That link is really interesting! Thanks for that. I should have probably said procfs is Linux-specific. Anyway, learned (rather unlearned) something new today.
Also interesting is that early Unix systems (before v8) used `ptrace()` for gathering process information - the same system call programs like strace/ltrace use today.
No, procfs is also not Linux specific ;-) /proc is a filesystem, so most of us refer to it as 'procfs' for short. In fact, the header file you include a C program in Solaris to use it is '<procfs.h>'.
As I said before, the only thing that's really Linux-specific is Linux chose to represent it as text instead of something machine-parsable.
https://www.usenix.org/memoriam-roger-faulkner
...and there's a general history here:
https://blogs.oracle.com/eschrock/entry/the_power_of_proc
The part that may be specific to Linux is Linux provides a text-based interface, whereas systems like Solaris provide a binary interface.