---
name: "daemon"
section: "3"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
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*);

*int*\

**daemonfd**(*int chdirfd*, *int nullfd*);

## 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).

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

If the argument *noclose* is zero, **daemon**() redirects standard input, standard output, and standard error to */dev/null*.

The **daemonfd**() function is equivalent to the **daemon**() function except that arguments are the descriptors for the current working directory and to the descriptor to */dev/null*.

If *chdirfd* is equal to (-1) the current working directory is not changed.

If *nullfd* is equals to (-1) the redirection of standard input, standard output, and standard error is not closed.

## RETURN VALUES

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

## SEE ALSO

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

## HISTORY

The **daemon**() function first appeared in 4.4BSD. The **daemonfd**() function first appeared in FreeBSD 12.0.

## CAVEATS

In multithreaded programs, the child process after **fork**() inherits copies of all mutexes and other synchronization state, but only the calling thread survives. Any locks held by other threads at the time of the call will remain permanently acquired in the child, causing deadlocks in any code that attempts to acquire them. Until one of the [exec(3)](/exec/3.md) functions is called, the child should restrict itself to async-signal safe operations (see [sigaction(2)](/sigaction/2.md)).

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.