Stress Testing A Linux Box

Using Fedora's Stress Command

To stress test the machine, we should install the stress command.

Login as root

If the compile tools are not installed then install them:
yum install gcc gcc-c++ autoconf automake Then install the command itself: wget http://pkgs.fedoraproject.org/repo/pkgs/stress/stress1.0.4.tar.gz/a607afa695a511765b40993a64c6e2f4/stress-1.0.4.tar.gz
tar zxvf stress-1.0.4.tar.gz
cd stress-1.0.4
./configure
make
make install
To do the stress tests themselves:

Stress CPU for 10 minutes: stress –c 5 –t 1200s Stress Memory for 10 minutes stress –m 10 –t 1200s Stress disk io for 10 minutes stress –d 10 –t 1200s The first command will push CPU to 500%. It only works on one core, so it may need to run several time simultaneously, depending on how many cores there are. The second command produces 10 spinning process, and the third 10 spinning disk write processes.

The commands can be combined (-c 5 –m 10 –d 10 –t 1200s).

Using A Script

But what if the system is locked down and the stress command cannot be installed? It is possible to perform the stress test using scripting instead. The following scripts do the job.

This script should hammer the CPU load. It runs a huge number of awk calculations as several background processes
#!/bin/bash
if [ $1 ]; then
        NUM_PROC=$1
else
        NUM_PROC=10
fi

uptime

for i in $(seq 1 $NUM_PROC ); do
   awk 'BEGIN {for(i=0;i<10000;i++)for(j=0;j<10000;j++);}' &
   pidarr[$i]=$!
   echo ${pidarr[$i]}
done

ps -fp "${pidarr[*]}"

uptime
We can use dd and a variation of the above script to thrash the disk IO:
#!/bin/bash
if [ $1 ]; then
        NUM_PROC=$1
else
        NUM_PROC=10
fi

for i in $(seq 1 $NUM_PROC ); do
   dd if=/dev/sda of=/dev/null &
   pidarr[$i]=$!
   echo ${pidarr[$i]}
done

ps -fp "${pidarr[*]}"
And for memory, we can use another variation:
#!/bin/bash
if [ $1 ]; then
        NUM_PROC=$1
else
        NUM_PROC=2
fi

BS=$(free | grep "^Mem" | awk '{print $2}' | head -1)

for i in $(seq 1 $NUM_PROC ); do
   dd if=/dev/urandom bs=$BS of=/dev/null count=1050 &
   pidarr[$i]=$!
   echo ${pidarr[$i]}
done

ps -fp "${pidarr[*]}"
This caches huge blocks of random numbers (using a block size of the total amount of used space in the system). Doing it a couple of times simultaneously will do the trick.

Windows New Lines Cause \r Scripting Errors

Using notepad++ to write Linux or Unix shellscripts creates scripts where each line ends in Windows format <line feed><carriage return> rather than Unix format <carriage return> new lines.

This will typically throw up an error when trying to run a script, for example:

$ ./dbusers.sh -s UC1 -rUC2 user1 user2 user3
./dbusers.sh: line 33: $'\r': command not found
./dbusers.sh: line 36: syntax error near unexpected token `$'in\r''
'/dbusers.sh: line 36: `   case $value in

This can be fixed in notepad++ in the Settings menu:

Settings / Preferences / New Document and change the Format (Line ending) to Unix/OSX.

This only applies to new documents, so close any shell scripts which are open for editing in Notepad, then convert them in Linux to get rid of the extra line feeds. This can be done either using a sed command, or the dos2unix command. Not every distribution has the dos2unix command but sed is universal.

sed -i 's/\r\n/\n/g' <script>

This simple sed command searches for <linefeed><carriage return> (\r\n) and replaces it with a simple <carriage return> (\n).

The script can now be loaded back into notepad++ where it will work correctly.