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Re: Using pre-existing SSH connection

From: Joe Sapp
Subject: Re: Using pre-existing SSH connection
Date: Thu, 11 May 2017 19:54:50 -0400

On Thu, May 11, 2017 at 6:24 PM, Ole Tange <address@hidden> wrote:
> On Mon, May 8, 2017 at 10:20 PM, Joe Sapp <address@hidden> wrote:
>> On Mon, May 8, 2017 at 4:09 PM, Ole Tange <address@hidden> wrote:
>>> On Mon, May 8, 2017 at 9:02 PM, Joe Sapp <address@hidden> wrote:
> :
>> I am using --controlmaster in my calls to parallel, but it seems to
>> still be making new connections even though I don't have a custom ssh
>> command.  I will try to come up with a test case and some evidence.
> GNU Parallel starts a 'ssh -MTS socket' which is kept open for the whole time:

Oh okay, this makes sense now.  I just did some testing after reading
the ssh ControlMaster section a bit closer and opening up a master ssh
session to $SERVER:

  seq 5 | parallel --sshlogin $SERVER --ssh "ssh -v" echo

The output showed the following after each echo, indicating that it
used multiplexing:

  debug1: mux_client_request_session: master session id: 2

The problem was twofold: I had enabled ssh ControlMaster globally, so
all of my ssh sessions were creating new master sessions.  Once that
was resolved, I could see that using the "--controlmaster" option of
GNU Parallel was creating a new master session as well (as you point
out).  If I just omit the option it will re-use my existing master
session as expected.


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