No OS I've used in the last ~10 years left a core dump by default. Maybe longer, but I didn't know what core dumps were then, so I wouldn't know what I was looking at if they did.

Almost all Unixes generate coredumps by default. illumos, FreeBSD, and yes GNU/Linux. The reason why you might not have seen coredumps in a cores/ directory is because most GNU/Linux distributions have configured the kernel such that all new coredumps are sent to a processing script (systemd has a coredump script) which results in a coredump file not included in the current directory.

A bunch of the Unixes I've worked with do, it seems like. And at least some of the Linux systems on my own computers (I'm almost positive that this was my first contact with the idea of a core dump).

Do you have coredumps enabled on your hosting servers? As written in the blogpost the major distributions have a configuration that will forward coredumps to crash handling tools and not directly store them. Others simply have coredumps disabled by default.

It depends on how you are running it, in my experience. We're forced, due to ISP restrictions, to use FastCGI. I've not tested this theory, so YMMV, but I've had more trouble doing it that way than when using PHP as a module. We've seen less of it over the past few years, but it happened regularly enough in the past to make "grep for coredumps" a regular task.

It's easy to make PHP segfault. All you have to do is create an infinite recursion.

Unless you use xdebug.max_nesting_level

Xdebug in production you say?

It's not hard to make PHP seg fault and in the course of doing web development and hosting you will need to use core files to debug opaque issues with GDB.

I've had to do this ~3 times in the last couple years. In all cases it was extensions not playing well (xcache, gmagick/imagick). I actually couldn't find a single version of gmagick/imagick that tore down or something properly in php 7.0.x (broke when phpunit launched extra-process tests, among other places)

I've always found the cause to be extensions as well. Usually a version conflict or something. It's so difficult to debug though. Always takes a while just to get everything you need to finally dig in.

I've experienced one or two over twelve years, usually due to a new version and always caught in dev. PHP crashes are incredibly rare.