shmmax=1073741824 or 0X40000000
maxdsiz (and maxdsize_64) = 384M or higher
The kernel parameter shmmax controls that maximum size of a single shared memory segment. So, if you need your SGA larger then 1 gig, increase shmmax accordingly. The parameter semmns controls the number of shared memory segments. Increase this value based on the sum of the processes init.ora parameter for all the running databases on your unix machine. You should also allow for about 10 process per database instance for the Oracle background processes.
This was first published in August 2001