Re: [gentoo-amd64] Please get me straight about sysvinit vs. systemd, udev vs eudev vs mdev, virtuals and other things...

[Mark Knecht]

Hi Canek - good to hear from you.

On Sun, Mar 2, 2014 at 9:45 AM, Canek Peláez Valdés <caneko@×××××.com> wrote:
> On Sun, Mar 2, 2014 at 10:57 AM, Mark Knecht <markknecht@×××××.com> wrote:
>> Hi all,
>>    I'd like to check in and get some education concerning future
>> configuration of my Gentoo machines. Thanks in advance.
>>
>>    In the last few days there is a news announcement about needing to
>> change kernel my configuration to enable CONFIG_FHANDLE to support
>> udev-210. I'm currently at udev-208 and virtual/udev-208-r1 so no big
>> deal yet. However reading the news announcement it appears this has
>> more to do with systemd than anything else and I don't use systemd so
>> does/will this effect my machines?
>
> Yes, it will; udev (independently of systemd) is using FHANDLE to find
> the devices in the computer.
>
> udev is part of systemd, but it can be used separately. This is
> supported by upstream (i.e., systemd). The change in the kernel config
> is needed by udev.
>

So as an end user type I'm a little confused by this part of your
response. When you say udev is 'part of systemd' do you mean at the
project level? That's what I understand from your longer response
below.

>>    NOTE: I have no problem I know about today enabling CONFIG_FHANDLE
>> if it's recommended.
>
> It is: udev will not work without it. Even more: eudev (when they
> catch up) will not work without it either, since eudev does no
> original work; they just exorcise systemd from udev.
>

Good to know and I've already read a little more about it and enabled
it in my kernel.

>>    That said there's an interesting (if it is to be believed) little
>> rant thread over the last couple of days on LKML about Debian
>> leadership forcing people into systemd.
>
> The Debian Technical Committee took the technical decision of using
> systemd as default init system. There is no "forcing" here; Debian is
> ruled by a Constitution, and they (very slowly) followed their rules
> and laws to reach that decision.
>
>> I think the Gentoo devs forked
>> udev to make either mdev or eudev but when it was announced it was too
>> new for me so I just let it go by.
>
> Gentoo, by default, uses udev without systemd. Again, this is
> supported by upstream (i.e., systemd), nothing special about it.
> *Some* Gentoo developers "forked" systemd  into eudev, so you can have
> a "udev without systemd" (although, as stated above, upstream supports
> udev without systemd). I don't know the exact numbers, but it's my
> impression (by reading -dev and -user), that eudev is used in Gentoo
> (and only Gentoo) by a handful of people. The great majority is using
> sys-fs/udev, and I'm willing to bet that more people are using systemd
> directly than eudev.
>
>> Maybe now it's time for me to look
>> into making a change of some type? I see eudev in portage, but not
>> mdev.
>
> Using eudev will gain you nothing; the FHANDLE change will reach them
> eventually. If you use mdev, you will have a noticeable loss of
> functionality. I think even less people use mdev than eudev.
>
>>    A (really, really, really) quick scan of the current install docs
>> makes me think sysvinit/OpenRC/udev is still the default for new
>> installs. Is this true?
>
> Yes, it's true, and no one will propose changing this, at least in the
> near future. And even if systemd becomes the standard Gentoo init
> system, OpenRC will be (almost surely) supported until the end of
> times.
>
>> If so why is this kernel change being
>> required?
>
> Because is new functionality provided by the kernel required by
> *udev*, not (necessarily) systemd. Happens all the time; new
> technology in the kernel is pretty useless if userspace doesn't start
> taking advantage of it.
>

Understood.

>>    Also, I seem to have virtual/udev installed which says it's about
>> enabling switching between udev & eudev. However there are no files
>> associated with virtual/udev. (equery files virtual/udev returns
>> nothing)
>
> That's why it's a virtual; a virtual pulls in different
> implementations of the (in theory) same functionality.
>
>> It appears I cannot install eudev without removing udev so
>> this seems a big step to take:
> [ snip]
>
> It is a big step to take, and it will gain you nothing: eventually,
> eudev *will* require FHANDLE, unless they diverge even more from
> upstream, a thing I believe they cannot afford to do.
>
>>    At this point I'm not even sure what my other questions might be as
>> I'm just trying to get my head around what others are using these
>> days.
>
> Well, it's undeniable that systemd usage is on the raising everywhere,
> including Gentoo (specially since GNOME pulls it in). I myself use
> systemd, and could not be happier.
>
> However, OpenRC is (and will be for the foreseeable future) the
> default init system.

Humm. OK, so I've updated my main spinning rust kernel for FHANDLE. No
problems there. sysvinit/OpenRC/udev. All good.

As I write this I'm in my SSD backup Gentoo install. I haven't used it
in awhile so I'm emerging 668 packages. System setup as above but
maybe I'll consider switching this one to systemd just as a trial. At
this time it's not important on my personal machines. However my 86
year old father is the last Gnome holdout in the family. I've not
updated his box in quite awhile (cognitive issues, fewer GUI changes
are better for him) However if I do update then it will likely be
Gnome so having at least a little experience with systemd might be
good.


>> I do have a second Gentoo install on this system on an SSD so
>> (once updated) I could do a switch there as a test.
>
> My suggestion is for you to enable FHANDLE. From the kernel:
>
<SNIP>

Done, no noticeable impact after 20 minutes. All good.

>
> So just enable the thing and go on with your life.
>
> My 0.02 ${CURRENCY}.
>
> Regards.
> --
> Canek Peláez Valdés
> Posgrado en Ciencia e Ingeniería de la Computación
> Universidad Nacional Autónoma de México
>

Again, THANKS for a wonderful response with lots of good information.
We're lucky to have you as one of the long-time Gentoo guys. I for one
greatly appreciate what little I understand. :-)

Cheers,
Mark