Re: [Dmtcp-forum] What happens to standard error and standard ouput of programs run under DMTCP

[siavash m. <smi...@gm...>]

Thanks Gene for the quick reply.

I think I figured out why I was confused. When I redirect stderr and stdout
of myprogram to files, the output does not get flushed right away. In fact,
it gets flushed only after the program stops running (I am not quite sure
why it doesn't flush more often). Previously I was terminating myprogram
midway through. The reason the errfile and outfile files were empty was
because they were not flushed yet. If I wait until the program finishes,
standard error and standard output do get correctly redirected to errfile
and outfile.

Here is another question though. When I try to restart a program that has
redirected input and output, I get the following error:

[23713] ERROR at connection.cpp:1054 in restore;
REASON='JASSERT(jalib::Filesystem::FileExists(_path) == false) failed'
     _path = <dir>/errfile

where errfile is the file to which standard error was redirected. I am
guessing I need to manually remove errfile before restarting the program?

When I do manually remove the file and restart, everything seems to work ok,
but I get the following message:
[31218] NOTE at connection.cpp:1172 in restoreFile; REASON='File not
present, copying from saved checkpointed file'
     _path = <dir>/errfile

Just wondering if manually removing the standard output and error files and
ignoring the above note is the right thing to do?


Thanks
Siavash

On Fri, Jul 29, 2011 at 1:24 PM, Gene Cooperman <ge...@cc...> wrote:

> First, a little background on DMTCP, to see if I can clarify the question.
> The program dmtcp_checkpoint really just does an exec() into myprogram.
> There is always just one process (one pid).  Redirection of stdout and
> stderr survive across an exec().  In essence, dmtcp_checkpoint
> is a thin wrapper that does something close to:
>  LD_PRELOAD=dmtcphijack.so myprogram
> (assuming bash, where this will set LD_PRELOAD in the environment of
> myprogram)
>
> Next, you write:
> > everything (stderr of dmtcp_checkpoint in addition to stderr and stdout
> of
> > myprogram) is outputted to my screen, as expected.
>
> So, in the case below, that single stdout and stderr is redirected
> to outfile and errfile for both programs (since they're the same process).
> > dmtcp_checkpoint myprogram >outfile 2>errfile
>
> Essentially, the steps are:
> 1. The shell sets up the redirection
> 2. dmtcp_checkpoint begins
> 3. It execs into myprogram, while preserving the original redirection
>
> If you're interested in having DMTCP be less verbose, you could
> always try:  dmtcp_checkpoint --quiet myprogram
> (In general, dmtcp_checkpoint --help     for the options.)
>
> It's possible I misunderstood your question.  Does this help clarify
> things?
> If not, please write back.
>
> Best,
> - the DMTCP team
>
> On Fri, Jul 29, 2011 at 11:57:46AM -0500, siavash mirarab wrote:
> > Hello,
> >
> > I am wondering what happens to the standard error and standard output of
> the
> > program being run under dmtcp_checkpoint? Here is what I have
> > experienced. When I run
> >
> > dmtcp_checkpoint myprogram
> >
> > everything (stderr of dmtcp_checkpoint in addition to stderr and stdout
> of
> > myprogram) is outputted to my screen, as expected. However, when I run
> >
> > dmtcp_checkpoint myprogram >outfile 2>errfile
> >
> > only stderr and stdout of dmtcp_ckeckpoint seem to be redirected to
> errfile
> > and outfile (and outfile is empty).
> >
> > Is this the expected behavior? Is there a way to ask dmtcp_checkpoint to
> > redirect the stderr and stdout of myprogram to a file?
> >
> > Thanks
> > Siavash
>
> >
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