This section concludes our look at performance monitoring and tuning on Unix systems. It contains a brief introduction to network performance, a very large topic whose full treatment is beyond the scope of this book. Consult the work by Musameci and Loukides for further information.
netstat -s command is a good place to start when examining
networkperformance. It displays network statistics. You can
limit the display to a single network protocol via the
-p option, as in this example from an HP-UX
netstat -s -p tcpOutput shortened. tcp: 178182 packets sent 111822 data packets (35681757 bytes) 30 data packets (3836 bytes) retransmitted 66363 ack-only packets (4332 delayed) 337753 packets received 89709 acks (for 35680557 bytes) 349 duplicate acks 0 acks for unsent data 284726 packets (287618947 bytes) received in-sequence 0 completely duplicate packets (0 bytes) 3 packets with some dup, data (832 bytes duped) 11 out of order packets (544 bytes) 5 packets received after close 11 out of order packets (544 bytes)
The output gives statistics since the last boot.
Network operations are proceeding nicely on this system. The highlighted lines are among those that would indicate transmission problems if the values in them rose to appreciable percentages of the total network traffic.
More detailed network performance data can be determined via the various network monitoring tools we considered in Section 8.6.