First run following command to see if dual core kernel installed or not:

$ uname -r

OR

$ uname –a

Output

2.6.9-42.0.8.ELsmp

If you don’t see smp kernel word in output install smp kernel using apt-get, rpm or up2date command. For example following command will install smp kernel under RedHat Linux:

# up2date kernel-smp-2.6.9-42.EL

Now reboot system and boot using new SMP kernel. With new kernel you should see dual core enabled.