ORA-00845: MEMORY_TARGET not supported on this system

It is a very common issue that we always encounter while installing or starting database.You have started your listener and now when you are trying to start your database it comes up with errors

SQL> connect / as sysdba
Connected to an idle instance.
SQL> startup;
ORA-00845: MEMORY_TARGET not supported on this system

I followed the following document

http://forums.oracle.com/forums/thread.jspa?threadID=1113265

I am not at all aware of any command given in this link

I opened a command console ,went to DB_HOME\bin location and did

SQL> startup
ORA-00845: MEMORY_TARGET not supported on this system
SQL> df -k
SP2-0042: unknown command "df -k" - rest of line ignored.
SQL> quit
Disconnected
bash-3.2$ df -k
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/hda2 6092388 3379808 2398108 59% /
/dev/hda3 3050092 77600 2815056 3% /tmp
/dev/hda5 35448964 29045060 4574104 87% /refresh
/dev/hda1 101086 27987 67880 30% /boot
tmpfs 1558032 0 1558032 0% /dev/shm
bash-3.2$ mount -t tmpfs shmfs -o size=2048m /dev/shm
mount: only root can do that
bash-3.2$ su -oracle
su: invalid option -- o
Try `su --help' for more information.
bash-3.2$ su
Password:
su: incorrect password
bash-3.2$ su root
Password:
[root@192-168-203-10 bin]# mount -t tmpfs shmfs -o size=2048m /dev/shm

[root@192-168-203-10 bin]# su oracle
$ su oracle
Password:

$ ./sqlplus

SQL*Plus: Release 11.2.0.1.0 Production on Tue Apr 12 00:54:42 2011

Copyright (c) 1982, 2009, Oracle. All rights reserved.

Enter user-name: sys as sysdba
Enter password:
Connected to an idle instance.

SQL> startup
ORACLE instance started.

Total System Global Area 2042241024 bytes
Fixed Size 1337548 bytes
Variable Size 1342179124 bytes
Database Buffers 687865856 bytes
Redo Buffers 10858496 bytes
Database mounted.
Database opened.
SQL>