'\"macro stdmacro
.\"
.\" Copyright (c) 2000-2004 Silicon Graphics, Inc.  All Rights Reserved.
.\" 
.\" This program is free software; you can redistribute it and/or modify it
.\" under the terms of the GNU General Public License as published by the
.\" Free Software Foundation; either version 2 of the License, or (at your
.\" option) any later version.
.\" 
.\" This program is distributed in the hope that it will be useful, but
.\" WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
.\" or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
.\" for more details.
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.\"
.TH PMOPENLOG 3 "PCP" "Performance Co-Pilot"
.SH NAME
\f3pmOpenLog\f1 \- create a log file for diagnostics and debug output
.SH "C SYNOPSIS"
.ft 3
#include <pcp/pmapi.h>
.sp
.ad l
.hy 0
.in +8n
.ti -8n
FILE *pmOpenLog(const char *\fIprogname\fP, const char *\fIlogname\fP, FILE\ *\fIoldstream\fP, int\ *\fIstatus\fP);
.sp
.in
.hy
.ad
cc ... \-lpcp
.ft 1
.SH DESCRIPTION
.B pmOpenLog
reassigns the standard I/O stream
.I oldstream
(normally
.BR stderr )
to be associated with the file
.IR logname .
If
.I logname
is not \fB"-"\fP
and already exists,
it will be removed and recreated if possible (to ensure correct ownership
and permissions from the caller to
.BR pmOpenLog ).
.PP
As a special case, if
.I logname
is "\fB-\fR"
then no removal or reopening is performed and
the function simply sets
.I status
to
.B 1
and returns
.IR oldstream .
This is useful when the caller wants diagnostics on
.I oldstream
stream (normally
.BR stderr )
rather than a file, e.g.
.B "pmlogger -l-"
or
.BR "pmcd -f -l-" .
Logging to
.B stderr
is also useful for PMDAs in a containerized environment where
it is beneficial for all PMDA logs to be written to
.BR pmcd 's
.B stderr
stream (and thus to a single destination), whether that is a file such as
.B pmcd.log
or the original 
stream inherited from the shell.
.PP
On return, the function value is the standard I/O stream, possibly replacing
.IR oldstream .
In the
event of an error, the return value will be
.I oldstream
unchanged and
.I status
will be
.BR 0 .
.PP
For success,
.I status
is
.BR 1 ,
and a standard preamble is written to
.I logname
.ti +0.5i
.ft B
Log for \fIprogname\fB on \fIhostname\fB started \fIdate and time\fB
.ft R
.br
and an
.BR atexit (3)
handler is installed to write the postscript message to
.I logname
.ti +0.5i
.ft B
Log finished \fIdate and time\fB
.ft R
.br
when the processes exits.
.PP
.I progname
is only used to annotate messages.
.SH SEE ALSO
.BR atexit (3)
and
.BR freopen (3).