man.bsd.lv manual page server

NAME

pidfile_open, pidfile_write, pidfile_close, pidfile_remove — library for PID files handling

LIBRARY

library “libutil”

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);

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");
	/*
	 * Even though 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>.