sigprocmask(2)sigprocmask(2)NAMEsigprocmask() - examine and change blocked signals
The function allows the calling thread to examine and/or change its
If the argument set is not a null pointer, it points to a set of sig‐
nals to be used to change the currently blocked set.
The argument how indicates the way in which the set is changed and con‐
sists of one of the following values:
The resulting set will be the union
of the current set and the signal set pointed
to by set.
The resulting set will be the signal set pointed to by set.
The resulting set will be the intersection of the
current set and the complement of the signal
set pointed to by set.
If the argument oset is not a null pointer, the previous mask is stored
in the location pointed to by oset. If set is a null pointer, the
value of the argument how is not significant and the thread's signal
mask is unchanged; thus the call can be used to inquire about currently
If there are any pending unblocked signals after the call to at least
one of those signals will be delivered before the call to returns.
It is not possible to block those signals which cannot be
ignored. This is enforced by the system without causing an error to be
If any of the or signals are generated while they are blocked, the
result is undefined, unless the signal was generated by a call to or
If fails, the thread's signal mask is not changed.
Upon successful completion, returns 0. Otherwise −1 is returned, is
set to indicate the error, and the thread's signal mask will be
The function will fail if:
The value of the
how argument is not equal to one of the defined
set or oset points to an invalid address. The reli‐
able detection of this error is implementation
Each thread maintains its own blocked signal mask. In a single-
threaded process, modifies only the calling thread's blocked signal
Use of this function is unspecified in a multithreaded process.
For more information regarding signals and threads, refer to signal(5).
LWP (Lightweight Processes) Considerations
modifies only the calling LWP's blocked signal mask.
was derived from the IEEE POSIX 1003.1-1988 Standard.
SEE ALSOsigaction(2), sigpending(2), sigsuspend(2), sigsetops(3C), pthread_sig‐