This macro returns a signal mask that has the bit for signal signum set. You can bitwise-OR the results of several calls to sigmask together to specify more than one signal. For example,

          (sigmask (SIGTSTP) | sigmask (SIGSTOP)
           | sigmask (SIGTTIN) | sigmask (SIGTTOU))
     

specifies a mask that includes all the job-control stop signals.

This function is equivalent to sigprocmask (see Process Signal Mask) with a how argument of SIG_BLOCK: it adds the signals specified by mask to the calling process's set of blocked signals. The return value is the previous set of blocked signals.

This function equivalent to sigprocmask (see Process Signal Mask) with a how argument of SIG_SETMASK: it sets the calling process's signal mask to mask. The return value is the previous set of blocked signals.

This function is the equivalent of sigsuspend (see Waiting for a Signal): it sets the calling process's signal mask to mask, and waits for a signal to arrive. On return the previous set of blocked signals is restored.