已索引

当启动实例时，可能会发生该错误。

Oracle对该错误说的很清楚：

$ oerr ora 00845
00845, 00000, "MEMORY_TARGET not supported on this system"
// *Cause: The MEMORY_TARGET parameter was not supported on this operating system or /dev/shm was 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 on each Oracle instance running on the system.

总结为两个原因：
1.MEMORY_TARGET参数太大，实际剩余内存不能满足该参数值
2.如果剩余内存远大于参数值，还是报该错误，则多是/dev/shm的问题，这种情况多发生在生产物理内存扩容，加大MEMORY_TARGET参数后。

$ df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1              967G   22G  896G   3% /
/dev/sda2              99M   12M   82M  13% /boot
tmpfs                1014M  264M  750M  27% /dev/shm

可以在/etc/fstab中通过defaults,size=2G来修改该大小，然后原子remount即可。