ORA-00845: MEMORY_TARGET not supported on this system

VM中Oracle的一个测试，原来VM使用内存为4G，后来修改小一些到1G，结果启动报错：
[oracle@asm1 ~]$ sqlplus "/as sysdba"

SQL*Plus: Release 11.2.0.1.0 Production on Tue Oct 4 16:02:10 2011

Copyright (c) 1982, 2009, Oracle.  All rights reserved.

Connected to an idle instance.

SQL> startup
ORA-00845: MEMORY_TARGET not supported on this system

后来修改了/etc/fstab内容：
none                    /dev/shm                tmpfs   defaults,size=6G    0 0
增加size=6G

然后：
shutdown ASM Instance
umount /dev/shm
mount /dev/shm
startup ASM Instance
startup RDBMS Instance就OK了。

具体参照下面文章解决的该问题。

=============================================================
问题：
         利用dbca新建数据库后，关闭数据库，再重启，
         结果出现错误：ORA-00845: MEMORY_TARGET not supported on this system

原因：
         官方文档解释
          Starting with Oracle Database 11g, the Automatic Memory Management feature requires more shared
          memory (/dev/shm)and file descriptors. The size of the shared memory should be at least the greater of
          MEMORY_MAX_TARGET and MEMORY_TARGET for each Oracle instance on the computer. If 
          MEMORY_MAX_TARGET or MEMORY_TARGET is set to a non zero value, and an incorrect size is assigned
          to the shared memory, it will result in an ORA-00845 error at startup.
       
         简单来说就是 MEMORY_MAX_TARGET 的设置不能超过 /dev/shm 的大小：

解决（一）修改shm大小：
1    [oracle@FWDB FWDB]$ df -h | grep shm
2    tmpfs                 2.0G     0  2.0G   0% /dev/shm

马上把它加大：
1    [root@FWDB ~]# cat /etc/fstab | grep tmpfs
2    tmpfs /dev/shm tmpfs   defaults,size=4G 0 0

 现在可以通过重启使这个配置生效，也可以通过重新挂载来修改其大小：
1    [root@FWDB ~]# mount -o remount,size=4G /dev/shm
2    [root@FWDB ~]# df -h | grep shm
3    tmpfs 4.0G     0  4.0G   0% /dev/shm

解决（二）修改MEMORY_TARGET大小
通过修改配置文件initxxxx.ora,修改memory_target的大小，
#vi initxxxx.ora
#sqlplus /nolog
#SQL> startup pfile='/xxx/xxxx/xxx/xxx/xxx/initxxxx.ora';
#SQL> create spfile from pfile;

Ref: http://shanchao7932297.blog.163.com/blog/static/1363624201131443532446/