During the manual creation of an Oracle 11g Release 2 database, you may sometimes encounter the ORA 00845 error when running the CREATE DATABASE command from SQLPlus, on the Red Hat Linux platform.
This error is caused by an insufficiently sized /dev/shm device on the server, which doesn’t at least correspond to the actual amount of physical memory (RAM) installed. In Linux, the /dev/shm device is not a conventional filesystem, but is actually a means of efficiently sharing and utilizing shared virtual memory on the Linux operating system.
An application/program can allow processes (that are permitted) to access memory portions created on this /dev/shm device. In practical terms, in order for Oracle to use Automatic Memory Management (AMM) on Linux, this device needs to be first adequately sized, or this error will be encountered when trying to start the Oracle instance.
To solve this issue (for example on a server that has 2Gb of physical memory allocated to the 11g Oracle database), you can issue the following as the ROOT user:
mount -t tmpfs shmfs -o size=2g /dev/shm
To make this permanent, the following entry can be added to the /etc/fstab file:
shmfs /dev/shm tmpfs size=2g 0
oracletempspace (or my adventures with Oracle) 
ya.. it worked.. thnx alot