---
name: "pthread_sigmask"
section: "3"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/pthread_sigmask/3"
---

# pthread\_sigmask(3)

examine and/or change a thread's signal mask

## NAME

**pthread\_sigmask** – examine and/or change a thread's signal mask

## LIBRARY

POSIX Threads Library (libpthread, -lpthread)

## SYNOPSIS

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

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

*int*\

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

## DESCRIPTION

The **pthread\_sigmask**() function examines and/or changes the calling thread's signal mask.

If *set* is not NULL, it specifies a set of signals to be modified, and *how* specifies what to set the signal mask to:

- SIG\_BLOCK

  Union of the current mask and *set*.

- SIG\_UNBLOCK

  Intersection of the current mask and the complement of *set*.

- SIG\_SETMASK

  *set*.

If *oset* is not NULL, the previous signal mask is stored in the location pointed to by *oset*.

SIGKILL and SIGSTOP cannot be blocked, and will be silently ignored if included in the signal mask.

## RETURN VALUES

If successful, **pthread\_sigmask**() returns 0. Otherwise, an error is returned.

## ERRORS

The **pthread\_sigmask**() function will fail if:

- \[EINVAL\]

  *how* is not one of the defined values.

## SEE ALSO

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

## STANDARDS

The **pthread\_sigmask**() function conforms to ISO/IEC 9945-1:1996 (“POSIX.1”)