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[stapelberg]: Hi! So first of all, the type of this lecture

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is that it's going to be a workshop, just to make the expectations

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clear, I have a few slides prepared that

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should give you a general introduction

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and they will take

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probably about half of the time we have allocated

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for this slot, and afterwards

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we can answer your questions

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or have some hands-down hacking

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on actual packages.

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My name is Michael Stapelberg

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Just a quick show of hands so that I know my audience --

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who of you maintains a Debian package

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in Debian or derivatives?

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OK, that's almost everybody

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Perfect.

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How many of you actually added

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systemd support to their packages already?

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OK, a couple.

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Who of you are looking into doing that?

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OK, perfect! You are exactly the right audience.

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Great. So the topics I want to cover with my slides are:

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First of all, how systemd works for package maintainers
Great. So the topics I want to cover with my slides are:

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First of all, how systemd works for package maintainers

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That means I'm not going to cover all of it
First of all, how systemd works for package maintainers

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That means I'm not going to cover all of it

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And also it's not so much of a user standpoint

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but just what you need to know to get you started on testing your stuff in systemd.

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We will then have a look at an example service file

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where we'll make clear what all the different directives are supposed to mean

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We will look at the tmpfiles mechanism

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and at dh-systemd, a debhelper plugin

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We will consider a few more advanced examples, and then finally we will

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answer your questions, hopefully.

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So, non-topics for this presentation are:

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systemd sucks, let's just use something else instead

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When will debian ever finally switch the default, and essentially anything that ever came up on debian-devel. I'm not going to talk about that.

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This is just about how to make it work if you have already accepted that this is something that you want to do.

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So, how does systemd work?

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Essentially, where we previously had initscripts, we now have service files.

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Service files are just a special kind of unit files

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so the more generic term is unit files and that which corresponds to an initscript is a service file.

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So previously, you would have /etc/init.d/apache2 as an initscript

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and the corresponding file would be /lib/systemd/system/apache2.service

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Now what's important here to notice

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Is that the base name (apart from the .service suffix)

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needs to be the same, because what will happen is that

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systemd, when booting on a machine

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will look at all the services in /etc/init.d

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and use them if they are available

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but if there is also a service file, that will take precedence.

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So in order to make sure that systemd uses your service file and not

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your service file plus the old initscript, make sure that the name is correct.

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Before you ask, yes there are also mechanisms to make sure that

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when you have a name transition, because you've adopted the upstream name for a service file

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or something like that, then you can have a compatibility symlink.

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We can cover that later.

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And essentially, systemctl does what service did.

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So if you had service apache2 start

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Then you would use systemctl start apache2.service

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In recent versions, you can even skip the .service suffix so it would just be systemctl start apache2

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The systemctl tool is mostly for the actual users, or for you when testing.

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and just like you would usually use /etc/init.d/apache2 start as an actual user

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but "service" inside your maintenance script, we have something for that.

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Now, what we had in SystemV init were runlevels

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and they were poorly defined and different from distribution to distribution

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And what systemd does to replace them is that it has something called a target.

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A target is precisely the same as a runlevel

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it just has a much nicer name

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and the names are standardized between all the different distributions.

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The most important targets for you are basic.target, multi-user.target and graphical.target

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Each of them is more specific than the other

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in that it starts more services for a particular use case

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So basic.target is what everybody of you will run

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and then multi-user.target extends basic.target with more stuff

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and graphical.target brings in all the graphical components like a display manager

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and stuff that you would normally not use on servers where multi-user.target is what you would want to use.

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You can look that up if you care later on in the manpage systemd.special.

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Just as previously, with SystemV init

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we had symlinks to enable a service

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and these symlinks were created by update-rc.d

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we still have symlinks to enable a service

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now they're just created by systemctl enable

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Again, systemctl is what you would use as a user, or while testing, etc.

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And we have a maintainer script equivalent of that.

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Are there any questions so far? This is really the basic stuff.

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[question]: What is the reason there are different commands for the user and the maintainer scripts?

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[stapelberg]: I think will go into this later, but I can just briefly explain it

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The maintainer scripts also need to work on machines where systemd is not actually installed.
[stapelberg]: I think will go into this later, but I can just briefly explain it

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The maintainer scripts also need to work on machines where systemd is not actually installed.

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So that's why we can't use systemctl.

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Alright, let's look at an example service file.

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I just picked vnstat.service

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which is a tiny daemon that will just store (and plot later on) your network traffic.

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What you can see here is a very clear, human-readable configuration file

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And this is the service file. it's called vnstat.service.

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It starts with a [Unit] section, and you can see

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just like inifiles, which probably everybody of you is comfortable with

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or .desktop files, which have the same format, so this is actually a .desktop file.

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There are sections which are enclosed in square brackets, and then there's key/value pairs

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separated by an equals sign, so that's really simple.

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The first section is entirely just for humans.

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So the description will tell me what kind of service this is, if I'm looking at my system and wondering what is this that's starting up here.

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The second section is the [Service] section, and this is actually where

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all the relevant stuff is.

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What we specify here in the second line is ExecStart, which is

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the command that systemd will run when trying to start that service.

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In this case, it's really simple, you just start the vnstatd binary.

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What you need to notice here though is that systemd does not invoke a shell to start it up,

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so you need to specify the full path, and you don't have your usual

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shell stuff in your command line, so just keep that in mind.

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We also have the ExecReload line, and there could also be an ExecStop line.

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In the absence of an ExecStop line, systemd will just kill the service

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And it will do what many many people implemented in initscripts by hand

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which is to gently try to kill it, and if that doesn't work within a certain timespan

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then it will try to kill it harder, until it finally succeeds.

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The ExecReload line is pretty standard

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the thing is that not all of the services provide a way of reloading in the first place

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so we need to have such a line to tell systemd what to do on a reload command

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Some other service (you could probably think of the bind nameserver)

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have a different way of reloading (so you could call "rndc reload" in that case)

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but this one is really simple, it just sends SIGHUP to the service, and then it will reload.

