174 lines
4.7 KiB
Groff
174 lines
4.7 KiB
Groff
.\" $NetBSD: pidfile.3,v 1.16 2017/10/22 16:55:32 abhinav Exp $
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.\"
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.\" Copyright (c) 1999, 2016 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Jason R. Thorpe and Roy Marples.
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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 NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd April 10, 2016
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.Dt PIDFILE 3
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.Os
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.Sh NAME
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.Nm pidfile ,
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.Nm pidfile_lock ,
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.Nm pidfile_read ,
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.Nm pidfile_clean
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.Nd write a daemon pid file
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.Sh LIBRARY
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.Lb libutil
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.Sh SYNOPSIS
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.In util.h
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.Ft int
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.Fn pidfile "const char *path"
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.Ft pid_t
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.Fn pidfile_lock "const char *path"
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.Ft pid_t
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.Fn pidfile_read "const char *path"
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.Ft int
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.Fn pidfile_clean "void"
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.Sh DESCRIPTION
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.Fn pidfile
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and
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.Fn pidfile_lock
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create and lock a file containing the process ID of the calling program.
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The pid file can be used as a quick reference if
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the process needs to be sent a signal.
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The pid file is truncated and removed automatically when the program exits,
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unless the program receives a fatal signal.
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.Pp
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If
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.Ar path
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is
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.Dv NULL
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or a plain basename (a name containing no directory components), the pid file
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is created in the
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.Pa /var/run
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directory.
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The file name has the form
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.Pa /var/run/basename.pid .
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The basename part is either the value of
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.Ar path
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if it was not
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.Dv NULL ,
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or the program name as returned by
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.Xr getprogname 3
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otherwise.
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.Pp
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If
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.Ar path
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is an absolute or relative path (i.e. it contains the
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.Sq /
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character),
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the pid file is created in the provided location.
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.Pp
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If called with a new
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.Ar path ,
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.Fn pidfile
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and
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.Fn pidfile_lock
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will remove the old pid file.
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.Pp
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The pid file is truncated, so these functions can be called multiple times and
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allow a child process to take over the lock.
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.Pp
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.Fn pidfile_read
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will read the last pid file created, or specified by
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.Ar path ,
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and return the process ID it contains.
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.Pp
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.Fn pidfile_clean
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will
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.Xr ftruncate 2 ,
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.Xr close 2 ,
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and
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.Xr unlink 2
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the last opening pid file if, and only if, the current process wrote it.
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This function should be called if the program needs to call
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.Xr _exit 2
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(such as from a signal handler) and needs to clean up the pid file.
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.Sh RETURN VALUES
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.Fn pidfile
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and
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.Fn pidfile_clean
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returns 0 on success and \-1 on failure.
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.Pp
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.Fn pidfile_lock
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returns 0 on success.
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Otherwise, the process ID who owns the lock is returned and if that
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cannot be derived then \-1 is returned.
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.Pp
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.Fn pidfile_read
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returns the process ID if known, otherwise \-1.
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.Sh ERRORS
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The
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.Fn pidfile
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and
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.Fn pidfile_lock
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functions 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 pid file, meaning that a
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daemon is already running.
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.It Bq Er ENAMETOOLONG
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Specified pidfile's name is too long.
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.El
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.Sh SEE ALSO
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.Xr flock 2 ,
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.Xr atexit 3
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.Sh HISTORY
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The
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.Fn pidfile
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function call appeared in
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.Nx 1.5 .
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Support for creating pid files in any arbitrary path was added in
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.Nx 6.0 .
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.Pp
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The
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.Fn pidfile_lock ,
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.Fn pidfile_read ,
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and
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.Fn pidfile_clean
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function calls appeared in
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.Nx 8 .
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.Sh CAVEATS
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.Fn pidfile
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and
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.Fn pidfile_lock
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use
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.Xr atexit 3
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to ensure the pid file is cleaned at program exit.
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However, programs that use the
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.Xr _exit 2
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function (for example, in signal handlers)
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will not trigger this behaviour and should call
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.Fn pidfile_clean .
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Like-wise, if the program creates a pid file before
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.Xr fork 2 Ns ing
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a child to take over, it should use the
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.Xr _exit 2
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function instead of returning or using the
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.Xr exit 3
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function to ensure the pid file is not cleaned.
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