ab（apache bench）是apache下的一个工具，主要用于对web站点做压力测试，

基础用法：
-c选项为一次发送的请求数量，及并发量。
-n选项为请求次数。
实际测试效果：

[dev@web ~]$ ab -c 20 -n 50000 http://www.landui.com/
This is ApacheBench, Version 2.3 <$Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.landui.com/
Licensed to The Apache Software Foundation, http://www.landui.com/
Benchmarking 192.168.1.210 (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: nginx/1.6.2
Server Hostname: 192.168.1.210
Server Port: 80
Document Path: /
Document Length: 41005 bytes # 请求的页面大小
Concurrency Level: 20 # 并发量
Time taken for tests: 1180.733 seconds # 测试总共耗时
Complete requests: 50000 # 完成的请求
Failed requests: 0 # 失败的请求
Write errors: 0 # 错误
Total transferred: 2067550000 bytes # 总共传输数据量
HTML transferred: 2050250000 bytes
Requests per second: 42.35 [#/sec] (mean) # 每秒钟的请求量。（仅仅是测试页面的响应速度）
Time per request: 472.293 [ms] (mean) # 等于 Time taken for tests/(complete requests/concurrency level) 即平均请求等待时间（用户等待的时间）
Time per request: 23.615 [ms] (mean, across all concurrent requests) # 等于 Time taken for tests/Complete requests 即服务器平均请求响应时间 在并发量为1时 用户等待时间相同
Transfer rate: 1710.03 [Kbytes/sec] received # 平均每秒多少K，即带宽速率
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 1 18.5 0 1001
Processing: 38 471 534.1 155 9269
Waiting: 37 456 524.6 147 9259
Total: 40 472 534.5 155 9269
Percentage of the requests served within a certain time (ms)
50% 155
66% 571
75% 783
80% 871
90% 1211
95% 1603
98% 1839
99% 2003
100% 9269 (longest request)

上边只记录了一些常用参数，其他参数介绍这里也贴一下：
Usage: ab [options] [http[s]://]hostname[:port]/path
Options are:
-n requests Number of requests to perform
-c concurrency Number of multiple requests to make
-t timelimit Seconds to max. wait for responses
-b windowsize Size of TCP send/receive buffer, in bytes #
-p postfile File containing data to POST. Remember also to set -T
-u putfile File containing data to PUT. Remember also to set -T
-T content-type Content-type header for POSTing, eg.
‘application/x-www-form-urlencoded’
Default is ‘text/plain’
-v verbosity How much troubleshooting info to print
-w Print out results in HTML tables
-i Use HEAD instead of GET
-x attributes String to insert as table attributes
-y attributes String to insert as tr attributes
-z attributes String to insert as td or th attributes
-C attribute Add cookie, eg. ‘Apache=1234. (repeatable)
-H attribute Add Arbitrary header line, eg. ‘Accept-Encoding: gzip’
Inserted after all normal header lines. (repeatable)
-A attribute Add Basic WWW Authentication, the attributes
are a colon separated username and password.
-P attribute Add Basic Proxy Authentication, the attributes
are a colon separated username and password.
-X proxy:port Proxyserver and port number to use
-V Print version number and exit
-k Use HTTP KeepAlive feature
-d Do not show percentiles served table.
-S Do not show confidence estimators and warnings.
-g filename Output collected data to gnuplot format file.
-e filename Output CSV file with percentages served
-r Don’t exit on socket receive errors.
-h Display usage information (this message)
-Z ciphersuite Specify SSL/TLS cipher suite (See openssl ciphers)
-f protocol Specify SSL/TLS protocol (SSL2, SSL3, TLS1, or ALL)