A number of good and mostly free tools are available for testing RAM hardware. However, most of these applications are designed to operate in stand-alone mode that requires shutting down the OS. Still, tare a few ways to run memory integrity checks from inside the operating environment. Here we will look at using dd and memtester.

dd

The idea here is simple: use random input to generate a file equal to the total size of RAM; then run MD5 checksum on the file a few times to see if results match. This method has two drawbacks: it requires disk space and it is slow. The script below will see how much memory your system has; it will then make sure you have sufficient disk space before running dd.

While dd is running in the background, the script will keep you updated about the progress. Once dd has finished, md5sum will be executed three times. Your job is to verify that all three values it produces are identical.

#!/bin/bash
# www.krazyworks.com
# The script will use dd and md5sum to test integrity of your RAM

trap ctrl_c INT

configure() {
        # directory for storing temp files
        output_dir="/esstress"

        # temp output file
        output_file="${output_dir}/dd_memtest.tmp"

        # available space in $output_dir
        output_dir_space=$(df -Pk $output_dir | grep -v Filesystem | awk '{print $4}')

        # maximum percentage of $output_dir space to use
        fs_limit=90

        # total system RAM
        total_mem=$(free | grep 'Mem:' | awk '{print $2}')
        total_mem_m=$(free -m | grep 'Mem:' | awk '{print $2}')

        # file for storing PID
        pidfile="/tmp/dd_memtest.pid"
}

preflight() {
        # check disk space requirements
        if [ ${total_mem} -gt `echo "scale=0;${output_dir_space}/100*${fs_limit}"| bc -l` ]
        then
                echo "Not enough free space in ${output_dir}! Exiting..."
                exit 1
        fi

        if [ -f "${output_file}" ]
        then
                /bin/rm "${output_file}"
        fi
}

md5run() {
        # run three interations of md5 checksum to verify data integrity
        for i in 1 2 3
        do
                md5sum "${output_file}"
        done
}

function ctrl_c() {
        echo "Killing dd"

        if [ -f /tmp/pid1 ]
        then
                kill -9 `cat /tmp/pid1`
                /bin/rm -f /tmp/pid1
        fi

        if [ -f "${output_file}" ]
        then
                /bin/rm -f "${output_file}"
        fi
        exit 1
}

dd_memtest() {
        # run dd to generate the output file from random input
        if [ -f /tmp/pid1 ]
        then
                /bin/rm -f /tmp/pid1
        fi

        (dd if=/dev/urandom bs=${total_mem} of="${output_file}" count=1050 & echo $! > /tmp/pid1)&

        echo "Starting test..."
        sleep 5

        while [ -e /proc/`cat /tmp/pid1` ]
        do
                echo "Written `/bin/ls -lash ${output_file} | awk '{print $1}'` of ${total_mem_m}Mb"
                sleep 10
        done

        md5run
        /bin/rm -f "${output_file}"
        /bin/rm -f /tmp/pid1
}

# RUNTIME

configure
preflight
dd_memtest

Memtester is an open-source utility for testing RAM from inside the OS. Download the source code and untar it; run make; and then run make install. Use the following wrapper script to pre-populate required options based on your system’s free memory. It is important to point out that any memory-locking process is capable of crashing your system. The wrapper script will ensure that memtester does not grab more RAM than you can spare. However, this is not a guarantee of a problem-free run and you should be prepared for the possible need to power-cycle the system in case it locks up.

#!/bin/bash
# www.krazyworks.com
# Download Memtester source code from http://pyropus.ca/software/memtester/
# Gunzip, untar, run "make" and "make install"
#
# This script will run memtester using a percentage of your remaining free
# physical RAM to avoid a system lockup. Still, be prepared for the
# possibility that the system may become unresponsive and may need to be
# power-cycled.

configure() {
        MEMTESTER=/usr/local/bin/memtester      # memtester location
        LOOPS=2                                 # number of memtester runs
        RAMLIM=90                               # percentage of free physical RAM to use for the test
}

memtest() {
        "${MEMTESTER}" $(echo "scale=0;`free | grep 'Mem:' | awk '{print $4}'`/100*${RAMLIM}" | bc -l)K ${LOOPS}
}

# RUNTIME

configure

if [ ! -x "${MEMTESTER}" ]
then
        echo "Memtester executable not found! Exiting..."
        exit 1
else
        memtest
fi