Origin of /var/run contents
Wheezy used sysvinit and related pacakges, not systemd. Jessie does
have the file-hierarchy(7) man page that Jonathan mentioned.
Debian 7 had systemd, and the sharp-eyed who read the URL will have
noticed that I pointed to the Debian 7 version of that manual page.
Have a manual page from Ubuntu 14, which likewise did in fact have
systemd, to go with it:
This stuff does go back quite a number of years, now.
The sharp-eyed will have also spotted that that is untrue. At least one
of the things that I pointed to most definitely is not systemd.
All of the stuff Jonathan is describing is from systemd,