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the $MAINPID is not actually a shell variable or anything

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it's just a special thing that you can use in unit files and service files in particular.

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And then we also have the User= line which will specify

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under which user this program will be started. That's pretty straightforward.

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The last section is also interesting

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it's called the [Install] section, and it has a line called

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WantedBy=multi-user.target

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And that essentially says that when this service file

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is enabled on the machine

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it will be pulled in by multi-user.target, so this specifies

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which runlevel it runs in, so to say.

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Are there any questions so far?

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yes -- microphone?

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[question]: can there be more than one WantedBy= line?

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[stapelberg]: Yes, there can be multiple WantedBy= lines.

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More questions -- over there?

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[question]: So just to make sure that I understand correctly

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If systemd tries to restart or reload a service

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it first executes this reload phrase, and then it execs

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the start phrase again?

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[stapelberg]: No, there's two different cases here. One is the reload case

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and the other one is the restart case.

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In the reload case, it just executes what's specified here

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If the service file supports reloading; if it doesn't, then you can't reload it.

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If you do a restart, it will

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first execute stop if present, or kill it if not present, and then start it again.

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[question]: Fine. OK, thank you.
first execute stop if present, or kill it if not present, and then start it again.

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[stapelberg]: one more question here?
[question]: Fine. OK, thank you.

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[stapelberg]: one more question here?

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[question]: Is there an equivalent to debian's force-reload,

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where you care so much about wanting it to reload that you're OK with it falling back to stop and start if necessary?

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which debian's sysvinit system does support in the usual skeleton file.

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[stapelberg]: I think there is a try-reload action, but I would have to confirm that. We can do that later.

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[question]: Is there also something to stop a service?

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[stapelberg]: Yes, I already mentioned that you can specify ExecStop=, and if you don't, it will just kill it.

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[question]: Sorry, I didn't hear that.

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[stapelberg]: one more question here?

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[question, quoting from a man page]: "tries to reload if possible and falls back to restart"

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[stapelberg]: He just said there's a "reload-or-restart" command in systemctl that does precisely what you asked for.

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[question]: Are there other things than start, reload, stop, and ... can you define other things?

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[stapelberg]: Can you clarify what you mean by that?

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[question]: For example, status, or I was thinking more about something specific to a certain daemon?

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For instance, fetchmail can have an "awaken" option

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it does a sleep of 5 minutes or something, and you can say "check right now"

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[stapelberg]: What exactly is the question? I still don't get it.

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[question]: Can you have some exec line in there --

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[stapelberg]: -- Oh, can we have a custom action, like in initscripts, is that what you mean? No, we can't.

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There are different ways of coping with that:

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Most often there's an alternative to what you want to do

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But I think it's really clean and nice that they standardized on a few verbs, and all of these work with all of the services

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(except for the reload one, obviously)

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but you can't have really custom weird stuff.

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You could ship that in an additional shell script. That's what I would usually use as a first suggestion

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if there's no specific, no better way of solving the problem. But we can discuss that later on.

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for specific services that you might have in mind.

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Any more general questions up until here?

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[question]: Maybe you answered and I missed it, but about the possibility of querying the status of the service?

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[stapelberg]: Yes, obviously. As I said, I will show that in the second part.

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Now, tmpfiles:

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The tmpfiles mechanism is really useful not only within systemd

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but also oftentimes when people read about it they think "hey, this could be useful standalone."

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What it does, is it provides a mechanism to configure creating temporary directories, like runtime directories.

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As a really simple example, I have here the lighttpd configuration file

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where we will essentially say "create a directory called /run/lighttpd"

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with this mode, this user, this group, and no more arguments.

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There are some arguments you could specify there, for cleaning it up every ten days or some delay like that

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that's all supported. This mechanism is much more powerful than this very simple example.

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it can also support not only directories, but also files, pipes, symlinks, etc.

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I don't want to go into all of the details, but this is the preferred mechanism to create a /run/something

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and it's much much cleaner than having all these varying mkdir commands

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that sometimes specify a user and a group and sometimes they don't and then they don't have a mode, etc. etc.

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So this is what we want to use. Question?

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[question]: There's no implicit conflict with other things, so I have to take care to do a proper namespace organization?

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and, for example, call my temporary directory like my service and not

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choose an arbitrary name which would perhaps clash with another service?

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[stapelberg]: Sure. I mean obviously you need to watch out for filesystem clashes in debian packages.

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That's just as it always has been.

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[question]: So it's the mechanism, you have to provide the policy.

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[stapelberg]: Yes, obviously.

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Alright -- service file location:

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oftentimes, the upstream provider ships a service file, and that's the way it's meant to be.

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because the upstream should know best how to install the service on a particular machine

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Now, that doesn't always happen

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but if it happens please use the upstream service file

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and if the upstream file is really broken, please work with upstream to fix it

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If it's broken in some minor detail, you might ask upstream

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if it's acceptable to change it in the way that it would be better

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I don't have any specific details; one example that would come to mind is that some

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upstream service files are actually pretty old -- like they were written in 2009 or something

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and by now they're, for example, referring to syslog.target as a dependency

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whereas syslog is autostarted nowadays by socket activation.

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So that could be removed, and then the service file would be simpler

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and more idiomatic, and that would be a typical change that you could push upstream

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I don't say that I expect any of you to know what the idiomatic service files

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are, and contribute that upstream; I'm just saying that it would be the right thing to do.

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Question?

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[question]: So you say just write the debian/packagename.service and .tmpfiles

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but most debhelpers also accept just debian/service and, just the type of the file

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without the package prefix if there's only one binary package -- is that supported?

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[stapelberg]: To be honest, I didn't test it, but i'm using the exact same debhelper plugin code

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that all the others are using, so I would expect it to be supported.

