Manpage of DAEMON
DAEMONSection: Linux Programmer's Manual (3)
NAMEdaemon - run in the background
int daemon(int nochdir, int noclose);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
Since glibc 2.21: _DEFAULT_SOURCE In glibc 2.19 and 2.20: _DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500) Up to and including glibc 2.19: _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
DESCRIPTIONThe daemon() function is for programs wishing to detach themselves from the controlling terminal and run in the background as system daemons.
If nochdiris zero, daemon() changes the process's current working directory to the root directory ("/"); otherwise, the current working directory is left unchanged.
RETURN VALUE(This function forks, and if the fork(2) succeeds, the parent calls _exit(2), so that further errors are seen by the child only.) On success daemon() returns zero. If an error occurs, daemon() returns -1 and sets errnoto any of the errors specified for the fork(2) and setsid(2).
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
CONFORMING TONot in POSIX.1. A similar function appears on the BSDs. The daemon() function first appeared in 4.4BSD.
NOTESThe glibc implementation can also return -1 when /dev/nullexists but is not a character device with the expected major and minor numbers. In this case, errnoneed not be set.
BUGSThe GNU C library implementation of this function was taken from BSD, and does not employ the double-fork technique (i.e., fork(2), setsid(2), fork(2)) that is necessary to ensure that the resulting daemon process is not a session leader. Instead, the resulting daemon isa session leader. On systems that follow System V semantics (e.g., Linux), this means that if the daemon opens a terminal that is not already a controlling terminal for another session, then that terminal will inadvertently become the controlling terminal for the daemon.
SEE ALSOfork(2), setsid(2)
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