➜  ~ ab
ab: wrong number of arguments
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 at a time
    -t timelimit    Seconds to max. to spend on benchmarking
                    This implies -n 50000
    -s timeout      Seconds to max. wait for each response
                    Default is 30 seconds
    -b windowsize   Size of TCP send/receive buffer, in bytes
    -B address      Address to bind to when making outgoing connections
    -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 to use for POST/PUT data, 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.
    -q              Do not show progress when doing more than 150 requests
    -l              Accept variable document length (use this for dynamic pages)
    -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.
    -m method       Method name
    -h              Display usage information (this message)
    -Z ciphersuite  Specify SSL/TLS cipher suite (See openssl ciphers)
    -f protocol     Specify SSL/TLS protocol
                    (TLS1, TLS1.1, TLS1.2 or ALL)
➜  ~ 

➜  ~  ab -c 10 -n 100 http://www.linux.cn/ 
This is ApacheBench, Version 2.3 <$Revision: 1706008 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking www.linux.cn (be patient).....done


Server Software:        nginx
Server Hostname:        www.linux.cn
Server Port:            80

Document Path:          /
Document Length:        178 bytes

Concurrency Level:      10
Time taken for tests:   0.861 seconds
Complete requests:      100
Failed requests:        0
Non-2xx responses:      100
Total transferred:      35800 bytes
HTML transferred:       17800 bytes
Requests per second:    116.09 [#/sec] (mean)
Time per request:       86.142 [ms] (mean)
Time per request:       8.614 [ms] (mean, across all concurrent requests)
Transfer rate:          40.59 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:       32   41   7.3     37      53
Processing:    33   42   7.4     38      55
Waiting:       33   42   7.4     38      55
Total:         65   83  14.7     75     108

Percentage of the requests served within a certain time (ms)
  50%     75
  66%     78
  75%    102
  80%    103
  90%    105
  95%    106
  98%    107
  99%    108
 100%    108 (longest request)