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What we also support, even though I didn't actually program it

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is "package.(and then some actual package name)" if it's only for a specific package in a set of all packages

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[ed: he means sourcepackgename.binarypackagename.service]
is "package.(and then some actual package name)" if it's only for a specific package in a set of all packages

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which is a typical debhelper feature in that sense.
[ed: he means sourcepackgename.binarypackagename.service]

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which is a typical debhelper feature in that sense.

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[question]: Thanks!

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[stapelberg]: Sure.
[question]: Thanks!

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[stapelberg]: Sure.

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Now, to actually cover that point, if upstream actually doesn't ship a service file and/or a tmpfile

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then you can just place them in debian/$yourpackagename.service and debian/$yourpackagename.tmpfile and it will be installed.

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It will be installed by dh_installinit, which might confuse you

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because dh_installinit is for initscripts and not for servicefiles

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and in fact, we by now have dh_systemd, so that's weird!

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The only reason why that is is because of historic reasons.
and in fact, we by now have dh_systemd, so that's weird!

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The only reason why that is is because of historic reasons.

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We first started implementing it in dh_installinit,

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but then it turned out that it would make the helper very complex and weird
We first started implementing it in dh_installinit,

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but then it turned out that it would make the helper very complex and weird

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and handling upstart and sysv and systemd all at the same time is really not a good idea
but then it turned out that it would make dhelper very complex and weird

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and handling upstart and sysv and systemd all at the same time is really not a good idea

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So we decided to leave it there for the time being, but eventually to migrate it

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If you use just the dh command it will all just work, you don't have to care

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In all the other cases, currently policy dictates that you still need to ship an initscript

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so that's all fine, and as soon as policy gets changed, I promise that we will be in a state where you don't have to care about this either.

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I already mentioned to please send service files upstream, but I'll just stress it again.

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Not only if you have an upstream service file and modify it and fix it, please send it upstream

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but also, if you create a service file, please send it upstream so that upstream can distribute it.

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Some upstream software might not agree; some are actually very thankful.

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Question over there

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[question]: Assuming upstream ships a valid service file, what's the best practice:

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Is it to call dh_installinit specifying the path in the upstream directory,

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or copying it into the debian directory before dh_installinit is invoked?
Is it to call dh_installinit specifying the path in the upstream directory,

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or copying it into the debian directory before dh_installinit is invoked?

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[stapelberg]: In case upstream installs it, just let upstream install it. I'm not sure I get the question.

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[question]: The question is: in case upstream does not install it; they ship it, but they do not install it?

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[stapelberg]: OK, in case they don't install it, and then what is the second part of your question? just put it in debian/ as I explained.

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[question]: So you can put it manually in debian/ before dh_installinit is invoked.

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Or you can invoke dh_installinit with the path from the upstream directory

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[stapelberg]: Oh, right, yes.
Or you can invoke dh_installinit with the path from the upstream directory

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Or you can invoke dh_installinit with the path from the upstream directory

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So if upstream doesn't install it, but ship it

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[question]: Yes.
So if upstream doesn't install it, but ship it

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[stapelberg]: Yeah, you could either manually copy it before, or just use what you suggest.
[question]: Yes.

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[stapelberg]: Yeah, you could either manually copy it before, or just use what you suggest.

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Any more questions?

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Great, let's move on.

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Getting your service enabled: I already mentioned that just as with update-rc.d you need to enable services

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and the easiest way, if you already have a service file shipped by upstream

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or if you put your own service file into debian/package.service

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is you add a build dependency on dh-systemd

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and then you use the dh command, which you hopefully already use

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and add the --with=systemd flag

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and then all automatically happens and it will just work.

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The maintainer scripts that are generated

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as part of that package build will contain the appropriate code

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they will call a binary called deb-systemd-helper instead of systemctl as I mentioned earlier

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which avoids having a dependency on systemd on all the packages which is probably politically not a good move.

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If you are not using dh, you can also add the dh_systemd_enable and dh_systemd_start calls directly

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in the wiki we have instructions, and the link is provided on these slides.

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To test your package -- oh, a question here?

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[question]: So you mentioned the deb-systemd-helper maintainer scripts

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I know the scope of systemd is broader than sysvinit, but

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in the sysvinit world, policy recommends

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whether or not you are using sysvinit, including other things like sysvrc or openrc or a few of the other minor ones

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(and I think also upstart) they recommend

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using invoke-rc.d and update-rc.d in debian maintainer scripts as a way of

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both abstracting from the specific system and for

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handling the case where you're debootstrapping and the daemons are not running because of policy-rc.d

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so the question is: why this instead of those

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and if policy-rc.d is configured to not start or stop, will this respect that?

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[stapelberg]: We have another of these helpers called deb-systemd-invoke which is for the invoke-rc.d part

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and it will try to respect policy. Unfortunately, policy is really hard

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It's a really horrible standard -- it's underdocumented and I had a really hard time figuring out how it works

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so it will support the use cases I could identify

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and if you have use cases that are broken please talk to me and we can try to fix it

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Also, to answer the first part of your question, update-rc.d is really hard to have a good solution in there

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we tried implementing it in there, but it turned out to not work that well, and upstream is not that responsive to our concerns.

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so we actually chose to implement a separate helper that we have under tight control and can release independently of sysvrc

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which turned out to be a much better solution because we already refactored it once and iterated on it

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quite a few times, and by now it's actually in a pretty good state.

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So that's why.

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Alright! So, to test your package, which is actually the most interesting part

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you will just install systemd, and then you can boot with the init=/bin/systemd kernel parameter

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Installing systemd does not involve breaking sysvinit or anything

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there's no conflicts in that package, you can still have both of them.

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If you just install systemd, nothing will happen.

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If you boot with init=/bin/systemd, you will actually use systemd

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so that distinction is important. You can always switch back and forth.

