Hello Pradeep,
Just to avoid anything being lost in translation.
Q) When you ran "touch DELME" as <sidadm> in /tmp, what message/error did you get ?
A)
Q) Did you try the "touch" as user "root" ?
A)
Q) Have you checked your /var/log/messages file ?
A)
As Martin already pointed out and your reply seems to confirm this, this is not a HANA problem but a o/s problem.
Find out what's not right with your /tmp with your o/s admin (worrying as /tmp is on root filesystem). They may want to run a fsck in dry run mode on "/"
Kind Regards,
Amerjit