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35 .Nd "library for PID files handling"
42 .Fn pidfile_open "const char *path" "mode_t mode" "pid_t *pidptr"
44 .Fn pidfile_write "struct pidfh *pfh"
46 .Fn pidfile_close "struct pidfh *pfh"
48 .Fn pidfile_remove "struct pidfh *pfh"
52 family of functions allows daemons to handle PID files.
55 to lock a pidfile and detect already running daemons.
59 function opens (or creates) a file specified by the
61 argument and locks it.
62 If a file can not be locked, a PID of an already running daemon is returned in
65 argument (if it is not
67 The function does not write process' PID into the file here, so it can be
70 and exit with a proper error message when needed.
75 .Pa /var/run/ Ns Ao Va progname Ac Ns Pa .pid
80 function writes process' PID into a previously opened file.
84 function closes a pidfile.
85 It should be used after daemon
87 to start a child process.
91 function closes and removes a pidfile.
95 function returns a valid pointer to a
97 structure on success, or
104 .Rv -std pidfile_write pidfile_close pidfile_remove
106 The following example shows in which order these functions should be used.
107 Note that it is safe to pass
117 pid_t otherpid, childpid;
119 pfh = pidfile_open("/var/run/daemon.pid", 0600, &otherpid);
121 if (errno == EEXIST) {
122 errx(EXIT_FAILURE, "Daemon already running, pid: %jd.",
125 /* If we cannot create pidfile from other reasons, only warn. */
126 warn("Cannot open or create pidfile");
129 if (daemon(0, 0) == -1) {
130 warn("Cannot daemonize");
142 syslog(LOG_ERR, "Cannot fork(): %s.", strerror(errno));
149 syslog(LOG_INFO, "Child %jd started.", (intmax_t)childpid);
160 function will fail if:
163 Some process already holds the lock on the given pidfile, meaning that a
164 daemon is already running.
165 .It Bq Er ENAMETOOLONG
166 Specified pidfile's name is too long.
168 Some process already holds the lock on the given pidfile, but PID read
169 from there is invalid.
171 Some process already holds the lock on the given pidfile, but the file
173 Most likely, the existing daemon is writing new PID into
179 function may also fail and set
181 for any errors specified for the
190 function will fail if:
193 Improper function use.
194 Probably called before
200 function may also fail and set
202 for any errors specified for the
211 function may fail and set
213 for any errors specified for the
221 function will fail if:
224 Improper function use.
225 Probably called not from the process which made
231 function may also fail and set
233 for any errors specified for the
250 functionality is based on ideas from
251 .An John-Mark Gurney Aq jmg@FreeBSD.org .
253 The code and manual page was written by
254 .An Pawel Jakub Dawidek Aq pjd@FreeBSD.org .