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So testing it is really simple. you just reboot.

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You could reboot in a vm if you don't like to reboot your main machine.

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Then what you would typically do is you check that your service starts properly on boot

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You would probably check the reload action, check stop, start, restart, and that's about it, I would say.

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because there's really not that much more to it, except if your service makes use of really advanced features and all that stuff.

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In general, I would say that your users will report bug reports if your service does not work with systemd right now

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There are plenty of users of systemd and debian that care enough to submit bug reports.

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So it's not expected of you to test it all the time

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and convert all your systems and run it all the time; a brief test will be enough.

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Now to an advanced example:

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There's actually a few more features that were maybe already mentioned if you listened to the previous talk by Lennart

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We have a nice service called debian codesearch which I happen to maintain

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And the service file is actually much more complicated.

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It not only specifies a user and a group

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It also has some arguments in here, and you can see that

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the service file format supports line wrapping, so if your command line is pretty long

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then it might make sense to wrap it and have it really nice.

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Also, we have standard output redirected to /dev/null because it's really noisy

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and mostly used for debugging. so when I feel like debugging, I can just change that to get standard output

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but in the default case I just want standard error

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Now also, my service does not actually care to log to syslog, so I say that standard error should go to the journal

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which will then end up in the syslog.

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Also, I cannot obviously exclude that there are bugs, but I also cannot sit in front of a computer 24/7 and restart my server if it crashes

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So what I want is that whenever it fails (that is, it exits with an exit code that is not 0)

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I want it to just wait a second and then restart it.

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So far I think in production I only restarted my servers once

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and then promptly fixed the bug so most of the time it's perfect, but you know: better safe than sorry!

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The other parts of the unit file are probably clear by now

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and what you will see in practice is that most of the service files really look

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kind of the same. It's pretty simple, they're pretty short

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they all use the same features.

343
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One more interesting feature that you should be aware of

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Who of you -- show of hands -- maintains a package that ships a dbus service?

345
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one or two? OK

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For the others, this is more of an academic interest

347
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but systemd can actually care about dbus-activated services

348
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so whereas dbus usually would start on its own in older versions

349
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nowadays it's better to use systemd for it

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because then it all ends up in the same hierarchy and it all gets tracked and you get all the benefits and stuff

351
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so what you do is you add Type=dbus and you specify the BusName

352
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and you don't have an [Install] section -- it's not missing on the slide, it's just not there.

353
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and then systemd will activate that service whenever that bus name is actually accessed.

354
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This is a more advanced example of the dh_systemd debhelper plugin

355
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what we do here is we install a service that should not actually be installed by default.

356
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and the way we do this is we override the dh_systemd_enable target and specify the --no-enable flag

357
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This should not be a surprise to any of you who has been using debhelper in the past

358
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I just wanted to mention it and make sure that you understand what the options are here.

359
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-- I will answer that in a second --

360
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The second example here is for the second part of the dh_systemd debhelper plugin

361
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It's dh_systemd_start

362
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and what I specify here is the --restart-after-upgrade flag which will make sure that the package does not get stopped

363
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then replaced then started, but will just get replaced and then restarted afterward

364
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which is kind of cleaner, but the package needs to support it. Question?

365
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[question]: Why do you call the dh_systemd_enable with an option of --no-enable

366
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instead of just leaving the target empty?

367
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[stapelberg]: That's an excellent question, and the comment above tries to somewhat explain it

368
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The thing is that when you purge the package

369
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if the user decided to enable it even though you ship it disabled by default

370
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then you need to clean up the symlinks

371
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So that's what dh_systemd_enable also generates maintainer scripts for

372
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So that still needs to run, so we can't just skip it.

373
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In the first version we tried, but it didn't work out.

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More questions?

375
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In the back?

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[question]: You mentioned services triggered by dbus actions

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[stapelberg]: Yes

378
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[question]: Is there a way to disable them even if the service is installed?

379
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[stapelberg]: Yes, you can mask any service. I can show you that later.

380
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One more question?

381
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[question]: So you say --restart-after-upgrade; how does restart -- I guess this is more general, but it's prompted by this

382
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how does restart work if the service is not running?

383
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[stapelberg]: That's a good question. I would have to really look it up.

384
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I think there is a try-restart action

385
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that would restart if it's running

386
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but not start it if it's not running

387
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[question]: For example, in this case you set up the service to

388
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remain disabled upon install in this example

389
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so if you install the package it is not enabled

390
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Then the user takes no action
so if you install the package it is not enabled

391
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Then the user takes no action

392
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and then they upgrade their system

393
00:26:30,930 --> 00:26:34,060
and a new version of the package is installed, it tries to restart?

394
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[stapelberg]: The thing is, as I was saying, there is a restart action in systemctl and there is a try-restart

395
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The difference is try-restart will only restart it if it's running, which probably answers your question

396
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The caveat is that

397
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currently, if you maintain a package that ships

398
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a system V initscript and a systemd service file, it will still use invoke-rc.d for the actual starting/restarting etc.

399
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And the invoke-rc.d actually has code to divert that to systemd

400
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but the problem is it's not flexible enough to use try-restart and the fancy stuff

401
00:27:07,750 --> 00:27:11,280
so this might need some actual hand-tweaking or just ignoring it for now.

402
00:27:12,320 --> 00:27:18,810
Alright! So before we enter the questions and hands-on part of this workshop

403
00:27:18,810 --> 00:27:24,090
I just want to make sure that you're all aware that we will provide help

404
00:27:24,090 --> 00:27:28,090
There is a wiki page which is linked here called https://wiki.debian.org/Systemd/Packaging

405
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which contains most of the information hopefully, or at least pointers

406
00:27:32,600 --> 00:27:38,210
We have an irc channel on irc.debian.org called #debian-systemd

407
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where you can just stop by at any time

408
00:27:40,300 --> 00:27:44,400
Most of the time there's somebody around who actually knows how to write service files and stuff

409
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There is a mailing list that we are all active and we really do mean it

410
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Please ask! Also, during debconf, if there is at any time any questions

411
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from any of you or from your friends

412
00:27:56,130 --> 00:27:59,560
please ask. we're here for answering these sorts of questions.

