使用虚拟机时，机器实在太卡，原来虚拟机会把你所分配给它的内存扣死，昨天把虚拟机的内存从1.5G缩小到1G。机器果然顺畅了，不过担心的问题也出现了－－oracle的实例启动不了。
SQL> startup
ORA-00845: MEMORY_TARGET not supported on this system

来自Oracle的官方解析是：
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
我不知道怎样调整MEMORY_MAX_TARGET，所以就调整/dev/shm的大小

查看原本大小
[root@Shine2 oracle]# df -h|grep shm
tmpfs                 505M  75K  505M  1% /dev/shm

在文件搜索里找到6个initXXX.ora文件，随便打开两个发现memorytarget的值不同。。。
其中有一个是1G，那就1G吧。。。也不知道是什么
[oracle@Shine2 ~]$ gedit /etc/fstab
把文件中
tmpfs                   /dev/shm                tmpfs  defaults        0 0
改为
tmpfs                   /dev/shm                tmpfs  defaults,size=1G        0 0

[root@Shine2 oracle]# umount /dev/shm
出现错误：/dev/shm is busying，并提示我使用lsof命令。

lsof（list open files）是一个列出当前系统打开文件的工具。

[root@Shine2 oracle]# lsof |grep shm
lsof: WARNING: can't stat() fuse.gvfs-fuse-daemon file system /home/oracle/.gvfs
      Output information may be incomplete.
pulseaudi 2997    oracle  mem       REG       0,16  67108904       9562 /dev/shm

[root@Shine2 oracle]# kill 2997
[root@Shine2 oracle]# lsof |grep shm
lsof: WARNING: can't stat() fuse.gvfs-fuse-daemon file system /home/oracle/.gvfs
      Output information may be incomplete.
把使用该文件的进程干掉了

[root@Shine2 oracle]# umount /dev/shm
[root@Shine2 oracle]# mount /dev/shm
[root@Shine2 oracle]# df -h|grep shm
tmpfs                 1.0G  400M  625M  40% /dev/shm
卸载再重新挂载后，实例终于可以启动了～哈哈<img type="face" src="http://www.sinaimg.cn/uc/myshow/blog/misc/gif/E___6708EN00SIGG.gif" real_src="http://www.sinaimg.cn/uc/myshow/blog/misc/gif/E___6708EN00SIGG.gif" alt="ORA-00845: MEMORY_TARGET not supported on this system" title="ORA-00845: MEMORY_TARGET not supported on this system" style="margin:0px;padding:0px;list-style:none;" />

[oracle@Shine2 ~]$ sqlplus

SQL*Plus: Release 11.2.0.1.0 Production on Sat Jul 30 09:34:01 2011

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

Enter user-name: / as sysdba
Connected to an idle instance.

SQL> startup
ORACLE instance started.

Total System Global Area  640286720 bytes
Fixed Size            1338420 bytes
Variable Size          461374412 bytes
Database Buffers      171966464 bytes
Redo Buffers            5607424 bytes
Database mounted.
Database opened.