man3/daemon.3

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  32 .\"     @(#)daemon.3    8.1 (Berkeley) 6/9/93
  33 .\" Added mentioning of glibc weirdness wrt unistd.h. 5/11/98, Al Viro
  34 .TH DAEMON 3 2007-07-26 "GNU" "Linux Programmer's Manual"
  35 .SH NAME
  36 daemon \- run in the background
  37 .SH SYNOPSIS
  38 .B #include <unistd.h>
  39 .sp
  40 .BI "int daemon(int " nochdir ", int " noclose );
  41 .sp
  42 .in -4n
  43 Feature Test Macro Requirements for glibc (see
  44 .BR feature_test_macros (7)):
  45 .in
  46 .sp
  47 .BR daemon ():
  48 _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE\ <\ 500)
  49 .SH DESCRIPTION
  50 The
  51 .BR daemon ()
  52 function is for programs wishing to detach themselves from the
  53 controlling terminal and run in the background as system daemons.
  54 .PP
  55 Unless the argument
  56 .I nochdir
  57 is non-zero,
  58 .BR daemon ()
  59 changes the current working directory to the root ("/").
  60 .PP
  61 Unless the argument
  62 .I noclose
  63 is non-zero,
  64 .BR daemon ()
  65 will redirect standard input, standard output and standard error
  66 to \fI/dev/null\fP.
  67 .SH "RETURN VALUE"
  68 (This function forks, and if the
  69 .BR fork (2)
  70 succeeds, the parent calls
  71 .\" not .IR in order not to underline _
  72 .BR _exit (2),
  73 so that further errors are seen by the child only.)
  74 On success zero will be returned.
  75 If an error occurs,
  76 .BR daemon ()
  77 returns \-1 and sets the global variable
  78 .I errno
  79 to any of the errors specified for the
  80 .BR fork (2)
  81 and
  82 .BR setsid (2).
  83 .SH CONFORMING TO
  84 Not in POSIX.1-2001.
  85 A similar function appears on the BSDs.
  86 The
  87 .BR daemon ()
  88 function first appeared in 4.4BSD.
  89 .SH NOTES
  90 The glibc implementation can also return \-1 when
  91 .I /dev/null
  92 exists but is not a character device with the expected
  93 major and minor numbers.
  94 In this case
  95 .I errno
  96 need not be set.
  97 .SH "SEE ALSO"
  98 .BR fork (2),
  99 .BR setsid (2)