说明：
ab（ApacheBench）可以用来测试web服务器的执行效率。ab包含在apache安装目录bin目录下。ab可以针对某一特定URL模拟出连续的联机请求，同时还可以仿真出同时间点个数相同的联机请求，因而可以利用ab帮助我们在网站开发期间仿真实际上线可能的情况，利用仿真出来的数据做为调整服务器设定或程序的依据。
参数：ab 用法如下
Usage: ab [options] [http[s]://]hostname[:port]/path
Options are:
-n requests Number of requests to perform //请求次数
-c concurrency Number of multiple requests to make //同一时间发出多少个请求（并行连接）
-t timelimit Seconds to max. wait for responses //等待响应时间
-p postfile File containing data to POST
-T content-type Content-type header for POSTing
-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 //http验证, 分隔传递用户名及密码
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 //查看ab版本
-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
-s Use httpS instead of HTTP (SSL)
-h Display usage information (this message)
实例：
# ab -n 请求数 -c 并发数 测试 url
# ab -n 100 -c 5 -k http://www.gaingreat.com/42.html //必须在后方指定相应文件42.html或加上“/”
This is ApacheBench, Version 2.0.40-dev <$Revision: 1.146 $> apache-2.0
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Copyright 2006 The Apache Software Foundation, http://www.apache.org/
Benchmarking www.gaingreat.com (be patient).....done
Server Software: nginx //Web服务器引擎
Server Hostname: www.gaingreat.com //服务器地址
Server Port: 80 //服务器端口
Document Path: /42.html //请求的文件路径
Document Length: 37927 bytes //文件大小
Concurrency Level: 5 //并发次数
Time taken for tests: 32.732276 seconds //测试所需时间
Complete requests: 100 //成功请求次数
Failed requests: 73 //失败请求次数
(Connect: 0, Length: 73, Exceptions: 0)
Write errors: 0 //写入错误
Keep-Alive requests: 0
Total transferred: 3817232 bytes //测试过程传输字节数
HTML transferred: 3791532 bytes //HTML内容传输字节数
Requests per second: 3.06 [#/sec] (mean) //每秒请求数 ( 平均 )
Time per request: 1636.614 [ms] (mean) //每次并发请求时间 ( 所有并发 )
Time per request: 327.323 [ms] (mean, across all concurrent requests) //每一请求时间 ( 并发平均 )
Transfer rate: 113.86 [Kbytes/sec] received //平均传输速率
Connection Times (ms) //响应时间小、中、大值
min mean[+/-sd] median max
Connect: 16 183 111.5 192 460
Processing: 793 1427 548.2 1296 3839
Waiting: 300 822 485.0 650 3190
Total: 925 1611 512.8 1447 3891
//以下为所有请求的平均速度，如在测试过程中进度到50%时平均响应时间为1447ms，到66%时
平均响应时间为1567ms
Percentage of the requests served within a certain time (ms)
50% 1447
66% 1567
75% 1667
80% 1742
90% 2241
95% 2793
98% 3748
99% 3891
100% 3891 (longest request)
附录：
附录1：关于ab -n 请求数 -c 并发数 测试 url的部分说明
“-n”表示：每次请求数，默认不能超过1024个，否则需要修改系统进程限制。
“-c”表示：1个请求的并发连接数，默认最大不能超过50000。
并发连接数不能够大于请求数，即C≤ N 否则会提示：Cannot use concurrency level greater than total number of requests。
附录2.ab: error while loading shared libraries: libaprutil-1.so.0: cannot open shared object file: No such file or directory
这是因为apr-utils没用安装，centOS的话，直接yum install apr-utils即可。若apr-utils是编译安装的，如我这里的/usr/local/apr-utils目录，刚ln -s /usr/local/apr-util/lib/libaprutil-1.so.0* /usr/lib64/将apr-utils软链接到/usr/lib64目录下(64位系统，32位系统目录为/usr/lib/)
附录3.yum install arp-utils时用到的文件目录
# rpm -ql apr-util /usr/lib64/apr-util-1 /usr/lib64/apr-util-1/apr_dbd_pgsql-1.so /usr/lib64/apr-util-1/apr_dbd_pgsql.so /usr/lib64/apr-util-1/apr_dbd_sqlite3-1.so /usr/lib64/apr-util-1/apr_dbd_sqlite3.so /usr/lib64/libaprutil-1.so.0 /usr/lib64/libaprutil-1.so.0.2.7 /usr/share/doc/apr-util-1.2.7 /usr/share/doc/apr-util-1.2.7/CHANGES /usr/share/doc/apr-util-1.2.7/LICENSE /usr/share/doc/apr-util-1.2.7/NOTICE /usr/lib/apr-util-1 /usr/lib/apr-util-1/apr_dbd_pgsql-1.so /usr/lib/apr-util-1/apr_dbd_pgsql.so /usr/lib/apr-util-1/apr_dbd_sqlite3-1.so /usr/lib/apr-util-1/apr_dbd_sqlite3.so /usr/lib/libaprutil-1.so.0 /usr/lib/libaprutil-1.so.0.2.7 /usr/share/doc/apr-util-1.2.7 /usr/share/doc/apr-util-1.2.7/CHANGES /usr/share/doc/apr-util-1.2.7/LICENSE /usr/share/doc/apr-util-1.2.7/NOTICE