413
00:27:59,560 --> 00:28:03,940
Now just one more quick note: finding documentation

414
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There are manpages -- a lot of manpages

415
00:28:06,560 --> 00:28:10,860
They are roughly categorized by the sections I previously showed in service files

416
00:28:10,860 --> 00:28:14,860
So there's a systemd.service, there's a systemd.exec, etc.

417
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There's also an overview on the freedesktop.org web site (http://www.freedesktop.org/wiki/Software/systemd/) where it points to all the documentation

418
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The particularly interesting parts of that are the systemd for administrators blog series

419
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where Lennart talks about a lot of features that are interesting and how to actually make use of them in your service files

420
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And then there's a link for package repositories for the various distributions

421
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where you can just look if there already is a service file for that particular package that you maintain

422
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even though it doesn't ship one upstream

423
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So the best thing in that case would also be to adopt the service file and then also make upstream accept that.

424
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Alright! That's the talk part so far. Now I'm ready to answer any questions or look at any packages

425
00:29:00,760 --> 00:29:03,590
[question]: What are the plans for backports?

426
00:29:03,590 --> 00:29:10,080
I mean if you want to make backports to wheezy, can we use the dh_systemd helper?

427
00:29:10,080 --> 00:29:14,210
[stapelberg]: Yes, the dh_systemd helper is available in wheezy backports

428
00:29:14,210 --> 00:29:22,480
Be aware that the systemd version in wheezy is version 44, and we're currently trying to get version 204, which is much more recent

429
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into debian -- it had a version jump because of udev.

430
00:29:26,650 --> 00:29:30,550
So it's not that much more recent, it's just more recent.

431
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So there might be issues and it's up to you if you decide to commit to maintaining support

432
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for that old systemd version with your service files in wheezy, just so you know.

433
00:29:42,460 --> 00:29:49,180
If there is no immediate question, I would just go on to show you a little bit of stuff and we can answer questions as we go

434
00:29:49,180 --> 00:30:00,710
[question]: I have to prepend that at the moment I'm not maintaining any package that has to start daemons at poweron

435
00:30:00,710 --> 00:30:04,140
So I know nearly nothing about it.

436
00:30:04,140 --> 00:30:09,960
But I am a bit confused. Since I understand there are a lot of these kind of systems

437
00:30:09,960 --> 00:30:14,000
systemd, sysvinit, and so on

438
00:30:14,000 --> 00:30:20,720
As a package maintainer, what do I have to do

439
00:30:20,720 --> 00:30:24,590
if I want to support all of them, I have to provide

440
00:30:24,590 --> 00:30:29,970
the script or description file that they need for each of them

441
00:30:29,970 --> 00:30:30,910
[stapelberg]: -- to answer this, the policy mandates --
the script or description file that they need for each of them

442
00:30:30,910 --> 00:30:32,420
[stapelberg]: -- to answer this, the policy mandates --

443
00:30:32,420 --> 00:30:32,990
[question]: For example, just to complete the question, in particular if we consider just sysvinit, it is one that we have
[stapelberg]: -- to answer this, the policy mandates --

444
00:30:32,990 --> 00:30:39,180
[question]: For example, just to complete the question, in particular if we consider just sysvinit, it is one that we have

445
00:30:39,180 --> 00:30:43,080
by default, and systemd, which we are discussing now

446
00:30:43,080 --> 00:30:48,060
If I want to provide a systemd information file

447
00:30:48,060 --> 00:30:56,400
Do I also have to provide a sysvinit scripts

448
00:30:56,400 --> 00:31:02,150
or is there some compatibility layer that enables me to write one thing

449
00:31:02,150 --> 00:31:09,110
and (at least in common cases) expect some magic to make it work for other systems

450
00:31:09,110 --> 00:31:13,750
[stapelberg]: OK, I would be happy to answer that after the talk because that's not really the focus of this talk.

451
00:31:13,750 --> 00:31:18,090
So now, let me just show you a few handy things that might be useful

452
00:31:18,090 --> 00:31:22,120
I have a terminal here that you hopefully can read in the back

453
00:31:22,120 --> 00:31:26,560
Is that OK? Great! So let's just have a look at

454
00:31:26,560 --> 00:31:33,320
thinkfan.service and what I was using here is the systemctl command and you can see multiple interesting things

455
00:31:33,320 --> 00:31:36,410
First of all, it is active and running, so that's good.

456
00:31:36,410 --> 00:31:40,010
It shows that I started it 6 days ago, when I last rebooted my laptop

457
00:31:40,010 --> 00:31:45,830
It also shows the main pid, which is 2588, and that's the binary that corresponds to it.

458
00:31:45,930 --> 00:31:49,930
For more complex services, there are more binaries in the cgroup hierarchy

459
00:31:49,930 --> 00:31:53,730
What is particularly interesting for you is

460
00:31:53,730 --> 00:31:58,370
first of all, where the service file actually lives; so make sure you ship it to the correct path.

461
00:31:58,370 --> 00:32:03,710
There's also a lintian warning for that, so if you use lintian you should catch that

462
00:32:03,710 --> 00:32:07,310
It should go to /lib/systemd/system, as I mentioned

463
00:32:07,310 --> 00:32:12,730
It also should be enabled unless, of course, you decided to not enable it by default

464
00:32:14,510 --> 00:32:20,260
Now, I can just show you systemctl stop, it will be that

465
00:32:20,260 --> 00:32:25,710
[question]: the video projector does not show all of the terminal

466
00:32:25,710 --> 00:32:30,920
[stapelberg]: That is a good point. The first two columns are not shown, so let's make it like this

467
00:32:30,920 --> 00:32:32,770
Should be much better!

