After searching all over the internet, I came know where to alter the values of PATH variable in case of interactive/non-interactive - login/non-login shell combinations.
Found from another post
https://shreevatsa.wordpress.com/2008/03/30/zshbash-startup-files-loading-order-bashrc-zshrc-etc/
I have "/bin/sh" as default login shell and only /etc/profile file is being used to export all needed environment variables in my system. And in case of non-interactive login shell, /etc/profile is not being referred too, even though above link says it would. But still when I execute,
ssh -4 -q -o StrictHostKeyChecking=no root@xxxx "env"
Password:
SHELL=/bin/sh
...
**PATH=/usr/bin:/bin:/usr/sbin:/sbin**
...
I could see some default values for PATH variable. I would like to know where exactly these default values of PATH are being set.