---
name: "pthread_kill"
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_kill/3"
---

# pthread\_kill(3)

send a signal to a thread

## NAME

pthread\_kill - send a signal to a thread

## LIBRARY

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

## SYNOPSIS

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

**int pthread\_kill(pthread\_t** *thread***, int** *sig***);**

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

**pthread\_kill**():

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

## DESCRIPTION

The **pthread\_kill**() function sends the signal *sig* to *thread*, a thread in the same process as the caller. The signal is asynchronously directed to *thread*.

If *sig* is 0, then no signal is sent, but error checking is still performed.

## RETURN VALUE

On success, **pthread\_kill**() returns 0; on error, it returns an error number, and no signal is sent.

## ERRORS

- **EINVAL**

  An invalid signal was specified.

## ATTRIBUTES

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

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

## VERSIONS

The glibc implementation of **pthread\_kill**() gives an error (**EINVAL**) on attempts to send either of the real-time signals used internally by the NPTL threading implementation. See [**nptl**(7)](/nptl/7.md) for details.

POSIX.1-2008 recommends that if an implementation detects the use of a thread ID after the end of its lifetime, **pthread\_kill**() should return the error **ESRCH**. The glibc implementation returns this error in the cases where an invalid thread ID can be detected. But note also that POSIX says that an attempt to use a thread ID whose lifetime has ended produces undefined behavior, and an attempt to use an invalid thread ID in a call to **pthread\_kill**() can, for example, cause a segmentation fault.

## STANDARDS

POSIX.1-2008.

## HISTORY

POSIX.1-2001.

## NOTES

Signal dispositions are process-wide: if a signal handler is installed, the handler will be invoked in the thread *thread*, but if the disposition of the signal is "stop", "continue", or "terminate", this action will affect the whole process.

## SEE ALSO

[**kill**(2)](/kill/2.md), [**sigaction**(2)](/sigaction/2.md), [**sigpending**(2)](/sigpending/2.md), [**pthread\_self**(3)](/pthread_self/3.md), [**pthread\_sigmask**(3)](/pthread_sigmask/3.md), [**raise**(3)](/raise/3.md), [**pthreads**(7)](/pthreads/7.md), [**signal**(7)](/signal/7.md)