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 October 20, 2008 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 flopen 3 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. 62If a file can not be locked, a PID of an already running daemon is returned in 63the 64.Fa pidptr 65argument (if it is not 66.Dv NULL ) . 67The function does not write process' PID into the file here, so it can be 68used before 69.Fn fork Ns ing 70and exit with a proper error message when needed. 71If the 72.Fa path 73argument is 74.Dv NULL , 75.Pa /var/run/ Ns Ao Va progname Ac Ns Pa .pid 76file will be used. 77.Pp 78The 79.Fn pidfile_write 80function writes process' PID into a previously opened file. 81.Pp 82The 83.Fn pidfile_close 84function closes a pidfile. 85It should be used after daemon 86.Fn fork Ns s 87to start a child process. 88.Pp 89The 90.Fn pidfile_remove 91function closes and removes a pidfile. 92.Sh RETURN VALUES 93The 94.Fn pidfile_open 95function returns a valid pointer to a 96.Vt pidfh 97structure on success, or 98.Dv NULL 99if an error occurs. 100If an error occurs, 101.Va errno 102will be set. 103.Rv -std pidfile_write pidfile_close pidfile_remove 104.Sh EXAMPLES 105The following example shows in which order these functions should be used. 106Note that it is safe to pass 107.Dv NULL 108to 109.Fn pidfile_write , 110.Fn pidfile_remove 111and 112.Fn pidfile_close 113functions. 114.Bd -literal 115struct pidfh *pfh; 116pid_t otherpid, childpid; 117 118pfh = pidfile_open("/var/run/daemon.pid", 0600, &otherpid); 119if (pfh == NULL) { 120 if (errno == EEXIST) { 121 errx(EXIT_FAILURE, "Daemon already running, pid: %jd.", 122 (intmax_t)otherpid); 123 } 124 /* If we cannot create pidfile from other reasons, only warn. */ 125 warn("Cannot open or create pidfile"); 126} 127 128if (daemon(0, 0) == -1) { 129 warn("Cannot daemonize"); 130 pidfile_remove(pfh); 131 exit(EXIT_FAILURE); 132} 133 134pidfile_write(pfh); 135 136for (;;) { 137 /* Do work. */ 138 childpid = fork(); 139 switch (childpid) { 140 case -1: 141 syslog(LOG_ERR, "Cannot fork(): %s.", strerror(errno)); 142 break; 143 case 0: 144 pidfile_close(pfh); 145 /* Do child work. */ 146 break; 147 default: 148 syslog(LOG_INFO, "Child %jd started.", (intmax_t)childpid); 149 break; 150 } 151} 152 153pidfile_remove(pfh); 154exit(EXIT_SUCCESS); 155.Ed 156.Sh ERRORS 157The 158.Fn pidfile_open 159function will fail if: 160.Bl -tag -width Er 161.It Bq Er EEXIST 162Some process already holds the lock on the given pidfile, meaning that a 163daemon is already running. 164.It Bq Er ENAMETOOLONG 165Specified pidfile's name is too long. 166.It Bq Er EINVAL 167Some process already holds the lock on the given pidfile, but PID read 168from there is invalid. 169.It Bq Er EAGAIN 170Some process already holds the lock on the given pidfile, but the file 171is truncated. 172Most likely, the existing daemon is writing new PID into 173the file. 174.El 175.Pp 176The 177.Fn pidfile_open 178function may also fail and set 179.Va errno 180for any errors specified for the 181.Xr fstat 2 , 182.Xr open 2 , 183and 184.Xr read 2 185calls. 186.Pp 187The 188.Fn pidfile_write 189function will fail if: 190.Bl -tag -width Er 191.It Bq Er EDOOFUS 192Improper function use. 193Probably called before 194.Fn pidfile_open . 195.El 196.Pp 197The 198.Fn pidfile_write 199function may also fail and set 200.Va errno 201for any errors specified for the 202.Xr fstat 2 , 203.Xr ftruncate 2 , 204and 205.Xr write 2 206calls. 207.Pp 208The 209.Fn pidfile_close 210function may fail and set 211.Va errno 212for any errors specified for the 213.Xr close 2 214and 215.Xr fstat 2 216calls. 217.Pp 218The 219.Fn pidfile_remove 220function will fail if: 221.Bl -tag -width Er 222.It Bq Er EDOOFUS 223Improper function use. 224Probably called not from the process which made 225.Fn pidfile_write . 226.El 227.Pp 228The 229.Fn pidfile_remove 230function may also fail and set 231.Va errno 232for any errors specified for the 233.Xr close 2 , 234.Xr fstat 2 , 235.Xr write 2 , 236and 237.Xr unlink 2 238system calls and the 239.Xr flopen 3 240library function. 241.Sh SEE ALSO 242.Xr open 2 , 243.Xr daemon 3 , 244.Xr flopen 3 245.Sh AUTHORS 246.An -nosplit 247The 248.Nm pidfile 249functionality is based on ideas from 250.An John-Mark Gurney Aq jmg@FreeBSD.org . 251.Pp 252The code and manual page was written by 253.An Pawel Jakub Dawidek Aq pjd@FreeBSD.org . 254