I have installed ubuntu 14.04 LTS version. It logs in correctly. However, I have found a flood of printk messages when I logout/shutdown the computer. See the error in the image:

I have used the solution suggested in another question.
i.e., modify sysctl.conf file by UN-commenting kernel.printk = 3 4 1 3. But the system does not allow me to modify sysctl.conf.
I have used the techniques suggested in
https://www.youtube.com/watch?v=i2mDGq5KqpA
as well as this website
Both of them fail to modify the files.
Please note that I am using samsung ssd Pro drive and Dell desktop computer with default BIOS setup.