Hi, Based on a paper I read about giving an MPI job some fault tolerance, I'm exclusively connecting my processes with inter-communicators. I've found that if I increase the number of processes beyond a certain point, many processes don't get created at all and the whole job crashes. Am I running up against an operating system limit (like the number of open file descriptors - it is set at 1024), or some sort of MPICH limit? If it matters, my process architecture (a tree) is as follows: one master process connected to 21 manager processes on 21 other nodes, and each manager connected to 8 worker processes on the manager's own node. This is the largest job I've been able to create without it crashing. Attempting to increase the number of workers beyond 8 results in a crash. I'm using MPICH 3.3.2 on Centos 3.10.0. MPICH was compiled with the Portland Group compiler pgc++ 19.5-0. Thanks, Kurt