For those who get above error Use python -c ‘import pty;pty.spawn(“/bin/bash”)’ dont use /bin/bash -i . Above error comes when there is no tty … and thanks to @legerdemain for his help. Got root finally 
For those who get above error Use python -c ‘import pty;pty.spawn(“/bin/bash”)’ dont use /bin/bash -i . Above error comes when there is no tty … and thanks to @legerdemain for his help. Got root finally