Given /run's adoption and rationale [1] and a number of autotools based projects that need to refer to their PID or other run-time data that typically appears in /var/run (e.g. libvirt). There should be a good standardized way to specify the path for the run-time data. Currently many use localstatedir + "/run", which results in PREFIX/var/run by default. Most distro build systems set localstatedir to /var, resulting in /var/run. However that is not the correct directory and its relying on the fact that popular distros are currently providing a symlink from /var/run to /run. The reality is that configure should add --rundir to allow Linux distros to set it to /run and for other platforms that have not adopted /run, they could continue to use /var/run.
Hopefully this makes sense but if you need more information or rationale I'll be glad to discuss this further.
Thank you.
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Doug Goldstein