1.\" Copyright (c) 2005 Pawel Jakub Dawidek <pjd@FreeBSD.org> 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.\" $FreeBSD$ 26.\" 27.Dd August 22, 2005 28.Dt PIDFILE 3 29.Os 30.Sh NAME 31.Nm pidfile_open , 32.Nm pidfile_write , 33.Nm pidfile_close , 34.Nm pidfile_remove 35.Nd "library for PID files handling" 36.Sh LIBRARY 37.Lb libutil 38.Sh SYNOPSIS 39.In sys/param.h 40.In libutil.h 41.Ft "struct pidfh *" 42.Fn pidfile_open "const char *path" "mode_t mode" "pid_t *pidptr" 43.Ft int 44.Fn pidfile_write "struct pidfh *pfh" 45.Ft int 46.Fn pidfile_close "struct pidfh *pfh" 47.Ft int 48.Fn pidfile_remove "struct pidfh *pfh" 49.Sh DESCRIPTION 50The 51.Nm pidfile 52family of functions allows daemons to handle PID files. 53It uses 54.Xr flock 2 55to lock a pidfile and detect already running daemons. 56.Pp 57The 58.Fn pidfile_open 59function opens (or creates) a file specified by the 60.Fa path 61argument and locks it with the 62.Xr flock 2 63system call. 64If a file can not be locked, a PID of an already running daemon is returned in 65the 66.Fa pidptr 67argument (if it is not 68.Dv NULL ) . 69The function does not write process' PID into the file here, so it can be 70used before 71.Fn fork Ns ing 72and exit with a proper error message when needed. 73If the 74.Fa path 75argument is 76.Dv NULL , 77.Pa /var/run/ Ns Ao Va progname Ac Ns Pa .pid 78file will be used. 79.Pp 80The 81.Fn pidfile_write 82function writes process' PID into a previously opened file. 83.Pp 84The 85.Fn pidfile_close 86function closes a pidfile. 87It should be used after daemon 88.Fn fork Ns s 89to start a child process. 90.Pp 91The 92.Fn pidfile_remove 93function closes and removes a pidfile. 94.Sh RETURN VALUES 95The 96.Fn pidfile_open 97function returns a valid pointer to a 98.Vt pidfh 99structure on success, or 100.Dv NULL 101if an error occurs. 102If an error occurs, 103.Va errno 104will be set. 105.Rv -std pidfile_write pidfile_close pidfile_remove 106.Sh EXAMPLES 107The following example shows in which order these functions should be used. 108.Bd -literal 109struct pidfh *pfh; 110pid_t otherpid, childpid; 111 112pfh = pidfile_open("/var/run/daemon.pid", 0600, &otherpid); 113if (pfh == NULL) { 114 if (errno == EEXIST) 115 errx(EXIT_FAILURE, "Daemon already running, pid: %d.", otherpid); 116 /* If we cannot create pidfile from other reasons, only warn. */ 117 warn("Cannot open or create pidfile"); 118} 119 120if (daemon(0, 0) == -1) { 121 warn("Cannot daemonize"); 122 pidfile_remove(pfh); 123 exit(EXIT_FAILURE); 124} 125 126pidfile_write(pfh); 127 128for (;;) { 129 /* Do work. */ 130 childpid = fork(); 131 switch (childpid) { 132 case -1: 133 syslog(LOG_ERR, "Cannot fork(): %s.", strerror(errno)); 134 break; 135 case 0: 136 pidfile_close(pfh); 137 /* Do child work. */ 138 break; 139 default: 140 syslog(LOG_INFO, "Child %d started.", childpid); 141 break; 142 } 143} 144 145pidfile_remove(pfh); 146exit(EXIT_SUCCESS); 147.Ed 148.Sh ERRORS 149The 150.Fn pidfile_open 151function will fail if: 152.Bl -tag -width Er 153.It Bq Er EEXIST 154Some process already holds the lock on the given pidfile, meaning that a 155daemon is already running. 156.It Bq Er ENAMETOOLONG 157Specified pidfile's name is too long. 158.It Bq Er EINVAL 159Some process already holds the lock on the given pidfile, but PID read 160from there is invalid. 161.El 162.Pp 163The 164.Fn pidfile_open 165function may also fail and set 166.Va errno 167for any errors specified for the 168.Xr fstat 2 , 169.Xr open 2 , 170and 171.Xr read 2 172calls. 173.Pp 174The 175.Fn pidfile_write 176function will fail if: 177.Bl -tag -width Er 178.It Bq Er EDOOFUS 179Improper function use. 180Probably called before 181.Fn pidfile_open . 182.El 183.Pp 184The 185.Fn pidfile_write 186function may also fail and set 187.Va errno 188for any errors specified for the 189.Xr fstat 2 , 190.Xr ftruncate 2 , 191and 192.Xr write 2 193calls. 194.Pp 195The 196.Fn pidfile_close 197function may fail and set 198.Va errno 199for any errors specified for the 200.Xr close 2 201and 202.Xr fstat 2 203calls. 204.Pp 205The 206.Fn pidfile_remove 207function will fail if: 208.Bl -tag -width Er 209.It Bq Er EDOOFUS 210Improper function use. 211Probably called not from the process which made 212.Fn pidfile_write . 213.El 214.Pp 215The 216.Fn pidfile_remove 217function may also fail and set 218.Va errno 219for any errors specified for the 220.Xr close 2 , 221.Xr flock 2 , 222.Xr fstat 2 , 223.Xr write 2 , 224and 225.Xr unlink 2 226calls. 227.Sh SEE ALSO 228.Xr flock 2 , 229.Xr open 2 , 230.Xr daemon 3 231.Sh AUTHORS 232.An -nosplit 233The 234.Nm pidfile 235functionality is based on ideas from 236.An John-Mark Gurney Aq jmg@FreeBSD.org . 237.Pp 238The code and manual page was written by 239.An Pawel Jakub Dawidek Aq pjd@FreeBSD.org . 240