The Linux Page

Testing your memory on a live Linux system

Today I wanted to test the memory on a remote server. I could not just reboot and run memtest86+ so instead I had to look for a different solution to testing most of the computer memory without having to reboot...

I found an interesting page in that regard describing a way to do so using md5sum on a very large file.

The is a verbatim copy of the Linux command line proposed.

  dd if=/dev/urandom bs=768304 of=/tmp/memtest count=1050
   md5sum /tmp/memtest; md5sum /tmp/memtest; md5sum /tmp/memtest

The size, 768304 is expected to be close to your memory size. You should know how much memory you have, otherwise you can type free or top and you'll see somewhere what it is.

The count parameter shows how many times the bs size will be duplicated. I think that there is a little mistake in that the count should be 1024 instead. Possibly also the numbers should be inverted. The default bs is 512 which is the size of a block and the count should be how many times you repeat that block.

  dd if=/dev/urandom bs=1024 of=/tmp/memtest count=768304

This means write 768304 blocks of 1024 bytes in /tmp/memtest using random data as provided by /dev/urandom.

The second line runs md5sum 3 times on that file. Since Linux has the bad habit of caching the data, this means a lot of that data will reside in memory when the 2nd and 3rd md5sum are run. And that means you're testing a great deal of the memory of your computer.

The idea is that if the memory is going bad, then the each md5sum will return a different result and you are likely to get ECC errors in your console and in your syslog file (if such are turned on in your BIOS and kernel.)

Now, if you can, try your memory with memtest86+. It's really hard on the RAM, not so much on modern processors.

Original post http://www.cyberciti.biz/tips/howto-linux-server-memory-check.html

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