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10.4.7. Is Your RAM Not Being Recognized?

Sometimes, the kernel does not recognize all of your memory (RAM). The following procedure will allow you to confirm this and then adjust the kernel if necessary.
  1. Run the cat /proc/meminfo command and verify that the displayed quantity is the same as the known amount of RAM in your system. If they are not equal, you can first make a temporary change to confirm whether editing the kernel will be effective.
  2. Reboot, and once you have loaded the GRUB boot screen, type e for edit.
  3. You are presented with a list of items in the configuration file for the boot label you have selected. Choose the line that starts with kernel and type e to edit this boot entry.
  4. At the end of the kernel line, add
    mem=xxM
    where xx equals the amount of RAM in your system, then press Enter to exit edit mode.
  5. Once the boot loader screen has returned, type b to boot the system.
  6. Run cat /proc/meminfo again. If the known amount of RAM in your system is now displayed, add the following line to the /etc/grub.d/10_linux file to make the change permanent:
    mem=xxM
    Replace xx with the amount of RAM you have in megabytes.
  7. To update the grub.cfg file so that the change will take effect, run the following command with root privileges.
    grub2-mkconfig --output=/boot/grub2/grub.cfg
In 10_linux, the above example would look similar to the following:
default=0 
timeout=30 
splashimage=(hd0,1)/grub/splash.xpm.gz 
menuentry 'Fedora Linux, with Linux 3.1.0-0.rc6.git0.3.fc16.x86_64'
set root=(hd0,1)
linux /vmlinuz-(2.6.32.130.el6.i686 ro root=UUID=04a07c13-e6bf-6d5a-b207-002689545705 mem=8192M
initrd /initrd-(2.6.32.130.el6.i686.img