RHEL5关于大内存的问题
安装RHEL 5，硬件为4G内存，安装完成后显示为 3.2G
原因，没有安装 kernel-PAE-2.6.18-8.el5.i686.rpm软件包。
RHEL 5的文档中关于内核的说明：
Red Hat Enterprise Linux contains the following kernel packages
kernel:Contains the kernel for multi-processor systems.For x86 system,only the first 4GB of RAM is used.As such,x86systems with over 4GBof RAM should use the kernel-PAE.
kernel-devel:Contains the kernel headers and makefiles sufficient to bulid modules against the kernel package.
kernel-PAE(only for i686systems):This package offers the following key configuration options (in addition to the options already enabled for the kernel package)
1.Support for over 4GB of RAM (up to 64GB for the x86)
2.PAE(Physical Address Extension)or 3-level paging on x86 processors that support PAE
3.4GB/4GB split:4GB of virtual address space for the kernel an almost 4GB for each userprocess on x86systtems
另外还有以下内核：kernel-PAE-devel,kernel-doc,kernel-headers,kernel-xen,kernel-xen-devel.
解决：
主要需要2个方面设置
1.bios:在bios里开启对大内存的设置
2.安装支持大内存的kernel
安装kernel-PAE-2.6.18-8.el5.i686.rpm
rpm -ivh kernel-PAE-2.6.18-8.el5.i686.rpm
安装完后，
vi /etc/grub.conf
如果看到如下代码 代表PAE内核已经安装好了
title Red Hat Enterprise Linux Server (2.6.18-8.el5PAE)
root (hd0,0)
kernel /vmlinuz-2.6.18-8.el5PAE ro root=LABEL=/ rhgb quiet
initrd /initrd-2.6.18-8.el5PAE.img
修改启动顺序，将default=1改为default=0即可