Standard C Library (libc, -lc)

The sigprocmask system call 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 how argument. 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 from #include <signal.h>

• 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.

The sigprocmask system call will fail and the signal mask will be unchanged if one of the following occurs:

• [EINVAL] The how argument has a value other than those listed here.

kill(2), sigaction(2), sigpending(2), sigsuspend(2), fpsetmask(3), sigsetops(3)

The sigprocmask system call is expected to conform to ISO/IEC 9945-1:1990 ("POSIX.1")