468
00:32:32,770 --> 00:32:37,100
Not perfect. Better?

469
00:32:37,100 --> 00:32:43,900
[question, unintelligible]

470
00:32:43,900 --> 00:32:45,910
[stapelberg]: Yeah, whatever. That's good enough.

471
00:32:45,910 --> 00:32:53,610
thinkfan.service -- now it's still enabled. It's still loaded but it's inactive because I stopped it

472
00:32:53,610 --> 00:32:58,490
I can start it again

473
00:32:58,490 --> 00:32:59,900
check that it's started

474
00:32:59,900 --> 00:33:03,370
You can also see that it used this ExecStart line

475
00:33:03,370 --> 00:33:07,270
I can also actually show you the service file. There's really no magic in here.

476
00:33:07,270 --> 00:33:14,460
There is an ExecReload directive here, so we can test if the reload actually works

477
00:33:14,460 --> 00:33:17,490
Which I need to do as root

478
00:33:17,490 --> 00:33:21,660
And then in the status output we will see that it tried to reload the service

479
00:33:21,660 --> 00:33:25,560
code=exited, status = 0/SUCCESS, so that worked.

480
00:33:25,560 --> 00:33:30,530
So those are a few simple things you can check to see if your service actually works

481
00:33:30,530 --> 00:33:36,520
10 minutes, yes. Are there any questions now? Microphone?

482
00:33:39,010 --> 00:33:48,120
[question]: The example has Type=forking. What are the other values which are valid?

483
00:33:49,030 --> 00:33:54,140
[stapelberg]: So that was obviously a suggestion to open the man page and show you that actually it is documented

484
00:33:55,590 --> 00:33:59,320
The manpage in question here is systemd.service, as I tried to explain earlier

485
00:33:59,320 --> 00:34:01,910
There's multiple Types -- there is simple

486
00:34:01,910 --> 00:34:04,900
There's forking, oneshot, dbus, notify or idle

487
00:34:04,900 --> 00:34:08,159
The most interesting ones are simple, forking, oneshot, and dbus

488
00:34:08,159 --> 00:34:11,320
dbus I already explained -- that's if you have an actual dbus service

489
00:34:11,320 --> 00:34:16,199
There's oneshot, which is for stuff like doing one thing and then nothing

490
00:34:16,199 --> 00:34:20,170
like, it's not a permanently running service, it's just a simple command like a shell script

491
00:34:20,170 --> 00:34:24,810
and then it will stay active, as in "started" afterwards

492
00:34:25,040 --> 00:34:28,570
There is forking and there is simple. The difference between simple and forking

493
00:34:28,570 --> 00:34:35,670
is that simple will -- the daemon you're starting, if it's a Type=simple one

494
00:34:35,670 --> 00:34:40,739
should just continue running in the foreground, whereas a forking one will fork itself into background.

495
00:34:40,840 --> 00:34:44,380
The preferred model is using simple because, you know, it's simple.

496
00:34:44,380 --> 00:34:48,780
forking has the implicit assumption, and I think this is important to know, that

497
00:34:48,780 --> 00:34:53,620
as long as the daemon is still running in the foreground, it's not ready

498
00:34:53,620 --> 00:34:58,830
The unit file will be considered started precisely at the moment where the daemon forks.

499
00:34:58,830 --> 00:35:03,780
That is not necessarily what your upstream software implements, but that's how it's

500
00:35:03,780 --> 00:35:05,780
[question, unintelligible]

501
00:35:05,780 --> 00:35:10,570
[stapelberg]: The question was: when it forks, or when the main process exits?

502
00:35:10,570 --> 00:35:14,770
Obviously, I think when the main process exits.

503
00:35:16,120 --> 00:35:17,390
[question]: It would be really strange in the other case

504
00:35:17,390 --> 00:35:23,140
[stapelberg]: That's how it usually works, right? You double-fork and then you exit the main process.

505
00:35:23,140 --> 00:35:25,230
More questions?

506
00:35:28,190 --> 00:35:31,520
Masking processes -- perfect, let's do that!

507
00:35:31,520 --> 00:35:35,350
So I have thinkfan and I now decide

508
00:35:35,350 --> 00:35:39,490
That it's really a shame that my fan is not spinning up as much as I would like

509
00:35:39,490 --> 00:35:44,130
So what I will just do is I will mask thinkfan.service and it will helpfully

510
00:35:44,130 --> 00:35:50,380
print out what it actually did, which is it just created a symlink in /etc/systemd/system/thinkfan.service

511
00:35:50,620 --> 00:35:51,790
pointing to /dev/null

512
00:35:53,240 --> 00:35:57,580
Essentially, it will try to load that service file but fail, because it can't read /dev/null.

513
00:35:57,580 --> 00:36:00,700
So if I now check status

514
00:36:00,700 --> 00:36:03,860
on thinkfan.service, it will tell me that it's masked

515
00:36:03,860 --> 00:36:08,370
but it's also still running. So if I now do systemctl stop

516
00:36:08,370 --> 00:36:13,280
and then status, it's now dead, and it will not be started on my next boot.

517
00:36:13,280 --> 00:36:21,110
This is different from enable and disable because it also works for dbus services and it's really like the last resort

518
00:36:21,110 --> 00:36:25,350
If you really really don't want this thing to be started, mask it. Question?

519
00:36:27,270 --> 00:36:34,500
[question]: In this case, you cannot start it by hand, you have another method implemented in systemd

520
00:36:34,500 --> 00:36:46,670
[question]: If I want it to not start at boot, but I want to be able to run it by hand

521
00:36:46,670 --> 00:36:53,190
[stapelberg]: Yes, then you obviously disable it because disable just means don't start it at boot, but you can still start and stop and restart and all that stuff

522
00:36:53,190 --> 00:36:56,620
masked is really "don't start this at all"

523
00:36:56,620 --> 00:37:02,940
So now, because I don't like loud fans, let me just unmask that

524
00:37:04,050 --> 00:37:09,700
So it told me that it deleted that symlink, and I can start it again and it will just work.

