[oracle@www dbs]$ sqlplus / as sysdba SQL*Plus: Release 11.2.0.1.0 Production on Wed Mar 6 16:14:39 2013 Copyright (c) 1982, 2009, Oracle. All rights reserved. Connected to an idle instance. SQL> startup ORA-00845: MEMORY_TARGET not supported on this system SQL> MOS: ORA-00845 Raised When Starting Instance [ID 465048.1] Applies to: Oracle Server - Enterprise Edition - Version 11.1.0.6 and later Linux x86 Linux x86-64 Symptoms During the statup of the database instance the following error is raised: SQL> connect sys as sysdba Enter password: Connected to an idle instance. SQL> STARTUP NOMOUNT ORA-00845: MEMORY_TARGET not supported on this system The instance alert file shows: Starting ORACLE instance (normal) WARNING: You are trying to use the MEMORY_TARGET feature. This feature requires the /dev/shm file system to be mounted for at Least bytes.The /dev/shm is either not mounted or is mounted with available space less than this size. Please fix this so that MEMORY_TARGET can work as expected. Current available is and used is bytes.memory_target needs larger /dev/shm Also error messages like ORA-4031 are reported and no new connections can be established in the database. Changes The Automatic Memory Management (AMM) has been implemented by setting parameters like MEMORY_TARGET and/or MEMORY_MAX_TARGET. Cause The new Automatic Memory Management functionality uses /dev/shm on Linux for SGA and PGA management. The errors occur if either MEMORY_TARGET or MEMORY_MAX_TARGET is configured larger than the configured /dev/shm size, or if /dev/shm is mounted incorrectly. Solution Please confirm that ORACLE_HOME is set correctly. This error sometimes happens when it is not set correctly. Make sure that the /dev/shm size is configured large enough, like in: # mount -t tmpfs shmfs -o size=7g /dev/shm In this case, the size of the shared memory device is configured to be 7GB. In order to make the same change persistent across system reboots, add an entry for this to the /etc/fstab mount table, as in: shmfs /dev/shm tmpfs size=7g 0 Note:you should check with your System Administrator what the "best" size for /dev/shm is based on what has been reported in the alert file. ALso, importantly, many best practices now suggest disabling AMM especially in Exa* Engineered boxes that have larger memory capability and can use Huge / Large pages: as these are mutually exclusive and overall performance will be better using Huge pages Make sure that the df output shows the correct /dev/shm configuration when using Oracle on the system: $ df -k Filesystem 1K-blocks Used Available Use% Mounted on ... shmfs 6291456 832356 5459100 14% /dev/shm