Ignoring signals

If we want the shell to ignore certain signals, then we can call the trap command followed by a pair of empty quotes as a command. Those signals will be ignored by the shell process shown by either of the following commands:

    $ trap " " 2 3 20
    $ trap " " INT QUIT TSTP

The signals 2 (SIGINT), 3 (SIGQUIT), and 20 (SIGTSTP) will be ignored by the shell process.

Resetting signals

If we want to reset the signal behavior to the original default action, then we need to call the trap command followed by the signal name or number as shown in the following examples, respectively:

    $ trap TSTP
    $ trap 20

This will reset the default action of signal 20 (SIGTSTP). The default action is...