ORA-00845 When Starting Up An 11g Instance

Today when i trying to connect 11g (newly installed software) and trying to startup 11g database then got below error message

SQL> STARTUP
ORA-00845: MEMORY_TARGET not supported on this system

Reason:

This feature requires the /dev/shm file system to be mounted for at least %llu bytes.
/dev/shm is either not mounted or is mounted with available space less than this size.

Explanation:

AMM (Automatic Memory Management) is a new feature in 11 which manages both SGA and PGA.

MEMORY_TARGET is used instead of SGA_TARGET and MEMORY_MAX_TARGET is used instead of SGA_MAX_SIZE (defaults to MEMORY_TARGET ).

It uses /dev/shm on Linux. If max_target set over /dev/shm size, you get the error messages.

Solution:

1. If you are installing Oracle 11g on a Linux system, note that Memory Size (SGA and PGA), which sets
the initialization parameter MEMORY_TARGET or MEMORY_MAX_TARGET, cannot be greater than the shared memory filesystem (/dev/shm) on your operating system. To resolve the current error, increase the /dev/shm file size. For example:
# mount -t tmpfs shmfs -o size=7g /dev/shm
Also, to make this change persistent across system restarts, add an entry in /etc/fstab similar to the following:

shmfs /dev/shm tmpfs size=7g 0
2. This error may also occur if /dev/shm is not properly mounted. Make sure your df output is similar to the following:

$ df -k
Filesystem 1K-blocks Used Available Use% Mounted on
...
shmfs 6291456 832356 5459100 14% /dev/shm
3. If configuring AMM is not possible due to lack of space on /dev/shm mount point, you can configure ASMM instead of AMM, i.e. set SGA_TARGET, SGA_MAX_SIZE and PGA_AGGREGATE_TARGET instead of MEMORY_TARGET.

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