daemon(3) -- Linux man page
NAMEdaemon - run in the background
DESCRIPTIONThe 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 ("/").
RETURN VALUE(This function forks, and if the fork() succeeds, the parent does _exit(0), so that further errors are seen by the child only.) On success zero will be returned. If an error occurs, daemon() returns -1 and sets the global variable errno to any of the errors specified for the library functions fork(2) and setsid(2).
SEE ALSOfork(2), setsid(2)
NOTESThe glibc implementation can also return -1 when /dev/null exists but is not a character device with the expected major and minor numbers. In this case errno need not be set.
HISTORYThe daemon() function first appeared in BSD4.4.