We recently introduced a new agent flag for --runtime_dir. Unlike the --work_dir, this directory is designed to hold the state of a running agent between subsequent agent-restarts (but not across host reboots).
By default, this flag is set to /var/run/mesos since this is a tempfs on linux that gets automatically cleaned up on reboot. When running as non-root we set the default to os::temp()/mesos/runtime.
We should call this out in the CHAGNELOG