---
title: "proc_signal()"
description: "The proc_signal() function is used to send a signal to a specific child process identified by its PID. The signal specified by the sig parameter is sent to the child process, which allows for various forms of inter-process communication and process control."
url: "https://wasix.org/docs/api-reference/wasix/proc_signal/"
markdown: "https://wasix.org/docs/api-reference/wasix/proc_signal.md"
---

# `proc_signal()`

Sends a signal to a child process.

## Description

The `proc_signal()` function is used to send a signal to a specific child process identified by its PID. The signal specified by the `sig` parameter is sent to the child process, which allows for various forms of inter-process communication and process control.

On POSIX systems, a similar functionality is provided by the `kill()` function. It allows sending a signal to a process or a group of processes identified by their process ID. The `kill()` function is part of the POSIX standard and is widely supported across different platforms.

## Syntax

```ebnf
  ;;; Sends a signal to another process
  (@interface func (export "proc_signal")
    ;;; ID of the process to send a singal
    (param $pid $pid)
    ;;; Signal to send to the thread
    (param $signal $signal)
    (result $error (expected (error $errno)))
  )
```

## Parameters

- `ctx`: A mutable reference to the function environment.
- `pid`: The PID of the child process to which the signal will be sent.
- `sig`: The signal to send to the child process.

## Return Value

The function returns a `Result` indicating the success or failure of the operation. If the operation is successful, it returns `Ok(Errno::Success)`. Otherwise, it returns an appropriate `WasiError` value.

## Logging

This function is instrumented with `trace` level logging. It includes the following fields for debugging purposes:

- `pid`: The PID of the child process.
- `sig`: The signal being sent.

## Notes

- The `proc_signal()` function sends a signal to the child process identified by its PID.
- If a process with the specified PID is found, the signal specified by the `sig` parameter is sent to that process.
- On POSIX systems, a similar functionality is provided by the `kill()` function, which allows sending signals to processes identified by their process ID.
- Sending signals to processes enables inter-process communication and process control. Signals can be used for various purposes, such as terminating a process, handling specific events, or requesting actions from the receiving process.

---

[Documentation index](https://wasix.org/llms.txt) · [HTML version](https://wasix.org/docs/api-reference/wasix/proc_signal/)