OpenBSD Generic Health checks

TCP Statistics

There are some counters in netstat -sptcp output. In particular:

        532358 SYN packets dropped due to queue or memory full
        770174566 SYN cache entries added
                0 hash collisions
                768118448 completed
                6 aborted (no space to build PCB)
                905577 timed out
                0 dropped due to overflow
                0 dropped due to bucket overflow
                1150155 dropped due to RST
                0 dropped due to ICMP unreachable
        7036108 SYN,ACKs retransmitted
        13117384 duplicate SYNs received for entries already in the cache
        2580 SYNs dropped (no route or no space)

Detect select() collisions

http://www.tedunangst.com/flak/post/select-works-poorly

sysctl kern.nselcoll