/var/run/dmesg.boot

/var/run/dmesg.boot file contains the FreeBSD boot messages, and this is very helpful for checking hardware related info: 

  1. # cat /var/run/dmesg.boot | grep -i CPU
  2. CPU: Intel(R) Core(TM) i5-4310U CPU @ 2.00GHz (2594.03-MHz K8-class CPU)
  3. cpu0: <ACPI CPU> on acpi0

Because the capacity of system message buffer is limited, FreeBSD employs /var/run/dmesg.boot in case the content of buffer is flushed.

References:
Devices and Device Nodes;
Back To Basics: Unix Differences in Performing Tasks.