【问题记录】数据库打不开 报ORA-00845错误 /dev/shm设置过小
--startup时报错
SQL> startup
ORA-00845: MEMORY_TARGET not supported on this system
--查看该错
[oracle11@CD1 goldengate]$ oerr ora 845
00845, 00000,"MEMORY_TARGET not supported on this system"
// *Cause: TheMEMORY_TARGET parameter was not supported on this operating system or /dev/shmwas not sized correctly on Linux.
// *Action:Refer to documentation for a list of supported operating systems. Or,size /dev/shm to be at least the SGA_MAX_SIZE oneach Oracle instance running on the system
在oracle 11g中新增的内存自动管理的参数MEMORY_TARGET，它能自动调整SGA和PGA，这个特性需要用到/dev/shm共享文件系统，而且要求/dev/shm必须大于MEMORY_TARGET（SGA_MAX_SIZE），如果/dev/shm比MEMORY_TARGET小就会报错。
--查看当前/dev/shm大小
[oracle11@CD1 goldengate]$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
26G 16G 8.6G 65% /
/dev/sda1 99M 13M 82M 14% /boot
tmpfs 624M 0 624M 0% /dev/shm
--将/dev/shm调大
[root@CD1 ~]# cat /etc/fstab | grep tmpfs
tmpfs /dev/shm tmpfs defaults 0 0
[root@CD1 ~]# mount -o remount,size=1g /dev/shm
--确保操作系统重启之后能生效，修改/etc/fstab文件
[root@CD1 ~]# cat /etc/fstab | grep tmpfs
tmpfs /dev/shm tmpfs defaults 0 0
[root@CD1 ~]# vi /etc/fstab
/dev/VolGroup00/LogVol00/ ext3 defaults 1 1
LABEL=/boot /boot ext3 defaults 1 2
tmpfs /dev/shm tmpfs defaults,size=1g 0 0
devpts /dev/pts devpts gid=5,mode=620 0 0
sysfs /sys sysfs defaults 0 0
proc /proc proc defaults 0 0
/dev/VolGroup00/LogVol01swap swap defaults 0 0
--确认修改结果
[root@CD1 ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
26G 16G 8.6G 65% /
/dev/sda1 99M 13M 82M 14% /boot
tmpfs 1.0G 0 1.0G 0% /dev/shm
--打开数据库
[root@CD1 ~]# su - oracle11
[oracle11@CD1 ~]$ sql
SQL*Plus:Release 11.2.0.3.0 Production on Wed Dec 25 13:18:48 2013
Copyright (c)1982, 2011, Oracle. All rights reserved.
Connected toan idle instance.
SQL> startup
ORACLEinstance started.
Total SystemGlobal Area 839282688 bytes
FixedSize 2233000 bytes
VariableSize 511708504 bytes
DatabaseBuffers 318767104 bytes
RedoBuffers 6574080 bytes
Databasemounted.
Databaseopened.
成功打开了！
--查看memory_target参数
SQL> show parameter memory_target
NAME TYPE VALUE
--------------------------------------------------------------------- ------------------------------
memory_target big integer 804M
SQL> show parameter SGA_MAX_SIZE
NAME TYPE VALUE
--------------------------------------------------------------------- ------------------------------
sga_max_size big integer 804M
原先的/dev/shm 为624M，小于804M，因此数据库不能打开！