Insight on shmax/shmall and /dev/shm settings for oracle on Linux

1) /dev/shm---- this is used by oracle when we want to use AMM(Automatic memory management).... this needs to be set to a value equal to the memory_target of all the databases on the system.
this is not used if we are not using AMM for Oracle..

df -h

2) shmall(/etc/sysctl.conf)  -----his should be set in pages. this value should be equal to the sum of all the Databases on that machine/system(all sga's/preferrably memory_target that we want to use/set) in pages.... to get this value.... first find the page-size value...

getconf PAGE_SIZE....


3) shmax(/etc/sysctl.conf)  ---- is set here...

while starting a database if you see the below errors.... check the parameter setting on the OS..

ORA-27102: out of memory
no space left on device...

SHMAX should be equal to or more than the SGA's/memory of all the databases on that system. mostly, we need the SHMAX should be more than memory_target for a database ..


Hope this helps....