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$FreeBSD: head/lib/libutil/pidfile.3 156280 2006-03-04 15:20:28Z keramida $
.Dd August 22, 2005 .Dt PIDFILE 3 .Os .Sh NAME .Nm pidfile_open , .Nm pidfile_write , .Nm pidfile_close , .Nm pidfile_remove .Nd "library for PID files handling" .Sh LIBRARY .Lb libutil .Sh SYNOPSIS n sys/param.h n libutil.h .Ft "struct pidfh *" .Fn pidfile_open "const char *path" "mode_t mode" "pid_t *pidptr" .Ft int .Fn pidfile_write "struct pidfh *pfh" .Ft int .Fn pidfile_close "struct pidfh *pfh" .Ft int .Fn pidfile_remove "struct pidfh *pfh" .Sh DESCRIPTION The .Nm pidfile family of functions allows daemons to handle PID files. It uses .Xr flock 2 to lock a pidfile and detect already running daemons.
p The .Fn pidfile_open function opens (or creates) a file specified by the .Fa path argument and locks it with the .Xr 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 .Dv NULL ) . The function does not write process' PID into the file here, so it can be used before .Fn fork Ns ing and exit with a proper error message when needed. If the .Fa path argument is .Dv NULL ,
a /var/run/ Ns Ao Va progname Ac Ns Pa .pid file will be used.
p The .Fn pidfile_write function writes process' PID into a previously opened file.
p The .Fn pidfile_close function closes a pidfile. It should be used after daemon .Fn fork Ns s to start a child process.
p The .Fn pidfile_remove function closes and removes a pidfile. .Sh RETURN VALUES The .Fn pidfile_open function returns a valid pointer to a .Vt pidfh structure on success, or .Dv NULL if an error occurs. If an error occurs, .Va errno will be set. .Rv -std pidfile_write pidfile_close pidfile_remove .Sh EXAMPLES The following example shows in which order these functions should be used. Note that it is safe to pass .Dv NULL to .Fn pidfile_write , .Fn pidfile_remove and .Fn pidfile_close functions. d -literal 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); .Ed .Sh ERRORS The .Fn pidfile_open function will fail if: l -tag -width Er t Bq Er EEXIST Some process already holds the lock on the given pidfile, meaning that a daemon is already running. t Bq Er ENAMETOOLONG Specified pidfile's name is too long. t Bq Er EINVAL Some process already holds the lock on the given pidfile, but PID read from there is invalid. .El
p The .Fn pidfile_open function may also fail and set .Va errno for any errors specified for the .Xr fstat 2 , .Xr open 2 , and .Xr read 2 calls.
p The .Fn pidfile_write function will fail if: l -tag -width Er t Bq Er EDOOFUS Improper function use. Probably called before .Fn pidfile_open . .El
p The .Fn pidfile_write function may also fail and set .Va errno for any errors specified for the .Xr fstat 2 , .Xr ftruncate 2 , and .Xr write 2 calls.
p The .Fn pidfile_close function may fail and set .Va errno for any errors specified for the .Xr close 2 and .Xr fstat 2 calls.
p The .Fn pidfile_remove function will fail if: l -tag -width Er t Bq Er EDOOFUS Improper function use. Probably called not from the process which made .Fn pidfile_write . .El
p The .Fn pidfile_remove function may also fail and set .Va errno for any errors specified for the .Xr close 2 , .Xr flock 2 , .Xr fstat 2 , .Xr write 2 , and .Xr unlink 2 calls. .Sh SEE ALSO .Xr flock 2 , .Xr open 2 , .Xr daemon 3 .Sh AUTHORS .An -nosplit The .Nm pidfile functionality is based on ideas from .An John-Mark Gurney Aq jmg@FreeBSD.org .
p The code and manual page was written by .An Pawel Jakub Dawidek Aq pjd@FreeBSD.org .