oracle11g数据库在执行dbca或者调整sga后重启oracle的时候可能会出现:

ORA-00845 MEMORY_TARGET not supported on this system究其原因就是Linux系统的shm的大小比SGA设置的小，造成的。

具体说，SGA设置4G，而shm可能只有1G，网上提供两种解决办法：

01、调整sga的大小，这个明显不是我们所希望的

02、调整shm的大小，这样相对简单，具体操作如下vim /etc/fstab

tmpfs /dev/shm tmpfs defaults 0 0

修改为：

tmpfs /dev/shm tmpfs defaults,size=6G 0 0

重新mount下shm使其生效mount -o remount /dev/shm

通过df可以查看下，没有问题就可以继续安装数据库或者启动数据库了！

说明：服务器上有两个不同数据库实例，启动一个实例的时候没问题。在启动第二个INSTANCE的时候报ORA-00845错误。该测试服务器仅8G内存。 tmpfs 默认是4G

4.0G  1.6G  2.4G  40% /dev/shm.

两个实例的使用内存应该超过了4G，所以修改tmpfs，问题解决了。

但是新问题tmpfs 大小的限制如何确定呢？观察一下内存使用在说吧[oracle@BJRMANTS ~]$ su - root

Password:

[root@BJRMANTS ~]# vim /etc/fstab

[root@BJRMANTS ~]# df -h

Filesystem Size Used Avail Use% Mounted on

/dev/sda2 20G5.8G13G31%/

tmpfs 4.0G 1.6G2.4G40%/dev/shm

/dev/sda1 485M51M409M12%/boot

/dev/sda6 197G160G28G86%/orabak

/dev/sda8 20G6.2G13G34%/oracle

/dev/sda5 690G549G106G84%/oradata

/dev/sda7 187G75G104G42%/oralog

[root@BJRMANTS ~]# mount -o remount /dev/shm

[root@BJRMANTS ~]# df -h

Filesystem Size Used Avail Use% Mounted on

/dev/sda2 20G5.8G13G31%/

tmpfs 6.0G 1.6G4.5G26%/dev/shm

/dev/sda1 485M51M409M12%/boot

/dev/sda6 197G160G28G86%/orabak

/dev/sda8 20G6.2G13G34%/oracle

/dev/sda5 690G549G106G84%/oradata

/dev/sda7 187G75G104G42%/oralog

[oracle@BJRMANTS ~]$ export ORACLE_SID=oelncbi

[oracle@BJRMANTS ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on Wed Dec 510:48:512012

Copyright (c) 1982, 2011, Oracle. All rights reserved.

Connected to an idle instance.

SQL> startup;

ORA-00845: MEMORY_TARGET not supported on this system

SQL>exit

Disconnected

[oracle@BJRMANTS ~]$ export ORACLE_SID=oeldzdz

[oracle@BJRMANTS ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on Wed Dec 510:49:332012

Copyright (c) 1982, 2011, Oracle. All rights reserved.

Connected to:

Oracle Database 11g Enterprise Edition Release 11.2.0.3.0-64bit Production

With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> shutdown abort;

ORACLE instance shut down.

SQL>exit

Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.3.0-64bit Production

With the Partitioning, OLAP, Data Mining and Real Application Testing options

[oracle@BJRMANTS ~]$ export ORACLE_SID=oelncbi

[oracle@BJRMANTS ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on Wed Dec 510:49:512012

Copyright (c) 1982, 2011, Oracle. All rights reserved.

Connected to an idle instance.

SQL> startup;

ORACLE instance started.

Total System Global Area 814227456 bytes

Fixed Size 2232760 bytes

Variable Size 452988488 bytes

Database Buffers 352321536 bytes

Redo Buffers 6684672 bytes

Database mounted.

Database opened.

SQL>exit

Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.3.0-64bit Production

With the Partitioning, OLAP, Data Mining and Real Application Testing options

[oracle@BJRMANTS ~]$ export ORACLE_SID=oeldzdz

[oracle@BJRMANTS ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on Wed Dec 510:54:152012

Copyright (c) 1982, 2011, Oracle. All rights reserved.

Connected to an idle instance.

SQL> startup;

ORACLE instance started.

Total System Global Area 2805977088 bytes

Fixed Size 2231672 bytes

Variable Size 603980424 bytes

Database Buffers 2181038080 bytes

Redo Buffers 18726912 bytes

Database mounted.

Database opened.