After I had increased the memory in my server from 2 GB to 4 GB, I found my server could see the memory about 3.5 GB only. I found this problem happened from my Kernel didn’t support so I would like to upgrade the Kernel so as to use my memory at 4 GB.
And these are steps for solve this problem.
1. Upgrade the Kernel.
# yum install kernel-PAE
2. If you would like to compile some software such as VMWare, you should install kernel-PAE-devel too. (Optional)
# yum install kernel-PAE-devel
3. Change DEFAULTKERNEL=kernel-PAE in file /etc/sysconfig/kernel such as
# UPDATEDEFAULT specifies if new-kernel-pkg should make # new kernels the default UPDATEDEFAULT=yes # DEFAULTKERNEL specifies the default kernel package type DEFAULTKERNEL=kernel-PAE