Startup failure ORA-00845: MEMORY_TARGET not supported on this system

startup of database was failing with the below error
ORA-00845: MEMORY_TARGET not supported on this system

There are two ways to resolve this issue.
1. Decrease memory_target. Good in causal usage of DB
2. Increase in /dev/shm

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

MEMORY_TARGET parameter is stored in pfile & spfile at $ORACLE_HOME/dbs

cd $ORACLE_HOME/dbs


create pfile at a temporary location as spfile can not be read.

SQL> create pfile='/tmp/initKSKDB.ora' from spfile;

File created.


in the temporary pfile, we could see MEMORY_TARGET as 8G
*.memory_target=8589934592

we reduced to 2G in temporary pfile
memory_target=2G


took the backup of spfile before changing the current spfile

create spfile from pfile='/tmp/initKSKDB.ora';

then started the database as below
SQL> startup nomount
ORACLE instance started.

Total System Global Area 2137886720 bytes
Fixed Size                  2230072 bytes
Variable Size            1275070664 bytes
Database Buffers          838860800 bytes
Redo Buffers               21725184 bytes
SQL>


refer the below for more information on startup of database

http://dbakumar.blogspot.sg/p/for-1st-time-database-users-how-to.html


the other option is to increase /dev/shm

Check the free memory available on server by any of the belwo commands
free -m
free -g
egrep --color 'Mem|Cache|Swap' /proc/meminfo

The configuration works roughly like that:
(run as root):

# umount tmpfs

# mount -t tmpfs shmfs -o size=8000m /dev/shm

df -h /dev/shm
Filesystem            Size  Used Avail Use% Mounted on
shmfs                 7.9G     0  7.9G   0% /dev/shm