Sometimes, the kernel does not recognize all of your memory (RAM). You can check this with the cat /proc/meminfo command.
Verify that the displayed quantity is the same as the known amount of RAM in your system. If they are not equal, add the following line to the /boot/grub/grub.conf:
Replace xx with the amount of RAM you have in megabytes.
In /boot/grub/grub.conf, the above example would look similar to the following:
#NOTICE: You have a /boot partition. This means that# all kernel paths are relative to /boot/default=0timeout=30splashimage=(hd0,0)/grub/splash.xpm.gztitle Linux (2.6.9-1.641_EL) root (hd0,0) kernel /vmlinuz-2.6.9-1.641_EL ro root=/dev/hda3 mem=128M
Once you reboot, the changes made to grub.conf are reflected on your system.
Once you have loaded the GRUB boot screen, type e for edit. 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.
At the end of the kernel line, add
where xx equals the amount of RAM in your system.
Press [Enter] to exit edit mode.
Once the boot loader screen has returned, type b to boot the system.
Itanium users must enter boot commands with elilo followed by the boot command.
Remember to replace xx with the amount of RAM in your system. Press [Enter] to boot.
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