如何让linux/Centos 32位支持大于4G内存

遇到一台CentOS 5.6的机器需要升级内存到6GB, 结果发现系统居然是32位的，于是搜索能否让32位系统支持4G以上内存的方法。

如何让linux/Centos 32位支持8G内存?内核安装PAE支持大于4GB内存的方法。linux/Centos 32bit OS 默认不支持4G以上内存的，安装一个kernel-PAE补丁就可以解决了，操作前最好对虚拟机做一个快照备份，以防出现意外时可以恢复到正常状态。

下面是几个步骤：

[[email protected]]# free
            total       used       free     shared    buffers     cached
Mem:       3881968     637928    3244040          0     111292     461680
-/+ buffers/cache:      64956    3817012
Swap:      4192924          0    4192924
[[email protected]]# yum install kernel-PAE
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
centos-burstnet                                                                                                                                          | 1.1 kB     00:00   
updates-burstnet                                                                                                                                         | 1.9 kB     00:00   
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package kernel-PAE.i686 0:2.6.18-194.32.1.el5 set to be installed
--> Finished Dependency Resolution
Dependencies Resolved
================================================================================================================================================================================
Package                                 Arch                              Version                                          Repository                                     Size
================================================================================================================================================================================
Installing:
kernel-PAE                              i686                              2.6.18-194.32.1.el5                              updates-burstnet                               17 M
Transaction Summary
================================================================================================================================================================================
Install       1 Package(s)
Upgrade       0 Package(s)
Total download size: 17 M
Is this ok [y/N]: y
Downloading Packages:
kernel-PAE-2.6.18-194.32.1.el5.i686.rpm                                                                                                                  |  17 MB     00:01   
Running rpm_check_debug
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
 Installing     : kernel-PAE                                                                                                                                               1/1
Installed:
 kernel-PAE.i686 0:2.6.18-194.32.1.el5                                                                                                                                      
Complete!
[[email protected]]# free
            total       used       free     shared    buffers     cached
Mem:       3881968     637928    3244040          0     111292     461680
-/+ buffers/cache:      64956    3817012
Swap:      4192924          0    4192924
[[email protected]]# vi /boot/grub/grub.conf
default=0    #（把default=1改成default=0）
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title CentOS (2.6.18-194.32.1.el5PAE)    #（有这行PAE的就表示安装pae内核成功）
       root (hd0,0)
       kernel /vmlinuz-2.6.18-194.32.1.el5PAE ro root=LABEL=/
       initrd /initrd-2.6.18-194.32.1.el5PAE.img
title CentOS (2.6.18-194.32.1.el5)
       root (hd0,0)
       kernel /vmlinuz-2.6.18-194.32.1.el5 ro root=LABEL=/
       initrd /initrd-2.6.18-194.32.1.el5.img
title CentOS (2.6.18-194.el5)
       root (hd0,0)
       kernel /vmlinuz-2.6.18-194.el5 ro root=LABEL=/
       initrd /initrd-2.6.18-194.el5.img
[[email protected]]# reboot  （这里重启服务器，祈祷吧，有时候主板或网卡不支持，那么就只能联系机房了）
Broadcast message from root (pts/0) (Thu May 19 18:52:34 2011):
The system is going down for reboot NOW!
[[email protected]]# free
            total       used       free     shared    buffers     cached
Mem:       8295488     215248    8080240          0      19460     142592
-/+ buffers/cache:      53196    8242292
Swap:      4192924          0    4192924

升级完成，可以支持大内存了。