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daemon(3) [osx man page]

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

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. 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) 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

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setsid(2)							   System Calls 							 setsid(2)

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 5.10 21 Aug 2002 setsid(2)
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