/run or /tmp
What's the difference between /run and /tmp?
"The purpose of /run is to store transient files: those that contain runtime information, which may need to be written early in system startup, and which do not need to be preserved when rebooting."
This directory is used to store temporary files, and can be accessed by any user or application."
One is for "transient files" (existing, happening, or staying somewhere for a short period of time only) and one is for "temporary files" (existing, done, or used for only a limited period of time).
Why don't all the distros simply use /tmp?