/var/lock Locking StandardsSo it looks like /var/lock has been a thing since 2004 and I just
missed it.
“Filesystem Hiearchy Standard” /var/lock has been specified at least
since 2004. Here is the current (2015) spec. It even includes how the
PID should be stored with a newline. It is different how I would have
expected it =>
https://refspecs.linuxfoundation.org/FHS_3.0/fhs-3.0.html#varlockLockFiles
However, I have also lock files in my home directory and in
$XDG_RUNTIME_DIR.