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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
     running 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
     opening 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
                        pidfile, 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
                        pidfile, 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
     specified 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 11.0-PRERELEASE        February 8, 2012        FreeBSD 11.0-PRERELEASE

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

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