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

[Canek Peláez Valdés]

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.
-- 
Canek Peláez Valdés
Posgrado en Ciencia e Ingeniería de la Computación
Universidad Nacional Autónoma de México