---
name: "daemon"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/daemon/3"
---

# daemon(3)

run in the background

## NAME

**daemon** – run in the background

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

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

*int*\

**daemon**(*int nochdir*, *int noclose*);

## DESCRIPTION

The **daemon**() function is for programs wishing to detach themselves from the controlling terminal and run in the background as system daemons. The [fork(2)](/fork/2.md) system call is used; see CAVEATS below about the environment after a **fork**() (without a corresponding call to one of the exec routines). On Mac OS X, the use of this API is discouraged in favor of using launchd(8).

Unless the argument *nochdir* is non-zero, **daemon**() changes the current working directory to the root (*/*).

Unless the argument *noclose* is non-zero, **daemon**() will redirect standard input, standard output, and standard error to */dev/null*.

## RETURN VALUES

The **daemon()** 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 **daemon**() function may fail and set *errno* for any of the errors specified for the library functions [fork(2)](/fork/2.md) and [setsid(2)](/setsid/2.md).

## SEE ALSO

[fork(2)](/fork/2.md), launchd(8), [setsid(2)](/setsid/2.md), [sigaction(2)](/sigaction/2.md)

## HISTORY

The **daemon**() function first appeared in 4.4BSD.

## CAVEATS

There are limits to what you can do in the child process. To be totally safe you should restrict yourself to only executing async-signal safe operations (see [sigaction(2)](/sigaction/2.md)) until such time as one of the exec functions is called. All APIs, including global data symbols, in any framework or library should be assumed to be unsafe after a  **fork**() unless explicitly documented to be safe or async-signal safe. If you need to use these frameworks in the child  process, you must exec. In this situation it is reasonable to exec yourself.

Unless the *noclose* argument is non-zero, **daemon**() will close the first three file descriptors and redirect them to */dev/null*. Normally, these correspond to standard input, standard output, and standard error. However, if any of those file descriptors refer to something else, they will still be closed, resulting in incorrect behavior of the calling program. This can happen if any of standard input, standard output, or standard error have been closed before the program was run. Programs using **daemon**() should therefore either call **daemon**() before opening any files or sockets, or verify that any file descriptors obtained have values greater than 2.

The **daemon**() function temporarily ignores SIGHUP while calling [setsid(2)](/setsid/2.md) to prevent a parent session group leader's calls to [fork(2)](/fork/2.md) and then [\_exit(2)](/_exit/2.md) from prematurely terminating the child process.