The
sigprocmask() function examines and/or changes the current signal mask (those signals that are blocked from delivery). Signals are blocked if they are members of the current signal mask set.
If
set is not null, the action of
sigprocmask() depends on the value of the parameter
how. The signal mask is changed as a function of the specified
set and the current mask. The function is specified by
how using one of the following values:
SIG_BLOCK
The new mask is the union of the current mask and the specified set.
SIG_UNBLOCK
The new mask is the intersection of the current mask and the complement of the specified set.
SIG_SETMASK
The current mask is replaced by the specified set.
If
oset is not null, it is set to the previous value of the signal mask.
When
set is null, the value of
how is insignificant and the mask remains unset providing a way to examine the signal mask without modification.
The system quietly disallows
SIGKILL or
SIGSTOP to be blocked.