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$FreeBSD: stable/10/lib/libutil/pidfile.3 231193 2012-02-08 08:49:30Z pjd $
.Dd February 8, 2012 .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 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" .Ft int .Fn pidfile_fileno "struct pidfh *pfh" .Sh DESCRIPTION The .Nm pidfile family of functions allows daemons to handle PID files. It uses .Xr flopen 3 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. If .Fa pidptr argument is not .Dv NULL and file can not be locked, the function will use it to store a PID of an already running daemon or .Li -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 .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. The .Fn pidfile_open function sets the O_CLOEXEC close-on-exec flag when opening the pidfile.
p The .Fn pidfile_write function writes process' PID into a previously opened file. The file is truncated before write, so calling the .Fn pidfile_write function multiple times is supported.
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.
p The .Fn pidfile_fileno function returns the file descriptor for the open 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.
p .Rv -std pidfile_write pidfile_close pidfile_remove
p The .Fn pidfile_fileno function returns the low-level file descriptor. It returns .Li -1 and sets .Va errno if a NULL .Vt pidfh is specified, or if the pidfile is no longer open. .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 , .Fn pidfile_close and .Fn pidfile_fileno 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"); /* * 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); .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. If .Fa pidptr argument is not .Dv NULL the function will use it to store a PID of an already running daemon or .Li -1 in case daemon did not write its PID yet. 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 fstat 2 , .Xr write 2 , and .Xr unlink 2 system calls and the .Xr flopen 3 library function.
p The .Fn pidfile_fileno function will fail if: l -tag -width Er t Bq Er EDOOFUS Improper function use. Probably called not from the process which used .Fn pidfile_open . .El .Sh SEE ALSO .Xr open 2 , .Xr daemon 3 , .Xr flopen 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 .