The Fn pidfile_open function opens (or creates) a file specified by the Fa path argument and locks it. If a file can not be locked, a PID of an already running daemon is returned in the Fa pidptr argument (if it is not NULL ) The function does not write process' PID into the file here, so it can be used before Fn fork Ns ing and exit with a proper error message when needed. If the Fa path argument is NULL /var/run/ Ao progname Ac .pid file will be used.
The Fn pidfile_write function writes process' PID into a previously opened file.
The Fn pidfile_close function closes a pidfile. It should be used after daemon Fn fork Ns s to start a child process.
The Fn pidfile_remove function closes and removes a pidfile.
Rv -std pidfile_write pidfile_close pidfile_remove
struct pidfh *pfh; pid_t otherpid, childpid; pfh = pidfile_open("/var/run/daemon.pid", 0600, &otherpid); if (pfh == NULL) { if (errno == EEXIST) { errx(EXIT_FAILURE, "Daemon already running, pid: %jd.", (intmax_t)otherpid); } /* If we cannot create pidfile from other reasons, only warn. */ warn("Cannot open or create pidfile"); } if (daemon(0, 0) == -1) { warn("Cannot daemonize"); pidfile_remove(pfh); exit(EXIT_FAILURE); } pidfile_write(pfh); for (;;) { /* Do work. */ childpid = fork(); switch (childpid) { case -1: syslog(LOG_ERR, "Cannot fork(): %s.", strerror(errno)); break; case 0: pidfile_close(pfh); /* Do child work. */ break; default: syslog(LOG_INFO, "Child %jd started.", (intmax_t)childpid); break; } } pidfile_remove(pfh); exit(EXIT_SUCCESS);
The Fn pidfile_open function may also fail and set errno for any errors specified for the fstat(2), open(2), and read(2) calls.
The Fn pidfile_write function will fail if:
The Fn pidfile_write function may also fail and set errno for any errors specified for the fstat(2), ftruncate(2), and write(2) calls.
The Fn pidfile_close function may fail and set errno for any errors specified for the close(2) and fstat(2) calls.
The Fn pidfile_remove function will fail if:
The Fn pidfile_remove function may also fail and set errno for any errors specified for the close(2), fstat(2), write(2), and unlink(2) system calls and the flopen(3) library function.
The code and manual page was written by An Pawel Jakub Dawidek Aq pjd@FreeBSD.org .