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PIDFILE(3)	       FreeBSD 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 <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);

     int
     pidfile_fileno(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 pidptr argument is	not NULL and file can
     not be locked, the	function will use it to	store a	PID of an already run-
     ning daemon or -1 in case daemon did not write its	PID yet.  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_open() function sets the O_CLOEXEC	close-on-exec flag when	open-
     ing the pidfile.

     The pidfile_write() function writes process' PID into a previously	opened
     file.  The	file is	truncated before write,	so calling the pidfile_write()
     function multiple times is	supported.

     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.

     The pidfile_fileno() function returns the file descriptor for the open
     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
     return the	value 0	if successful; otherwise the value -1 is returned and
     the global	variable errno is set to indicate the error.

     The pidfile_fileno() function returns the low-level file descriptor.  It
     returns -1	and sets errno if a NULL pidfh is specified, or	if the pidfile
     is	no longer open.

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(), pidfile_close() and pidfile_fileno() 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");
	     /*
	      *	Eventhough pfh is NULL we can continue,	as the other pidfile_*
	      *	function can handle such situation by doing nothing except setting
	      *	errno to EDOOFUS.
	      */
     }

     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.	 If
			pidptr argument	is not NULL the	function will use it
			to store a PID of an already running daemon or -1 in
			case daemon did	not write its PID yet.

     [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.

     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.

     The pidfile_fileno() function will	fail if:

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

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>.

FreeBSD	10.1		       February	8, 2012			  FreeBSD 10.1

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | EXAMPLES | ERRORS | SEE ALSO | AUTHORS

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