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Strange EPERM in mpich node on diskless cluster


I have an MPI program which does a popen and fread, something like:

      if (snprintf (filename, 999, "gunzip -c < %s.cpu%.4d.data",
		    basename, rank) > 999)
	return 1;
      if (!(infile = popen (filename, "r")))
	return 1;
      if (ferror (infile))
	  printf ("[%d] Pipe open has error %d\n", rank, ferror(infile));
	  fflush (stdout);
      ... some stuff ...
	nmemb=fread (globalarray, sizeof (PetscScalar), gridpoints * dof, infile);
	if (nmemb != gridpoints*dof)
	    printf ("[%d] ferror = %d\n", rank, ferror (infile));
	    fflush (stdout);

So, there seems to be no error in the popen, but on one cluster, on
between one and five CPUs, the fread results in an EPERM error.  On the
other cluster, no such error.  They're both identically-configured
Debian beowulfs using the diskless package and mpich, though the one
with no errors is made of dual AthlonXP 1.53 GHz boxes and the one with
errors of dual Opteron 240 boxes.

On the other hand, the same program earlier fopen()s a file whose path
and name are identical to the popen redirected input except for the
extension, and those work flawlessly.

machines.LINUX on the starting node (say node2) in both cases looks
something like:

Any ideas on what could be going wrong, or how to debug this?


-Adam P.

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