Hi,  you provided the following information about the warning “too many ssh connections”:

The particular warning is issued by hydra, MPICH’s process manager. Following excerpt is the comment in that source code:

        /* ssh has many types of security controls that do not allow a

         * user to ssh to the same node multiple times very

         * quickly. If this happens, the ssh daemons disables ssh

         * connections causing the job to fail. This is basically a

         * hack to slow down ssh connections to the same node. We

         * check for offset == 0 before applying this hack, so we only

         * slow down the cases where ssh is being used, and not the

         * cases where we fall back to fork. */

Is this just during an initial ssh connection attempt?  I’m trying to figure out where my code is triggering this warning.  Could it be from

1. MPI_Intercomm_create
2. MPI_Comm_spawn
3. others?

I’m calling mpiexec with the “—launcher ssh” option, MPICH 4.0.1.

Thanks,

Kurt