ORA-27125:unable to create shared memory segment

环境：OEL6.3  64位，Oracle10.2.0.1 64

问题：DBCA创建库时遇到ORA-27125:unable to create shared memory segment

解决方法

[root@o10gos dbs]# id oracle

uid=54321(oracle) gid=54321(oinstall) groups=54321(oinstall),54322(dba)

在此再验证：

[root@o10gos dbs]# cat /etc/group


[root@o10gos dbs]# echo "54322" >/proc/sys/vm/hugetlb_shm_group 
[root@o10gos dbs]# 


解决办法来自：
http://hi.baidu.com/lengths/item/cde8a52406db09f850fd875d



关于hugetlb_shm_group，衣钩大师早有分析：

http://www.eygle.com/archives/2011/12/hugepageshugetl.html

那么hugetlb_shm_group组是什么呢？以下是解释：
hugetlb_shm_group contains group id that is allowed to create SysV shared memory segment using hugetlb page

这里反复提到了HugePage，以下是关于HugePage的说明和解释：

When a process uses some memory, the CPU is marking the RAM as used by that process. For efficiency, the CPU allocate RAM by chunks of 4K bytes (it's the default value on many platforms). Those chunks are named pages. Those pages can be swapped to disk, etc.

Since the process address space are virtual, the CPU and the operating system have to remember which page belong to which process, and where it is stored. Obviously, the more pages you have, the more time it takes to find where the memory is mapped. When a process uses 1GB of memory, that's 262144 entries to look up (1GB / 4K). If one Page Table Entry consume 8bytes, that's 2MB (262144 * 8) to look-up.

Most current CPU architectures support bigger pages (so the CPU/OS have less entries to look-up), those are named Huge pages (on Linux), Super Pages (on BSD) or Large Pages (on Windows), but it all the same thing. 

另在安装过程中遇到的操作系统验证错误，可以通过如下方式解决：
在Linux系统中安装oralce的过程中，如果Linux发行版本不是oracle的推荐版本，可能会报如下错误，导致runInstaller无法完成：
Checking operating system version: must be redhat-3, SuSE-9, redhat-4, UnitedLinux-1.0, asianux-1 or asianux-2
Failed <<<<

遇到这个问题，可以通过如下三种方式解决

1、修改Linux的发行标记

如在redhat-5上安装oracle的时候，需要将文件 '/etc/redhat-release'的内容由
Red Hat Enterprise Linux Server release 5 (Tikanga)

修改为Oracle支持的版本
Red Hat Enterprise Linux Server release 4 (Tikanga)

2、runInstaller的时候加上-ignoreSysPreReqs参数，如：
./runInstaller -ignoreSysPreReqs

3.修改oraparam.ini的参数
增加你的系统版本号