errors when running multiple openssh sessions

Dan Kaminsky dan at
Tue Jun 17 06:08:59 EST 2003

jcduell at wrote:

>Openssh seems to fail sporadically if you issue lots of simultaneous
>ssh commands, at least under certain conditions.  Take the following
>    #!/bin/sh
>    for NUM in 0 1 2 3 4 5 6 7 8 9; do 
>        ssh n2003 echo $NUM "$*" &
>    done
>So, we're running 10 ssh commands at once.  
>When I run this program once, all 
>I've observed this bug on OpenSSH_3.6.1p1 on Tru64, OpenSSH 3.2.3p1 on
>an IBM SP, and on OpenSSH 3.5p1-6 on Redhat Linux 9. So I suspect it's a
>general problem.
That invocation creates quite a spike in CPU usage.  Who knows, it might 
also be causing headaches for privsep.  A better way to do what you 
describe above would be this:


for NUM in 0 1 2 3 4 5 6 7 8 9; do
        echo $NUM "$*" \&
done | ssh n2003

 From what I've found, this is the best way to execute sets of commands 
remotely without significant CPU load.  You do lose all sorts of 
conveniences -- error codes, the ability to distinguish between the 
results of several commands, standard syntax for specifying shell -- but 
you're losing most of that from parallel execution anyway, and this is 
really quite fast.

Of course, ssh shouldn't crash no matter what.  But this might be of use 


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