daemon(3) [freebsd man page]

DAEMON(3)						   BSD Library Functions Manual 						 DAEMON(3)

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.

     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) and setsid(2).

SEE ALSO

     fork(2), setsid(2), sigaction(2)

HISTORY

     The daemon() function first appeared in 4.4BSD.

CAVEATS

     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 out-
     put, 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) to prevent a parent session group leader's calls to fork(2) and then
     _exit(2) from prematurely terminating the child process.

BSD
								   June 9, 1993 							       BSD

setsid(2)							   System Calls 							 setsid(2)

NAME

       setsid - create session and set process group ID

SYNOPSIS

       #include <sys/types.h>
       #include <unistd.h>

       pid_t setsid(void);

DESCRIPTION

       The  setsid() function creates a new session, if the calling process is not a process group leader. Upon return the calling process will be
       the session leader of this new session, will be the process group leader of a new process group, and will have no controlling terminal. The
       process	group	ID of the calling process will be set equal to the process ID of the calling process. The calling process will be the only
       process in the new process group and the only process in the new session.

RETURN VALUES

       Upon successful completion, setsid() returns the value of the process group  ID of the calling process. Otherwise it returns (pid_t)-1  and
       sets errno to indicate the error.

ERRORS

       The setsid() function will fail if:

       EPERM	The  calling  process  is  already  a  process	group leader, or the process group  ID of a process other than the calling process
		matches the process  ID of the calling process.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Async-Signal-Safe 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       getsid(2), setpgid(2), setpgrp(2), attributes(5), standards(5)

WARNINGS

       A call to setsid() by a process that is a process group leader will fail. A process can become a process group leader  by  being  the  last
       member of a pipeline started by a job control shell. Thus, a process that expects to be part of a pipeline, and that calls setsid(), should
       always first fork; the parent should exit and the child should call setsid(). This will ensure that the calling process will work  reliably
       when started by both job control shells and non-job control shells.

SunOS 5.11							    21 Aug 2002 							 setsid(2)