525
00:37:10,710 --> 00:37:14,110
More questions please? Over there.

526
00:37:15,750 --> 00:37:23,290
[question]: When it's active, it says "active (running)" or it says "inactive (dead)"

527
00:37:23,290 --> 00:37:29,680
Is there any particular meaning that there is a part "active" and a part in parenthesis?

528
00:37:29,680 --> 00:37:34,280
[stapelberg]: It could be "active (exited)" and that would be the case for the oneshot services

529
00:37:34,280 --> 00:37:40,230
that just fork one command, then exited, but the unit is still considered active because the command succeeded.

530
00:37:41,110 --> 00:37:42,860
More questions over here?

531
00:37:45,950 --> 00:37:52,570
[question]: Is there any support for -- what happens when a daemon dies, is it restarted, like a few times, or ?

532
00:37:52,570 --> 00:37:56,310
[stapelberg]: I actually had this on my slides earlier

533
00:37:57,350 --> 00:38:02,860
Yes: more features, here we go. You can specify RestartSec=1 and Restart=on-failure

534
00:38:02,860 --> 00:38:06,730
There's more options in that direction to restart stuff when it dies

535
00:38:07,440 --> 00:38:10,160
More questions please? Here.

536
00:38:10,830 --> 00:38:14,360
[question]: It's about the packaging

537
00:38:14,500 --> 00:38:20,520
Is it possible to use dpkg triggers -- instead we just put a file in /lib/systemd

538
00:38:20,550 --> 00:38:22,770
And then the dpkg trigger happens

539
00:38:22,770 --> 00:38:27,980
It means it will work with other packaging systems like cdbs without modification

540
00:38:27,980 --> 00:38:28,450
[stapelberg]: we actually have sent a patch to cdbs and it supports dh_systemd by now.
It means it will work with other packaging systems like cdbs without modification

541
00:38:28,450 --> 00:38:33,500
[stapelberg]: we actually have sent a patch to cdbs and it supports dh_systemd by now.

542
00:38:33,500 --> 00:38:37,090
[question]: OK, but why are you not using trigger support?

543
00:38:37,090 --> 00:38:38,170
[stapelberg]: Not using what, sorry?

544
00:38:38,170 --> 00:38:44,420
[question]: Instead of inserting a debhelper snippet in postinst

545
00:38:44,420 --> 00:38:46,640
you could have registered a trigger

546
00:38:47,820 --> 00:38:47,890
[stapelberg]: It's more complicated than that because

547
00:38:47,890 --> 00:38:49,500
[question]: It will be executed when it detects a file appearing in some allocation
[stapelberg]: It's more complicated than that because

548
00:38:49,500 --> 00:38:54,410
[question]: It will be executed when it detects a file appearing in some allocation

549
00:38:54,410 --> 00:38:57,070
[stapelberg]: Yeah, but we don't want to enable all the services by default

550
00:38:57,070 --> 00:39:00,130
And then we would need to maintain a whitelist or a blacklist of services

551
00:39:00,130 --> 00:39:02,210
and stuff, and it really needs to be more flexible than that

552
00:39:02,210 --> 00:39:04,210
OK, more questions?

553
00:39:06,410 --> 00:39:07,260
Another one?

554
00:39:08,230 --> 00:39:12,740
[question]: This time it's for services that need several instances

555
00:39:12,870 --> 00:39:14,740
Like stunnel

556
00:39:15,190 --> 00:39:16,500
[stapelberg]: Oh, multiple instances, yes

557
00:39:16,500 --> 00:39:22,620
[question]: Yes, multiple instances; usually they come with several configuration files

558
00:39:22,760 --> 00:39:26,320
And we want one instance per configuration file

559
00:39:26,320 --> 00:39:29,620
And be able to control them separately

560
00:39:29,620 --> 00:39:30,460
[stapelberg]: Yes, so there are actually --

561
00:39:30,460 --> 00:39:32,170
[question]: It's a bummer[?] to do that with sysV
[stapelberg]: Yes, so there are actually --

562
00:39:32,170 --> 00:39:34,050
[question]: It's a bummer[?] to do that with sysV

563
00:39:34,050 --> 00:39:34,170
[stapelberg]: There are good examples here of how that works. There's ifup and there's getty
[question]: It's a bummer[?] to do that with sysV

564
00:39:34,170 --> 00:39:37,280
[stapelberg]: There are good examples here of how that works. There's ifup and there's getty

565
00:39:37,280 --> 00:39:38,800
Let me just show you getty

566
00:39:38,830 --> 00:39:42,560
which has getty@tty1.service

567
00:39:42,660 --> 00:39:44,560
and what's interesting is you can see that

568
00:39:44,560 --> 00:39:47,170
the service file path actually does not include that

569
00:39:47,170 --> 00:39:49,190
so if you have a look at the service file

570
00:39:49,190 --> 00:39:51,880
You can see that it's much more complicated than I would like it to be

571
00:39:51,880 --> 00:39:56,580
But the interesting part for us is that there's %I

572
00:39:56,580 --> 00:39:59,680
which will be replaced with whatever you specify after the @

573
00:39:59,680 --> 00:40:05,590
So you can make your service file contain the @

574
00:40:05,830 --> 00:40:09,930
in the filename and then use %I and then start a specific instance of that

575
00:40:11,680 --> 00:40:15,580
[question]: And the user is expected to create all the @ files?

576
00:40:15,580 --> 00:40:17,530
[stapelberg]: Yes

577
00:40:18,170 --> 00:40:20,020
OK! More questions?

578
00:40:24,360 --> 00:40:25,100
Here.

