问题描述：巡检时发现某一个节点数据库down了，通过sqlplus 进行系统时显示连接的是一个空实例，尝试通过startup重启数据库报错，提示MEMORY_TARGETnot supported on this system，查看告警日志报MEMORY_TARGET失败，要增加/dev/shm大小才可以解决问题

登录数据库时报错信息如下：

[oracle@db01 ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.4.0 Productionon Mon Oct 30 09:26:35 2017

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to an idle instance.

SQL> startup 

ORA-00845: MEMORY_TARGET not supported on this system

后台日志报如下信息：

Starting ORACLE instance (normal)

WARNING: You are trying to use theMEMORY_TARGET feature. This feature requires the /dev/shm file system to bemounted for at least 13522436096 bytes. /dev/shm is either not mounted or ismounted with available space less than this size. Please fix this so that MEMORY_TARGETcan work as expected. Current available is 12203786240 and used is 454021120bytes. Ensure that the mount point is /dev/shm for this directory.

memory_target needs larger /dev/shm

问题分析：

由于Oracle11g中使用的是AMM，当MEMORY_TARGET大于/dev/shm时就提示不支持此系统，从而报错无法启动数据库，由于/dev/shm是通过tmpfs通过大小的，在Linux环境中可以通过修改此大小解决问题

解决方法：

1、  查看当前的tmpfs大小信息

[oracle@i60001~]$ df -h

Filesystem                     Size  Used Avail Use% Mounted on

/dev/mapper/vg_db01-LogVol02  229G  65G  153G  30% /

tmpfs                            12G  434M   12G   4% /dev/shm--此处要修改

/dev/sde1                       485M   40M 420M   9% /boot

/dev/mapper/vg_db01-LogVol00   30G 5.0G   24G  18% /usr

[oracle@i60001~]$ mount -o size=20G -onr_inodes=1000000 -o noatime,nodiratime -o remount /dev/shm

mount: onlyroot can do that

修改tmpfs大小要通过root用户下面操作，切换到root用户

[oracle@i60001~]$ su root

Password:

2、修改tmpfs大小

[root@db01oracle]#  mount -o size=20G -o nr_inodes=1000000 -o noatime,nodiratime-o remount /dev/shm

[root@db01oracle]# df -h

Filesystem                      Size  Used Avail Use% Mounted on

/dev/mapper/vg_db01-LogVol02  229G  65G  153G  30% /

tmpfs                            20G  434M   20G   3% /dev/shm--修改后的大小

/dev/sde1                       485M   40M 420M   9% /boot

/dev/mapper/vg_db01-LogVol00   30G 5.0G   24G  18% /usr

3、修改tmpfs大小后，再登录数据库中重启实例

[oracle@db01~]$ sqlplus / as sysdba

SQL*Plus:Release 11.2.0.4.0 Production on Mon Oct 30 09:42:02 2017

Copyright (c)1982, 2013, Oracle.  All rights reserved.

Connected toan idle instance.

SQL>startup;    

ORACLEinstance started.

Total SystemGlobal Area 1.3462E+10 bytes

Fixed Size              2265984 bytes

Variable Size                7381978240 bytes

DatabaseBuffers        6039797760 bytes

Redo Buffers                 38014976 bytes

Databasemounted.

Database opened.-显示启动成功

--查询当前的数据库实例是否正常

SQL>select open_mode from v$database;

OPEN_MODE

--------------------

READ WRITE