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PIDFILE(3)		 BSD Library Functions Manual		    PIDFILE(3)

NAME
     pidfile_open, pidfile_write, pidfile_close, pidfile_remove	-- library for
     PID files handling

LIBRARY
     System Utilities Library (libutil,	-lutil)

SYNOPSIS
     #include <sys/param.h>
     #include <libutil.h>

     struct pidfh *
     pidfile_open(const	char *path, mode_t mode, pid_t *pidptr);

     int
     pidfile_write(struct pidfh	*pfh);

     int
     pidfile_close(struct pidfh	*pfh);

     int
     pidfile_remove(struct pidfh *pfh);

DESCRIPTION
     The pidfile family	of functions allows daemons to handle PID files.  It
     uses flopen(3) to lock a pidfile and detect already running daemons.

     The pidfile_open()	function opens (or creates) a file specified by	the
     path argument and locks it.  If a file can	not be locked, a PID of	an al-
     ready running daemon is returned in the pidptr argument (if it is not
     NULL).  The function does not write process' PID into the file here, so
     it	can be used before fork()ing and exit with a proper error message when
     needed.  If the path argument is NULL, /var/run/<progname>.pid file will
     be	used.

     The pidfile_write() function writes process' PID into a previously	opened
     file.

     The pidfile_close() function closes a pidfile.  It	should be used after
     daemon fork()s to start a child process.

     The pidfile_remove() function closes and removes a	pidfile.

RETURN VALUES
     The pidfile_open()	function returns a valid pointer to a pidfh structure
     on	success, or NULL if an error occurs.  If an error occurs, errno	will
     be	set.

     The pidfile_write(), pidfile_close(), and pidfile_remove()	functions re-
     turn the value 0 if successful; otherwise the value -1 is returned	and
     the global	variable errno is set to indicate the error.

EXAMPLES
     The following example shows in which order	these functions	should be
     used.  Note that it is safe to pass NULL to pidfile_write(),
     pidfile_remove() and pidfile_close() functions.

     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);

ERRORS
     The pidfile_open()	function will fail if:

     [EEXIST]		Some process already holds the lock on the given pid-
			file, meaning that a daemon is already running.

     [ENAMETOOLONG]	Specified pidfile's name is too	long.

     [EINVAL]		Some process already holds the lock on the given pid-
			file, but PID read from	there is invalid.

     [EAGAIN]		Some process already holds the lock on the given pid-
			file, but the file is truncated.  Most likely, the ex-
			isting daemon is writing new PID into the file.

     The pidfile_open()	function may also fail and set errno for any errors
     specified for the fstat(2), open(2), and read(2) calls.

     The pidfile_write() function will fail if:

     [EDOOFUS]		Improper function use.	Probably called	before
			pidfile_open().

     The pidfile_write() function may also fail	and set	errno for any errors
     specified for the fstat(2), ftruncate(2), and write(2) calls.

     The pidfile_close() function may fail and set errno for any errors	speci-
     fied for the close(2) and fstat(2)	calls.

     The pidfile_remove() function will	fail if:

     [EDOOFUS]		Improper function use.	Probably called	not from the
			process	which made pidfile_write().

     The 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.

SEE ALSO
     open(2), daemon(3), flopen(3)

AUTHORS
     The pidfile functionality is based	on ideas from John-Mark	Gurney
     <jmg@FreeBSD.org>.

     The code and manual page was written by Pawel Jakub Dawidek
     <pjd@FreeBSD.org>.

BSD			       October 20, 2008				   BSD
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | EXAMPLES | ERRORS | SEE ALSO | AUTHORS

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