I don't know why the kernel continues to treat PID 1 so specially—if the ewontfix.com PID 1 is sufficient, it's simpler for the kernel not to bother with the reparenting logic and stop treating PID 1 as a special process.
By design all processes inherit from PID 1 (directly or indirectly), so you always have an unbroken tree from every process back to PID 1. PID1 aka init is supposed to do bookkeeping (e.g. zombie processing), and if PID1 crashes the bookkeeping records are lost.
Because of this, it is better to fail hard, instead of allowing for corrupted process trees or similar.
Also, ps, top and basically every program that works with processes expects one root process for the tree. Breaking this would basically break compatibility with every existing userland (which the kernel cares the most about!)
By "Breaking this" you mean "fixing the fact that pid 1 can't crash and restart"?
> Because of this, it is better to fail hard
It can't be fixed because it would "break compatibility" where that "compatibility" is that the machine should panic?
You're not really making a good case for why this can't be changed.
Why not
* pid 1 exits
* kernel re-executes init as a new pid 1
* userspace continues on as if nothing happened.1. Processes that are reparented to init aren't actually considered children of init for the purposes of the wait() system call. Their ppid still becomes 1, so parent process walks work, but when they exit, the kernel immediately cleans them up.
Zombies still exist in this change, as long as their parent still exists; the only thing that changes is that processes (zombies or not) are not reparented to init when their parent dies. Direct children of pid 1 are not treated specially.
2. When init is about to exit or crash, the kernel turns it into a zombie. It then starts a new init process and reparents the old init to the new one, allowing it to do things depending on the cause of the crash. Direct children of the old init have lost their parent, and are treated like any other parentless process as described above.
3. If execing the new init fails, the kernel panics.
This would be completely backwards-compatible. (I might even argue against 3, to remove all worry about init crashing; since pid 1 is no longer required to do anything, if exec fails, the kernel can just leave pid 1 as a stuck process table entry, let the system continue running, and log something to dmesg so the sysadmin can diagnose the problem and reboot the machine cleanly.)
Kind of reminds me when the behavior of rm -rf / was changed in solaris.
I can't find the article, but basically someone pointed out that they couldn't change the behavior of rm -rf / because posix defined how it should work. Someone then pointed out that the spec says that trying to remove the parent directory(i think?) should fail, and since rm -rf / includes removing the parent directory, it was within the spec that it should fail.
> The bug is caused by an error check that filters out garbage sent to PID 1. The check works correctly, except that the resulting action is a too harsh: instead of complaining and dropping it will abort the process.
* https://www.reddit.com/r/linux/comments/54yfcd/how_to_crash_...
In fact, the opposite was the case. The root of the problem was identified in the GitHub bug report:
* https://github.com/systemd/systemd/issues/4234#issuecomment-...
* hhttps://github.com/systemd/systemd/commit/d875aa8ce10b458dc2...
What happened was that Lennart Poettering removed an error check that filtered out zero-length messages. This left the flow of control to fall through to a later point where an assertion, that had been earlier added by Lennart Poettering with the assumption that this check for zero was in place (as it had been at the time), then triggered.
Of course, no-one that I have seen has yet asked why "" as a command-line argument to systemd-notify results in a zero-length message in the first place. After all, according to the doco that would be length 1, a single terminating LF byte, not zero length. That said, the server still should be proof against zero-length network input.
https://www.reddit.com/r/linux/comments/54yfcd/how_to_crash_...
> So let's summarize this. There's a bug in some software. OMG! Shock! This of course never happened before!
> The bug is in not exploitable remotely. The bug does not allow privilege escalation nor insertion of code. This of course makes the bug a massive vulnerability like there was no other on the planet ... ever. As bad as heartbleed multiplied by the Debian OpenSSL random generator bug to the power of 10.
> The bug is caused by an error check that filters out garbage sent to PID 1. The check works correctly, except that the resulting action is a too harsh: instead of complaining and dropping it will abort the process. Such a bug is of course unprecedented and the authors of said software should be stoned and flogged right away given the severity of the issue: after all a safety check worked a bit too well, and we really can't have that because undefined behaviour of course would be a lot better than a local DoS.
> The project the error was found in is large. Yet the number of CVEs collect so far is pretty small comparing it witht other projects of similar extent. Given that another bug was discovered now this obviously shows how incompetent the programmers are and that security is a unknown concept to them.
> The program the bug was found in is longer than 50 lines of code but runs with privileges, all written in a low-level programming langauge that many call little more than a fancy macro assembler. The code runs on top of an operating system kernel written in the same language but running with a lot higher privileges and consisting of expoentially more lines of code including drivers of questionnable quality. This together is of course proof that the project at hand is flawed conceptually to its core.
> Dha!
> Lennart
> (More seriously: yes this is a bug, we should fix it. But it's very low impact and the bruhaha it generated appears wildly out of scale. If all bugs in the wider Open Source ecosystem would have a similarly low impact we'd live in a much much safer world!)
So while this is a bug, the author is overreacting just to make systemd look bad.
"If you think systemd doesn't need privilege separation because it only parses messages from local users, keep in mind that in the Internet era, local attacks tend to acquire remote vectors. Consider Shellshock, or the presentation at this year's systemd conference which is titled "Talking to systemd from a Web Browser.""
* Whether release builds should have assert() enabled.
* Whether a process #1 program should use assertions at all.
* Whether assert() is the right mechanism to use for input validation.
* How a process #1 program should recover from assertion failures.
EDIT: works fine with Windows, without installing Bonjour/iTunes.
The most succinct explanation of Systemd possible.
having read this post I'd say a slightly less succinct but infinitely more informative version would be
> "Systemd is defective by design because they totally disregard the fail-safe by design rules"
So either the kerbel devs did take over udev development...
BTW GKH was oddly absent in that thread, and the kernel devs ire was aimed at Sievers...
But in a fight between GKH and T'so, I'll take T'so. /dev/random's ...interesting design aside, I frankly trust T'so far more than I trust GKH, who backs LP, a person I emphatically do not trust, in a lot of things.
Is it really that serious of a bug? You have to be a local user in order to execute it. Are other OS's somehow resilient to the actions of local user to degrade the OS?
>The Linux ecosystem has fallen behind other operating systems in writing secure and robust software. While Microsoft was hardening Windows and Apple was developing iOS, open source software became complacent.
He must be unaware of the numerous patches Microsoft and Apple issue on a regular basis to fix their "secure and robust software".
Containers may prove to be a sufficient sandbox, assuming this is not executable against kdbus (which is shared across containers since it's in the kernel).
while true; do NOTIFY_SOCKET=/run/systemd/notify systemd-notify ""; done
* http://jdebp.eu./FGA/unix-daemon-readiness-protocol-problems...
while true; do NOTIFY_SOCKET=/run/systemd/notify systemd-notify ""; done