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4 .\" %%%LICENSE_START(BSD_4_CLAUSE_UCB)
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34 .\" @(#)daemon.3 8.1 (Berkeley) 6/9/93
35 .\" Added mentioning of glibc weirdness wrt unistd.h. 5/11/98, Al Viro
36 .TH DAEMON 3 2017-11-26 "GNU" "Linux Programmer's Manual"
38 daemon \- run in the background
40 .B #include <unistd.h>
42 .BI "int daemon(int " nochdir ", int " noclose );
45 Feature Test Macro Requirements for glibc (see
46 .BR feature_test_macros (7)):
52 .\" commit 266865c0e7b79d4196e2cc393693463f03c90bd8
54 In glibc 2.19 and 2.20:
55 _DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE\ <\ 500)
56 Up to and including glibc 2.19:
57 _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE\ <\ 500)
62 function is for programs wishing to detach themselves from the
63 controlling terminal and run in the background as system daemons.
69 changes the process's current working directory
70 to the root directory ("/");
71 otherwise, the current working directory is left unchanged.
77 redirects standard input, standard output and standard error
80 otherwise, no changes are made to these file descriptors.
82 (This function forks, and if the
84 succeeds, the parent calls
85 .\" not .IR in order not to underline _
87 so that further errors are seen by the child only.)
95 to any of the errors specified for the
100 For an explanation of the terms used in this section, see
106 Interface Attribute Value
109 T} Thread safety MT-Safe
113 A similar function appears on the BSDs.
116 function first appeared in 4.4BSD.
118 The glibc implementation can also return \-1 when
120 exists but is not a character device with the expected
121 major and minor numbers.
126 The GNU C library implementation of this function was taken from BSD,
127 and does not employ the double-fork technique (i.e.,
131 that is necessary to ensure that the resulting daemon process is
132 not a session leader.
133 Instead, the resulting daemon
136 .\" FIXME . https://sourceware.org/bugzilla/show_bug.cgi?id=19144
137 .\" Tested using a program that uses daemon() and then opens an
138 .\" otherwise unused console device (/dev/ttyN) that does not
139 .\" have an associated getty process.
140 On systems that follow System V semantics (e.g., Linux),
141 this means that if the daemon opens a terminal that is not
142 already a controlling terminal for another session,
143 then that terminal will inadvertently become
144 the controlling terminal for the daemon.