ab - Apache HTTP server benchmarking tool looks like a pretty nifty little command for performance testing and troubleshooting an Apache server from the Unix command line.

It has a large number of options, but this seems like a good combination to start with:
Code:
ab -kc 10 -t 30 http://localhost/
These settings mean:

-k (enable KeepAlive)
-c10 (perform 10 requests concurrently)
-t30 (limit the testing time to 30 seconds)
On my server, this produced the following output:
Code:
This is ApacheBench, Version 2.3 <$Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking localhost (be patient)
Completed 5000 requests
Completed 10000 requests
Completed 15000 requests
Completed 20000 requests
Completed 25000 requests
Completed 30000 requests
Completed 35000 requests
Completed 40000 requests
Completed 45000 requests
Completed 50000 requests
Finished 50000 requests


Server Software:        Apache/2.2.11
Server Hostname:        localhost
Server Port:            80

Document Path:          /
Document Length:        313 bytes

Concurrency Level:      10
Time taken for tests:   14.476 seconds
Complete requests:      50000
Failed requests:        0
Write errors:           0
Non-2xx responses:      50008
Keep-Alive requests:    49511
Total transferred:      29583222 bytes
HTML transferred:       15652504 bytes
Requests per second:    3454.03 [#/sec] (mean)
Time per request:       2.895 [ms] (mean)
Time per request:       0.290 [ms] (mean, across all concurrent requests)
Transfer rate:          1995.73 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.4      0      10
Processing:     0    3   2.0      3      93
Waiting:        0    3   2.0      3      93
Total:          0    3   2.1      3      93

Percentage of the requests served within a certain time (ms)
  50%      3
  66%      3
  75%      3
  80%      3
  90%      4
  95%      4
  98%      6
  99%      8
 100%     93 (longest request)
The next task is to make server changes and monitor their effects on performance.

This tool is especially useful because it can be run directly on your web server, which enables you to separate server performance issues from network performance issues.