---
name: "pthread_sigmask"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/pthread_sigmask/3"
---

# pthread\_sigmask(3)

examine and change mask of blocked signals

## NAME

pthread\_sigmask - examine and change mask of blocked signals

## LIBRARY

POSIX threads library (*libpthread*, *-lpthread*)

## SYNOPSIS

```
#include <signal.h>
```

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

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**pthread\_sigmask**():

```
    _POSIX_C_SOURCE >= 199506L || _XOPEN_SOURCE >= 500
```

## DESCRIPTION

The **pthread\_sigmask**() function is just like [**sigprocmask**(2)](/sigprocmask/2.md), with the difference that its use in multithreaded programs is explicitly specified by POSIX.1. Other differences are noted in this page.

For a description of the arguments and operation of this function, see [**sigprocmask**(2)](/sigprocmask/2.md).

## RETURN VALUE

On success, **pthread\_sigmask**() returns 0; on error, it returns an error number.

## ERRORS

See [**sigprocmask**(2)](/sigprocmask/2.md).

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **pthread\_sigmask**() | Thread safety | MT-Safe |

## STANDARDS

POSIX.1-2008.

## HISTORY

POSIX.1-2001.

## NOTES

A new thread inherits a copy of its creator's signal mask.

The glibc **pthread\_sigmask**() function silently ignores attempts to block the two real-time signals that are used internally by the NPTL threading implementation. See [**nptl**(7)](/nptl/7.md) for details.

## EXAMPLES

The program below blocks some signals in the main thread, and then creates a dedicated thread to fetch those signals via [**sigwait**(3)](/sigwait/3.md). The following shell session demonstrates its use:

```
$ ./a.out &
[1] 5423
$ kill -QUIT %1
Signal handling thread got signal 3
$ kill -USR1 %1
Signal handling thread got signal 10
$ kill -TERM %1
[1]+  Terminated              ./a.out
```

### Program source

```
#include <err.h>
#include <errno.h>
#include <pthread.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
/* Simple error handling functions */
static void *
sig_thread(void *arg)
{
    sigset_t *set = arg;
    int s, sig;
    for (;;) {
        s = sigwait(set, &sig);
        if (s != 0)
            errc(EXIT_FAILURE, s, "sigwait");
        printf("Signal handling thread got signal %d\n", sig);
    }
}
int
main(void)
{
    pthread_t thread;
    sigset_t set;
    int s;
    /* Block SIGQUIT and SIGUSR1; other threads created by main()
       will inherit a copy of the signal mask.  */
    sigemptyset(&set);
    sigaddset(&set, SIGQUIT);
    sigaddset(&set, SIGUSR1);
    s = pthread_sigmask(SIG_BLOCK, &set, NULL);
    if (s != 0)
        errc(EXIT_FAILURE, s, "pthread_sigmask");
    s = pthread_create(&thread, NULL, &sig_thread, &set);
    if (s != 0)
        errc(EXIT_FAILURE, s, "pthread_create");
    /* Main thread carries on to create other threads and/or do
       other work.  */
    pause();            /* Dummy pause so we can test program */
}
```

## SEE ALSO

[**sigaction**(2)](/sigaction/2.md), [**sigpending**(2)](/sigpending/2.md), [**sigprocmask**(2)](/sigprocmask/2.md), [**pthread\_attr\_setsigmask\_np**(3)](/pthread_attr_setsigmask_np/3.md), [**pthread\_create**(3)](/pthread_create/3.md), [**pthread\_kill**(3)](/pthread_kill/3.md), [**sigsetops**(3)](/sigsetops/3.md), [**pthreads**(7)](/pthreads/7.md), [**signal**(7)](/signal/7.md)