Q:

Signal without any default action except SIGINFO

Is there any signal with no default action except SIGINFO.  This link suggests that even SIGPWR default's action is to terminate the process.  My requirement is to handle the signal only when there is a custom signal handler present, otherwise ignore the signal. 

A:

See man 7 signal for a list of all signals and their default dispositions.   Currently I see these as being ignored by default:
   Signal     Value     Action   Comment
   ──────────────────────────────────────────────────────────────
   SIGCHLD    20,17,18    Ign    Child stopped or terminated
   SIGURG     16,23,21    Ign    Urgent condition on socket (4.2BSD)
   SIGWINCH   28,28,20    Ign    Window resize signal (4.3BSD, Sun)

As you can see, there are really not many choices.   I would say that of the above, SIGCHLD might be OK if you are sure you have no child processes, or SIGURG if you are sure you have no sockets which might be signaled that way.   Finally, SIGWINCH is only appropriate if you are sure your program will not have a controlling terminal which could be resized.