1. daemon
#inlcude <unistd.h>
int daemon(int nochdir, int noclose);
The daemon() function is for programs wishing to detach themselves from the controlling terminal and run in the background as system daemons. If nochdir is zero, daemon() changes the calling process's current working directory to the root directory ("/"); otherwise, the current working directory is left unchanged. If noclose is zero, daemon() redirects standard input, standard output and standard error to /dev/null; otherwise, no changes are made to these file descriptors.
(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 errno to any of the errors specified for the fork(2) and setsid(2).
創建新進程，父進程退出http://man7.org/linux/man-pages/man3/daemon.3.html
2.
sched_setscheduler
sched_getscheduler
3. sigaction