freebsd-dev/lib/libutil/pidfile.3

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.\" Copyright (c) 2005 Pawel Jakub Dawidek <pjd@FreeBSD.org>
.\" All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" $FreeBSD$
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.Dd August 22, 2005
.Dt PIDFILE 3
.Os
.Sh NAME
.Nm pidfile_open ,
.Nm pidfile_write ,
.Nm pidfile_close ,
.Nm pidfile_remove
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.Nd "library for PID files handling"
.Sh LIBRARY
.Lb libutil
.Sh SYNOPSIS
.In sys/param.h
.In libutil.h
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.Ft "struct pidfh *"
.Fn pidfile_open "const char *path" "mode_t mode" "pid_t *pidptr"
.Ft int
.Fn pidfile_write "struct pidfh *pfh"
.Ft int
.Fn pidfile_close "struct pidfh *pfh"
.Ft int
.Fn pidfile_remove "struct pidfh *pfh"
.Sh DESCRIPTION
The
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.Nm pidfile
family of functions allows daemons to handle PID files.
It uses
.Xr flock 2
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to lock a pidfile and detect already running daemons.
.Pp
The
.Fn pidfile_open
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function opens (or creates) a file specified by the
.Fa path
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argument and locks it with the
.Xr flock 2
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system call.
If a file can not be locked, a PID of an already running daemon is returned in
the
.Fa pidptr
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argument (if it is not
.Dv NULL ) .
The function does not write process' PID into the file here, so it can be
used before
.Fn fork Ns ing
and exit with a proper error message when needed.
If the
.Fa path
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argument is
.Dv NULL ,
.Pa /var/run/ Ns Ao Va progname Ac Ns Pa .pid
file will be used.
.Pp
The
.Fn pidfile_write
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function writes process' PID into a previously opened file.
.Pp
The
.Fn pidfile_close
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function closes a pidfile.
It should be used after daemon
.Fn fork Ns s
to start a child process.
.Pp
The
.Fn pidfile_remove
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function closes and removes a pidfile.
.Sh RETURN VALUES
The
.Fn pidfile_open
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function returns a valid pointer to a
.Vt pidfh
structure on success, or
.Dv NULL
if an error occurs.
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If an error occurs,
.Va errno
will be set.
.Rv -std pidfile_write pidfile_close pidfile_remove
.Sh EXAMPLES
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The following example shows in which order these functions should be used.
Note that it is safe to pass
.Dv NULL
to
.Fn pidfile_write ,
.Fn pidfile_remove
and
.Fn pidfile_close
functions.
.Bd -literal
struct pidfh *pfh;
pid_t otherpid, childpid;
pfh = pidfile_open("/var/run/daemon.pid", 0600, &otherpid);
if (pfh == NULL) {
if (errno == EEXIST) {
errx(EXIT_FAILURE, "Daemon already running, pid: %jd.",
(intmax_t)otherpid);
}
/* If we cannot create pidfile from other reasons, only warn. */
warn("Cannot open or create pidfile");
}
if (daemon(0, 0) == -1) {
warn("Cannot daemonize");
pidfile_remove(pfh);
exit(EXIT_FAILURE);
}
pidfile_write(pfh);
for (;;) {
/* Do work. */
childpid = fork();
switch (childpid) {
case -1:
syslog(LOG_ERR, "Cannot fork(): %s.", strerror(errno));
break;
case 0:
pidfile_close(pfh);
/* Do child work. */
break;
default:
syslog(LOG_INFO, "Child %jd started.", (intmax_t)childpid);
break;
}
}
pidfile_remove(pfh);
exit(EXIT_SUCCESS);
.Ed
.Sh ERRORS
The
.Fn pidfile_open
function will fail if:
.Bl -tag -width Er
.It Bq Er EEXIST
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Some process already holds the lock on the given pidfile, meaning that a
daemon is already running.
.It Bq Er ENAMETOOLONG
Specified pidfile's name is too long.
.It Bq Er EINVAL
Some process already holds the lock on the given pidfile, but PID read
from there is invalid.
.El
.Pp
The
.Fn pidfile_open
function may also fail and set
.Va errno
for any errors specified for the
.Xr fstat 2 ,
.Xr open 2 ,
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and
.Xr read 2
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calls.
.Pp
The
.Fn pidfile_write
function will fail if:
.Bl -tag -width Er
.It Bq Er EDOOFUS
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Improper function use.
Probably called before
.Fn pidfile_open .
.El
.Pp
The
.Fn pidfile_write
function may also fail and set
.Va errno
for any errors specified for the
.Xr fstat 2 ,
.Xr ftruncate 2 ,
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and
.Xr write 2
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calls.
.Pp
The
.Fn pidfile_close
function may fail and set
.Va errno
for any errors specified for the
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.Xr close 2
and
.Xr fstat 2
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calls.
.Pp
The
.Fn pidfile_remove
function will fail if:
.Bl -tag -width Er
.It Bq Er EDOOFUS
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Improper function use.
Probably called not from the process which made
.Fn pidfile_write .
.El
.Pp
The
.Fn pidfile_remove
function may also fail and set
.Va errno
for any errors specified for the
.Xr close 2 ,
.Xr flock 2 ,
.Xr fstat 2 ,
.Xr write 2 ,
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and
.Xr unlink 2
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calls.
.Sh SEE ALSO
.Xr flock 2 ,
.Xr open 2 ,
.Xr daemon 3
.Sh AUTHORS
.An -nosplit
The
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.Nm pidfile
functionality is based on ideas from
.An John-Mark Gurney Aq jmg@FreeBSD.org .
.Pp
The code and manual page was written by
.An Pawel Jakub Dawidek Aq pjd@FreeBSD.org .