Re: [gentoo-user] Re: systemd? [ Was: The End Is Near ... ]

[Pandu Poluan]

On Mar 18, 2012 8:48 AM, "Canek Peláez Valdés" <caneko@×××××.com> wrote:
>
> On Sat, Mar 17, 2012 at 6:48 PM, Nikos Chantziaras <realnc@×××××.com>
wrote:
> > On 17/03/12 13:53, Alan Mackenzie wrote:
> >>
> >> Hello, Nikos.
> >>
> >> On Sat, Mar 17, 2012 at 08:25:48AM +0200, Nikos Chantziaras wrote:
> >>
> >>>> Happy Computer Users, systemd is on your horizon.
> >>
> >>
> >>> No, we don't.  I hope systemd arrives soon.  It's the best init
system I
> >>> ever saw.
> >>
> >>
> >> What's so good about it?  What will it do for me?
> >>
> >> I have this horrible sneaking suspicion that it will be more
complicated
> >> than /sbin/init + OpenRC, just like udev + initramfs is more
complicated
> >> than udev, and CUPS is more complicated than classical lpr.
> >>
> >> Why do you find it so good?
> >
> >
> > No idea.  I only posted this because the OP didn't say what's bad about
> > systemd :-)  I really don't know I should care whether my system runs
OpenRC
> > or systemd.
>
> Take this with a grain (or a kilo) of salt, since I'm obviously
> biased, but IMHO this are systemd advantages over OpenRC:
>
> * Really fast boot. OpenRC takes at least double the time that systemd
> does when booting, easily verifiable. In my laptop systemd is twice as
> fast as OpenRC; in my desktop is three times faster.
>
> * Really parallel service startup: OpenRC has never been reliable on
> parallel service startup; its documentation says it explicitly.
>
> * Really simple service unit files: The service unit files are really
> small, really simple, really easy to understand/modify. Compare the 9
> lines of sshd.service:
>
> $ cat /etc/systemd/system/sshd.service
> [Unit]
> Description=SSH Secure Shell Service
> After=syslog.target
>
> [Service]
> ExecStart=/usr/sbin/sshd -D
>
> [Install]
> WantedBy=multi-user.target
>
> with the 84 of /etc/init.d/sshd (80 without comments).
>
> * Really good documentation: systemd has one of the best
> documentations I have ever seen in *any* project. Everything (except
> really new, experimental features) is documented, with manual pages
> explaining everything. And besides, there are blog posts by Lennart
> explaining in a more informal way how to do neat tricks with systemd.
>
> * Really good in-site customization: The service unit files are
> trivially overrided with custom ones for specific installations,
> without needing to touch the ones installed by systemd or a program.
> With OpenRC, if I modify a /etc/init.d file, chances are I need to
> check out my next installation so I can see how the new file differs
> from the old one, and adapt the changes to my customized version.
>
> * All the goodies from Control Groups: You can use kernel cgroups to
> monitor/control several properties of your daemons, out of the box,
> almost no admin effort involved.
>
> * It tries to unify Linux behaviour among distros (some can argue that
> this is a bad thing): Using systemd, the same
> configurations/techniques work the same in every distribution. No more
> need to learn /etc/conf.d, /etc/sysconfig, /etc/default hacks by
> different distros.
>
> * Finally, and what I think is the most fundamental difference between
> systemd and almost any other init system: The service unit files in
> systemd are *declarative*; you tell the daemon *what* to do, not *how*
> to do it. If the service files are shell scripts (like in
> OpenRC/SysV), everything can spiral out of control really easily. And
> it usually does (again, look at sshd; and that one is actully nicely
> written, there are all kind of monsters out there abusing the power
> that shell gives you).
>
> These are the ones off the top of my head; but what I like the most
> about systemd is that it just works, and that it makes a lot of sense
> (at least to me).
>
> Most of systemd features can be implemented in OpenRC (although the
> speed difference will never be eliminated if OpenRC keeps using shell
> files). My question is: why bother? systemd is already here, it
> already works, and it's actually supported in Gentoo.
>
> But again, remember that I'm biased: I keep an overlay to run Gentoo
> systems with only systemd; no OpenRC, no baselayout, no SysV. You guys
> can try it if you want:
>
> http://xochitl.matem.unam.mx/~canek/gentoo-systemd-only/
>
> Usual disclaimer: I take no responsibility if using my overlay results
> in your systems asploding. That said, I'm using it on all my machines
> without a hitch.
>
> Regards.

Interesting...

However, what if the service is complex? For example, I created a
"gatewall" service which, upon boot, initializes :

* Routing tables and the RPDB
* ipset
* iptables

while ensuring that upon shutdown, the settings of the above are
(optionally) saved.

How do I specify such intelligence?

Rgds,