[CentOS] Just need to vent

Tue Jan 26 16:18:16 UTC 2016
Chris Adams <linux at cmadams.net>

Once upon a time, Peter Duffy <peter at pwduffy.org.uk> said:
> Ultimately it's all software, and software can be
> written/changed/updated to do anything required - all that's needed is
> the skill and the motivation.

Well sure, and I can build a rig to replace a wheel on your car while
you're driving down the highway; doesn't mean it is practical to do so.
You could also build a distribution with both Linux and FreeBSD kernels
(and IIRC somebody tried with Debian), but that doesn't mean it is a
practical thing, especially for a comercially-supported, long-term
distribution like RHEL.

> If systemd is so "core" that it can't be
> unplugged and plugged easily, and glues together a lot of otherwise
> unrelated components,  then it's just bad software - end of story

Nope.  I said "the init system" is core, not "systemd".  Someone
building a coherent distribution has to make choices about what is
practical to support (and nobody has unlimited man-hours to build magic
tools that can swap out init systems with zero outside impact).  And
once you include systemd, there are features that it makes sense to take
advantage of, rather than ignore because somebody has a "multiple init
systems" requirement.

Sun and Apple already figured out that a "know nothing" super-simple
init didn't handle all that was really needed for a modern OS.  The
Linux world had some earlier attempts, like Upstart (used in RHEL 5 and
6 IIRC), but it never got the critical mass to use its functionality
(and IIRC fairly early on, it became apparent it took some wrong

The init system being PID 1 does have a bunch of "magic" abilities on a
Unix-like system, so trying to strip it down to a minimal thing turns
out to not be the best approach.  Of course, a lot of the crap that is
in systemd-the-package (and there is a bunch, although RHEL ignores some
of that at least for now) is not in PID 1.

> - parallel startup of services. Not sure that I'd want that anyway - too
> much risk of two services trying to grab the same resource at the same
> time - I'm absolutely happy with the sysvinit approach of one service
> startup completing/failing before the next one happens. That way, things
> are nice and orderly.

So, the parallel startup has shown a few issues along the way, where
there were undefined dependencies.  There have always been dependency
issues with SysV-style init - service deps can't always be described
properly as an ordered list, more of a directed graph (which systemd's
unit files allow and handle).  Was it annoying if you encountered such a
bug?  Yes, but those types of bugs came up with SysV-style init
repeatedly over the years anyway.  You had poor solutions like init
scripts calling other init scripts to make sure they had the things they
needed (and "soft" deps, like on a database server, were really a mess).

For example, AFAIK it is still the case that RHEL 6 and before don't
enable quotas on a filesystem on an iSCSI device.  The only way to "fix"
that would be to copy all the quota code from rc.sysinit to another,
post-netfs, script.  With systemd, I'm pretty sure the same quota unit
can re-trigger after new filesystems are "discovered".

On the flip side, when I need to add a new one-off service, I can write
a dozen line (or more often less) systemd unit file much easier than
writing an init script.  All the odd corner cases are handled for me, I
don't have to worry about something like daemontools if I want the
service restarted on fail (one line in the unit file), standard out
and/or error can be redirected to log files (without having to pipe to
logger), etc.

> As we all know (don't we just?) sysadmin work and responsibilities are
> heavy, and frequently eat into evenings, nights, weekends and
> (so-called) holidays. Anything which increases the sysadmin workload -
> e.g. suddenly faced with a vertical learning curve just to do the tasks
> they did yesterday

Okay, but change is the only constant in this business.  I agree you
should not be running into the learning curve significantly on
production systems, but if you are running systems with thousands of
users, you should always be looking ahead to new technologies all the
time.  I've always worked in the Internet service provider "world"; when
I started, a T1 and a router you could fit in a backpack made you an
ISP.  Now we have a router that is a third of a rack, requires a lift to
move, with a couple of 10 gig ethernet links to the world, and that's
still considered a "small" ISP.

It is so much easier now to lab up new versions for testing and learning
(just fire up some VMs).  If you want to have an idea of "what is
coming", run some Fedora releases now and then.  I personally have used
Fedora on my desktop since the project started (and Red Hat Linux for
many years before that).

It is called professional education; lots of jobs require you to learn
new skills on an on-going basis.

I've been running CentOS 7 on all my new server installs for a year now.
Is it perfect?  No, but I haven't seen the perfect OS yet.  Am I still
learning?  Yes, always.  Do I think it is worth the higher learning
steps than say from CentOS 5->6?  Yes, I do.

Chris Adams <linux at cmadams.net>