CentOS 5 32-bit only recognize maximum 3 GB RAM

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I have an old CentOS 5 32-bit server. This is a VPS. I recently purchased additional RAM for my VPS and now total RAM is 4 GB but when I run free -m via SSH, it is showing only 3 GB RAM. I can’t use 1 GB unallocated RAM. Is there any RAM limitation in CentOS 5 32-bit?


By default CentOS 5 32-bit Kernel will only use first 3 GB RAM even if you allocate 4 GB RAM. You will a Kernel with PAE (Physical Address Extension) support. You can install it using the following command:

yum install kernel-PAE

You will have to reboot your VPS after installing PAE support Kernel. You may need to change grub.conf to boot your VPS automatically from new Kernel.

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