Linux HTTP Load Testing with httperf

Linux logohttperf is an easy-to-use but powerful GPL2 command line (CLI) stress and load testing tool for linux.

Installing httperf

CentOS 6:

yum install httperf

CentOS 7:

rpm -Uvh rpmforge-release-0.5.3-1.el7.rf.x86_64.rpm
yum install httperf

Running httperf

  1. Always get permission from the site owner first before doing load testing
  2. It’s important to start by calibrating your tool first. Send one request and check the response:
$ httperf --server --uri /index.php --print-request --print-reply -d10

If you see non-200 HTTP responses, like this 301 example response below, then you need to ensure you have the correct –uri parameter:

httperf: warning: open file limit > FD_SETSIZE; limiting max. # of open files to FD_SETSIZE
httperf: maximum number of open descriptors = 1024
SH0:GET /index.php HTTP/1.1
SH0:User-Agent: httperf/0.9.0
SS0: header 83 content 0
RH0:HTTP/1.1 301 Moved Permanently

You can ignore the open files warning – it’s a bug in httperf. Just keep the load under 200 connections, or compile your own version from source.

Now we’re ready to do concurrent testing:

$ httperf --server --uri /index.php --num-conn 20 --num-cal 10 --rate 2 --timeout 5
httperf --timeout=5 --client=0/1 --port=80 --uri=/blog --rate=2 --send-buffer=4096 --recv-buffer=16384 --num-conns=20 --num-calls=10
httperf: warning: open file limit > FD_SETSIZE; limiting max. # of open files to FD_SETSIZE
Maximum connect burst length: 1

Total: connections 20 requests 200 replies 200 test-duration 10.675 s

Connection rate: 1.9 conn/s (533.8 ms/conn, <=4 concurrent connections)
Connection time [ms]: min 1175.2 avg 1266.2 max 1728.3 median 1179.5 stddev 179.3
Connection time [ms]: connect 63.4
Connection length [replies/conn]: 10.000

Request rate: 18.7 req/s (53.4 ms/req)
Request size [B]: 73.0

Reply rate [replies/s]: min 18.2 avg 19.1 max 20.0 stddev 1.3 (2 samples)
Reply time [ms]: response 120.3 transfer 0.0
Reply size [B]: header 238.0 content 0.0 footer 0.0 (total 238.0)
Reply status: 1xx=0 2xx=0 3xx=200 4xx=0 5xx=0

CPU time [s]: user 2.36 system 8.30 (user 22.1% system 77.7% total 99.9%)
Net I/O: 5.7 KB/s (0.0*10^6 bps)

Errors: total 0 client-timo 0 socket-timo 0 connrefused 0 connreset 0
Errors: fd-unavail 0 addrunavail 0 ftab-full 0 other 0

Always check for non-zero error counts.

Going Pro

After you're comfortable using httperf, here's how to take it to the next level:

  1. use a dedicated physical machine separate from your subject under test to reduce intrusive latencies, and tail the server logs in separate terminal windows. Graph CPU and RAM consumption of the subject.
  2. build your own version of httperf with your preferred options. On CentOS 7:
    git clone
    cd httperf
    # read
    sudo yum install automake openssl-devel libtool
    libtoolize --force
    autoreconf -i
    sudo make install
    read the links below and configure open files, port range and TCP timeout
  3. do runs 3 times at different times of the day and/or seasons
  4. again, always check for non-zero error counts
  5. add load and stress testing to your server and application deployment checklists. There's always some kind of surprise just waiting to be discovered. :)
Advanced Notes
  1. test tools are one of those things where you really need the source code to get what you want
  2. Runnning strace httperf ..., we see that httperf does polling with the select() system call. Hmm ...
    select(4, [3], [], NULL, {0, 0})        = 0 (Timeout)
    select(4, [3], [], NULL, {0, 0})        = 0 (Timeout)
    select(4, [3], [], NULL, {0, 0})        = 0 (Timeout)
    [..] stress test your web server with httperf
SO: Changing the file descriptor size in httperf Increase "Open Files Limit" The USE Method

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