579
00:40:26,980 --> 00:40:29,640
[question]: How about this socket-based activation?

580
00:40:29,640 --> 00:40:31,920
[stapelberg]: Socket activation -- that is a good question!

581
00:40:31,920 --> 00:40:37,640
Let me just have a look if I have any socket activation files lying around here

582
00:40:37,640 --> 00:40:42,350
I have approx.socket, which seems kind of appropriate for this conference.

583
00:40:43,460 --> 00:40:45,880
Socket activation essentially works like this, where you have

584
00:40:45,880 --> 00:40:49,070
[Socket] instead of [Service] in your service file

585
00:40:49,950 --> 00:40:51,160
In your socket file, sorry

586
00:40:52,130 --> 00:40:55,120
You specify a TCP port

587
00:40:55,120 --> 00:40:57,850
or a unix socket or whatever it should listen on

588
00:40:57,850 --> 00:41:00,240
And then there is Accept=yes

589
00:41:00,240 --> 00:41:02,760
where the default is Accept=no

590
00:41:02,760 --> 00:41:07,160
The difference is that Accept=yes mimics the inetd-style behavior

591
00:41:07,160 --> 00:41:10,590
of just starting one process per connection, which is kind of wasteful

592
00:41:10,590 --> 00:41:14,090
and the actual real good socket activation is

593
00:41:14,090 --> 00:41:17,790
not having that, but patching the service to

594
00:41:17,790 --> 00:41:21,350
when being started, inherit the file descriptor

595
00:41:21,350 --> 00:41:25,960
of the socket and then just integrate it in its event loop and handle that.

596
00:41:25,960 --> 00:41:28,380
And many services are already patched for that.

597
00:41:28,650 --> 00:41:32,750
Some of them are patched, but not in debian, and some of them you would need to patch.

598
00:41:32,750 --> 00:41:35,310
But this is really a thing of like an hour or two.

599
00:41:35,310 --> 00:41:37,260
I did it for bacula once, for example.

600
00:41:38,400 --> 00:41:39,680
OK. Question over here?

601
00:41:42,200 --> 00:41:46,300
[question]: So the socket file just includes information about where to listen

602
00:41:46,300 --> 00:41:51,350
And if to accept or not, or to start. Is that just in the service file then?

603
00:41:51,350 --> 00:41:55,620
[stapelberg]: Yes, the socket file has to match, by name, the service file

604
00:41:55,620 --> 00:42:00,860
And because I used Accept=yes, it needs to be approx@.service, not approx.service

605
00:42:00,860 --> 00:42:06,910
And then this will in turn just take the standard input from the socket, like inetd does, and start it up.

606
00:42:07,990 --> 00:42:08,860
One more question?

607
00:42:08,860 --> 00:42:12,230
[question]: Why do I have to add the @?

608
00:42:12,230 --> 00:42:20,800
[stapelberg]: Because if you use inetd-style stuff, then for every incoming new connection it will start a separate process.

609
00:42:20,800 --> 00:42:20,870
so all these processes show up in your cgroup hierarchy.
[stapelberg]: Because if you use inetd-style stuff, then for every incoming new connection it will start a separate process.

610
00:42:20,870 --> 00:42:23,190
so all these processes show up in your cgroup hierarchy.

611
00:42:23,460 --> 00:42:25,840
So that's why the instance is used in this case.

612
00:42:25,840 --> 00:42:33,210
Does that also relate to ExecStart=- instead of directly the path?

613
00:42:33,380 --> 00:42:36,940
No, in fact, I already looked at this and wondered why it is there

614
00:42:36,940 --> 00:42:41,780
I think it should not be there, because the - means that failures should be ignored.

615
00:42:41,780 --> 00:42:45,780
I'm not entirely sure why it makes sense to have it here

616
00:42:45,780 --> 00:42:49,480
My suspicion would be that if there's a connection and then it goes away

617
00:42:49,480 --> 00:42:53,450
then it shouldn't -- I would need to look that up. Sorry, no answer.

618
00:42:53,450 --> 00:42:56,910
More questions? Last question, we have one minute left.

619
00:42:56,910 --> 00:42:58,830
Last question over there.

620
00:43:04,650 --> 00:43:10,100
[question]: Thank you. Where are dependencies defined in this thing?

621
00:43:10,100 --> 00:43:15,240
[stapelberg]: Oh yes, that's a good question. Ideally, dependencies are not defined anywhere because they are implicit by socket activation.

622
00:43:15,240 --> 00:43:19,340
In case that's not the case, for example, if my

623
00:43:19,340 --> 00:43:24,490
-- I think I should probably have it here, let me just have a look real quick --

624
00:43:26,500 --> 00:43:33,430
dcs-web.service, it's actually more complicated. No it doesn't have it.

625
00:43:33,430 --> 00:43:40,090
So there is, in the [Unit] section, where we also specified the Description, there can be a Before= and After=

626
00:43:40,090 --> 00:43:44,930
So in my case, I would start codesearch after postgresql came up

627
00:43:44,930 --> 00:43:47,920
and I would just specify After=postgresql.service

628
00:43:47,920 --> 00:43:51,660
You can specify multiple services there, you can specify the directive multiple times

629
00:43:51,660 --> 00:43:55,520
But usually it should not be required to specify dependencies, which is nice.

630
00:43:55,660 --> 00:43:57,520
OK, thank you.

631
00:43:57,610 --> 00:44:01,100
OK, time is over. I would like to say, thank you very much for your attention.

632
00:44:01,100 --> 00:44:03,630
If you have any questions, please let me know and we can fix it.

633
00:44:03,630 --> 00:44:05,120
[talkmeister]: Thank you, Michael.

634
00:44:05,120 --> 00:44:05,860
[clapping]
[talkmeister]: Thank you, Michael.

635
00:44:05,860 --> 00:44:10,430
[clapping]