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ORA-00845 - Which value for /dev/shm is needed to startup database without ORA-00845 (Doc ID 1399209.1)

Last updated on OCTOBER 08, 2020

Applies to:

Oracle Database - Standard Edition - Version and later
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Backup Service - Version N/A and later
Oracle Database Cloud Service - Version N/A and later
Information in this document applies to any platform.


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 must be at least the greater of the MEMORY_MAX_TARGET and MEMORY_TARGET parameters for each Oracle instance on the computer.

If the MEMORY_MAX_TARGET parameter or the MEMORY_TARGET parameter is set to a nonzero value, and an incorrect size is assigned to the shared memory, it results in an ORA-00845 error at startup.

On Linux systems, if the operating system /dev/shm mount size is too small for the Oracle system global area (SGA) and program global area (PGA), then you encounter the following error:

ORA-00845: MEMORY_TARGET not supported on this system.

The cause of this error is an insufficient /dev/shm allocation. The total memory size of the SGA and PGA, which sets the initialization parameter MEMORY_TARGET or MEMORY_MAX_TARGET, cannot be greater than the shared memory file system (/dev/shm) on your operating system.


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