[mpich-discuss] Hydra WARNING: too many ssh connections
zhouh at anl.gov
Fri Apr 1 16:19:32 CDT 2022
Every time you call MPI_Comm_spawn, hydra will launch a ssh (for each host) to create a proxy. It is certainly not ideal for applications relying on spawning many processes.
From: Mccall, Kurt E. (MSFC-EV41) via discuss <discuss at mpich.org>
Sent: Friday, April 1, 2022 4:08 PM
To: discuss at mpich.org <discuss at mpich.org>
Cc: Mccall, Kurt E. (MSFC-EV41) <kurt.e.mccall at nasa.gov>
Subject: [mpich-discuss] Hydra WARNING: too many ssh connections
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
I’m calling mpiexec with the “—launcher ssh” option, MPICH 4.0.1.
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