---
name: "sigprocmask"
section: "2"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/sigprocmask"
---

# sigprocmask(2)

manipulate current signal mask

## NAME

**sigprocmask** – manipulate current signal mask

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

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

*int*\

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

## DESCRIPTION

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 ⟨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.

In threaded applications, [pthread\_sigmask(3)](/pthread_sigmask/3.md) must be used instead of **sigprocmask**().

## RETURN VALUES

The **sigprocmask()** function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

## ERRORS

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.

## SEE ALSO

[kill(2)](/kill/2.md), [sigaction(2)](/sigaction/2.md), [sigpending(2)](/sigpending/2.md), [sigsuspend(2)](/sigsuspend/2.md), [fpsetmask(3)](/fpsetmask/3.md), [pthread\_sigmask(3)](/pthread_sigmask/3.md), [sigsetops(3)](/sigsetops/3.md)

## STANDARDS

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