---
name: "sigprocmask"
section: "2"
platform: "macos"
package: "xnu"
version: "12377.121.6"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/sigprocmask"
---

# sigprocmask(2)

manipulate current signal mask

## NAME

**sigprocmask** – manipulate current signal mask

## SYNOPSIS

**#include \<signal.h\>**

*int*\

**sigprocmask**(*int how*, *const sigset\_t \*restrict set*, *sigset\_t \*restrict oset*);

## DESCRIPTION

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 from ⟨*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.

## RETURN VALUES

A 0 value indicated that the call succeeded.  A -1 return value indicates an error occurred and *errno* is set to indicated the reason.

## ERRORS

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

- \[EINVAL\]

  *how* has a value other than those listed here.

## SEE ALSO

[kill(2)](/kill/2.md), [sigaction(2)](/sigaction/2.md), [sigsuspend(2)](/sigsuspend/2.md), [sigsetops(3)](/sigsetops/3.md)

## STANDARDS

The **sigprocmask**() function call is expected to conform to IEEE Std 1003.1-1988 (“POSIX.1”).