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pidfile (3)

>> pidfile (3) ( FreeBSD man: Библиотечные вызовы )

BSD mandoc

NAME



pidfile_open

 
pidfile_write

 
pidfile_close

 
pidfile_remove

 - library for PID files handling

LIBRARY

Lb libutil

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 flock(2) to lock a pidfile and detect already running daemons.

The pidfile_open ();
function opens (or creates) a file specified by the Fa path argument and locks it with the flock(2) system call. 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 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 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 (Ns 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 Vt pidfh structure on success, or NULL if an error occurs. If an error occurs, errno will be set. Rv -std pidfile_write pidfile_close pidfile_remove

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:

Bq Er EEXIST: Some process already holds the lock on the given pidfile, meaning that a daemon is already running.
Bq Er ENAMETOOLONG: Specified pidfile's name is too long.
Bq Er EINVAL: Some process already holds the lock on the given pidfile, but PID read from there is invalid.
Bq Er EAGAIN: Some process already holds the lock on the given pidfile, but the file is truncated. Most likely, the existing 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:

Bq Er 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:

Bq Er 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), flock(2), fstat(2), write(2), and unlink(2) calls.