So are Xorg and Apache HTTPD, which break module ABI with every release. Postfix and qmail are also monolithic (according to your reasoning), with a modular implementation of multiple processes but no stable interface between them. If you replace of the postfix processes with one of the qmail processes you won't get a working MTA.
Not to mention the Linux, FreeBSD, Solaris etc. kernels themselves.
Why is it then that we see this argument only used against systemd, when your average Linux distro install is primarily composed of software systems that you would consider to be monolithic?
> Moreover they are also tightly coupled to kernel features.
sysvinit is also tied to kernel features: it won't work without Linux procfs.
> dbus is this weird text/binary RPC-ish mix which is not documented.
No idea where you got that idea, is this D-Bus protocol documentation is a figment of my imagination?
Here's a nice quote right from the doc you linked: The D-Bus protocol is frozen (only compatible extensions are allowed) as of November 8, 2006. However, this specification could still use a fair bit of work to make interoperable reimplementation possible without reference to the D-Bus reference implementation.
The fact that you even NEED a (crappy) doc is a sign it doesn't use the Unix design philosophy.
In contrast, look at the Debian Control File format, which apt metadata is stored in. I parsed and wrote a dependency resolver for it WITHOUT any reference to docs. The format is self-documenting text.
X is Unix style in the sense that you can plug in different window managers, but not Unix style in other ways.
Shared library extension modules (e.g. Apache, Python, etc.) are not "classic" Unix. Classic Unix simply didn't have shared libraries (or threads). Plan 9 and Go explicitly have this heritage; they don't support shared libraries.
Apache is Unix style because it uses stable protocols between application and server, like CGI, FastCGI, etc. It also uses textual logs, unlike systemd.
I would also argue that systemd encompasses more diverse functionality than either X or Apache, which is saying a lot. The bigger a system is, the worse a monolithic architecture is.
But you're right that modern Unix doesn't follow Unix style in many ways. I am not arguing for purity -- shared libraries are useful, and graphics don't fit well within Unix style. But I do think it is worth understanding the Unix style, for very a practical reason. That reason being: you simply end up with less code when your systems are modular and composable.
Oh right, somebody looked at the spec for 15 minutes, mis-read it completely (confusing the authentication protocol with the actual IPC protocol) and wrote a blog rant about their failure in reading comprehension. Very compelling.
> The fact that you even NEED a (crappy) doc is a sign it doesn't use the Unix design philosophy.
So HTTP is against the UNIX philosophy too? Or did you also happen to implement that without ever looking at the specification?
> In contrast, look at the Debian Control File format, which apt metadata is stored in.
In other words, apples make better apple juice than oranges.
> That reason being: you simply end up with less code when your systems are modular and composable.
You seem to be under the mis-apprehension that monolithic is somehow an antonym of modular. systemd is both modular and monolithic (in your meaning of that term).
> Why is it then that we see this argument only used against systemd
WIth systemd we see the changes against Unix design, whereas your other examples already exist.
That aside, poking around I found this: http://www.freedesktop.org/wiki/Software/systemd/InterfacePo... which looks like reasonably well-defined interfaces?
Also not really seeing the problem with a binary protocol, works fine for tcp/ip.
If you have ONLY used Unices, then I could understand why the philosophy is invisible.
If, like me, you had used Windows exclusively for a decade, and then Unix for a decade, then the Unix philosophy would knock you up side the head. The systems could not be more different. (Despite the fact that they run mostly the same applications. http://www.joelonsoftware.com/articles/Biculturalism.html is the review that got me to read it).
One of the best books on the Unix philosophy is "The Art of Unix Programming", which is available for free. (I recommend getting a hard copy and reading the whole thing.)
http://www.catb.org/esr/writings/taoup/html/
Other books include The Unix Programming Environment by Pike et. al., though it's less explicit about the philosophy.
Here's one part of the argument: systemd breaks the Unix design style because it's monolithic: http://www.catb.org/esr/writings/taoup/html/ch01s06.html#id2...
But then systemd developers claim it's not monolithic because it's actually composed of multiple processes. They say there is a misconception that all code is contained in PID 1. There are many executables and many processes, so they would say systemd is modular.
But the problem is that all the binaries are released together, without well-defined interfaces. Moreover they are also tightly coupled to kernel features.
If you have 2 binaries A and B, but the interfaces between them is not documented or stable, then it's not really modular, because you can't write your own B' to work with A or A' to work with B.
The recent thread here about dbus is a good example. Traditional Unix is simple text protocols. dbus is this weird text/binary RPC-ish mix which is not documented.
There are lots of other issues with systemd and the Unix philosophy, but that should give you a flavor.