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298 lines
6.6 KiB
Groff
298 lines
6.6 KiB
Groff
.\" Copyright (c) 2005 Pawel Jakub Dawidek <pjd@FreeBSD.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd February 8, 2012
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.Dt PIDFILE 3
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.Os
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.Sh NAME
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.Nm pidfile_open ,
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.Nm pidfile_write ,
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.Nm pidfile_close ,
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.Nm pidfile_remove
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.Nd "library for PID files handling"
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.Sh LIBRARY
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.Lb libutil
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.Sh SYNOPSIS
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.In libutil.h
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.Ft "struct pidfh *"
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.Fn pidfile_open "const char *path" "mode_t mode" "pid_t *pidptr"
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.Ft int
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.Fn pidfile_write "struct pidfh *pfh"
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.Ft int
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.Fn pidfile_close "struct pidfh *pfh"
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.Ft int
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.Fn pidfile_remove "struct pidfh *pfh"
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.Ft int
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.Fn pidfile_fileno "struct pidfh *pfh"
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.Sh DESCRIPTION
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The
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.Nm pidfile
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family of functions allows daemons to handle PID files.
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It uses
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.Xr flopen 3
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to lock a pidfile and detect already running daemons.
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.Pp
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The
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.Fn pidfile_open
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function opens (or creates) a file specified by the
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.Fa path
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argument and locks it.
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If
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.Fa pidptr
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argument is not
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.Dv NULL
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and file can not be locked, the function will use it to store a PID of an
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already running daemon or
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.Li -1
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in case daemon did not write its PID yet.
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The function does not write process' PID into the file here, so it can be
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used before
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.Fn fork Ns ing
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and exit with a proper error message when needed.
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If the
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.Fa path
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argument is
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.Dv NULL ,
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.Pa /var/run/ Ns Ao Va progname Ac Ns Pa .pid
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file will be used.
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The
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.Fn pidfile_open
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function sets the O_CLOEXEC close-on-exec flag when opening the pidfile.
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.Pp
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The
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.Fn pidfile_write
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function writes process' PID into a previously opened file.
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The file is truncated before write, so calling the
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.Fn pidfile_write
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function multiple times is supported.
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.Pp
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The
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.Fn pidfile_close
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function closes a pidfile.
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It should be used after daemon
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.Fn fork Ns s
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to start a child process.
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.Pp
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The
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.Fn pidfile_remove
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function closes and removes a pidfile.
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.Pp
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The
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.Fn pidfile_fileno
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function returns the file descriptor for the open pidfile.
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.Sh RETURN VALUES
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The
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.Fn pidfile_open
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function returns a valid pointer to a
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.Vt pidfh
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structure on success, or
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.Dv NULL
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if an error occurs.
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If an error occurs,
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.Va errno
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will be set.
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.Pp
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.Rv -std pidfile_write pidfile_close pidfile_remove
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.Pp
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The
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.Fn pidfile_fileno
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function returns the low-level file descriptor.
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It returns
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.Li -1
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and sets
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.Va errno
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if a NULL
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.Vt pidfh
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is specified, or if the pidfile is no longer open.
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.Sh EXAMPLES
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The following example shows in which order these functions should be used.
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Note that it is safe to pass
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.Dv NULL
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to
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.Fn pidfile_write ,
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.Fn pidfile_remove ,
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.Fn pidfile_close
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and
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.Fn pidfile_fileno
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functions.
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.Bd -literal
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struct pidfh *pfh;
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pid_t otherpid, childpid;
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pfh = pidfile_open("/var/run/daemon.pid", 0600, &otherpid);
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if (pfh == NULL) {
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if (errno == EEXIST) {
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errx(EXIT_FAILURE, "Daemon already running, pid: %jd.",
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(intmax_t)otherpid);
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}
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/* If we cannot create pidfile from other reasons, only warn. */
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warn("Cannot open or create pidfile");
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/*
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* Eventhough pfh is NULL we can continue, as the other pidfile_*
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* function can handle such situation by doing nothing except setting
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* errno to EDOOFUS.
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*/
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}
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if (daemon(0, 0) == -1) {
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warn("Cannot daemonize");
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pidfile_remove(pfh);
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exit(EXIT_FAILURE);
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}
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pidfile_write(pfh);
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for (;;) {
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/* Do work. */
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childpid = fork();
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switch (childpid) {
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case -1:
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syslog(LOG_ERR, "Cannot fork(): %s.", strerror(errno));
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break;
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case 0:
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pidfile_close(pfh);
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/* Do child work. */
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break;
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default:
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syslog(LOG_INFO, "Child %jd started.", (intmax_t)childpid);
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break;
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}
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}
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pidfile_remove(pfh);
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exit(EXIT_SUCCESS);
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.Ed
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.Sh ERRORS
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The
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.Fn pidfile_open
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function will fail if:
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.Bl -tag -width Er
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.It Bq Er EEXIST
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Some process already holds the lock on the given pidfile, meaning that a
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daemon is already running.
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If
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.Fa pidptr
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argument is not
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.Dv NULL
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the function will use it to store a PID of an already running daemon or
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.Li -1
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in case daemon did not write its PID yet.
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.It Bq Er ENAMETOOLONG
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Specified pidfile's name is too long.
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.It Bq Er EINVAL
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Some process already holds the lock on the given pidfile, but PID read
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from there is invalid.
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.El
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.Pp
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The
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.Fn pidfile_open
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function may also fail and set
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.Va errno
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for any errors specified for the
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.Xr fstat 2 ,
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.Xr open 2 ,
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and
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.Xr read 2
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calls.
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.Pp
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The
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.Fn pidfile_write
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function will fail if:
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.Bl -tag -width Er
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.It Bq Er EDOOFUS
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Improper function use.
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Probably called before
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.Fn pidfile_open .
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.El
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.Pp
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The
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.Fn pidfile_write
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function may also fail and set
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.Va errno
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for any errors specified for the
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.Xr fstat 2 ,
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.Xr ftruncate 2 ,
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and
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.Xr write 2
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calls.
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.Pp
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The
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.Fn pidfile_close
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function may fail and set
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.Va errno
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for any errors specified for the
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.Xr close 2
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and
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.Xr fstat 2
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calls.
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.Pp
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The
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.Fn pidfile_remove
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function will fail if:
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.Bl -tag -width Er
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.It Bq Er EDOOFUS
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Improper function use.
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Probably called not from the process which made
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.Fn pidfile_write .
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.El
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.Pp
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The
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.Fn pidfile_remove
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function may also fail and set
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.Va errno
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for any errors specified for the
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.Xr close 2 ,
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.Xr fstat 2 ,
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.Xr write 2 ,
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and
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.Xr unlink 2
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system calls and the
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.Xr flopen 3
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library function.
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.Pp
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The
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.Fn pidfile_fileno
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function will fail if:
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.Bl -tag -width Er
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.It Bq Er EDOOFUS
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Improper function use.
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Probably called not from the process which used
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.Fn pidfile_open .
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.El
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.Sh SEE ALSO
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.Xr open 2 ,
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.Xr daemon 3 ,
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.Xr flopen 3
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.Sh AUTHORS
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.An -nosplit
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The
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.Nm pidfile
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functionality is based on ideas from
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.An John-Mark Gurney Aq Mt jmg@FreeBSD.org .
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.Pp
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The code and manual page was written by
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.An Pawel Jakub Dawidek Aq Mt pjd@FreeBSD.org .
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