libvirt users - Feb 2022 - qemu+ssh connections to a remote libvirt fail as ssh banner configured

Thank you! I tried /etc/motd, and it does not impact the libvirt connection.
Happy to learn something new!

On Thu, Feb 10, 2022 at 4:50 PM Daniel P. Berrang? <berrange at
redhat.com>
wrote:
> On Thu, Feb 10, 2022 at 09:33:38AM +0100, Michal Pr?vozn?k wrote:
> > On 2/10/22 09:02, Daniel P. Berrang? wrote:
> > > On Thu, Feb 10, 2022 at 09:52:52AM +0800, Yalan Zhang wrote:
> > >> Hi there,
> > >>
> > >> I have a system configured with ssh login banner like as
below:
> > >> # cat ~/.bashrc
> > >> ...
> > >> echo
> > >>
>
"================================================================================="
> > >> echo "====== This machine is occupied by xxx for testing
now. If you
> are
> > >> about to use it, contact xxx first ======"
> > >> echo
> > >>
>
"================================================================================="
> > >>
> > >> It works as expected that whenever someone logs into this
system by
> ssh,
> > >> he/she will see this warning message.
> > >> But it seems such settings will impact a virsh client
connection with
> ssh,
> > >> when I try to connect the libvirt daemon on this system, it
will
> error out :
> > >> # virsh -c qemu+ssh://${my_host}/system list --all
> > >> root@${my_host}'s password:
> > >> error: failed to connect to the hypervisor
> > >> error: packet 1027423545 bytes received from server too
large, want
> 33554432
> > >
> > > Libvirt is tunnelling an RPC protocol over the SSH connection.
> > > Your bashrc is printing this text onto the SSH conmnection and
> > > that corrupts the libvirt RPC protocol.
> > >
> > > If you want to print something whjen people login use the
> > > /etc/motd file which is designed for this pupose, don't
> > > print stuff from a .bashrc.  Libvirt gives the options to
> > > SSH that prevent display of /etc/motd contents, so that
> > > its RPC protocol doesn't get corrupted.
> >
> > One more thing, I wasn't able to reproduce when virt-ssh-helper
was
> > used. But maybe I wasn't trying hard enough.
>
> That should be affected in exactly the same way. It still relies on
> stdout/stdin being clean data channels.
>
> Regards,
> Daniel
> --
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>
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On Thu, Feb 10, 2022 at 17:47:43 +0800, Yalan Zhang
wrote:
> Thank you! I tried /etc/motd, and it does not impact the libvirt
connection.
> Happy to learn something new!
Alternatively if you really need to run commands in .bashrc which can
potentially print some output, you can put them after a check for
interactive shell:

    if [[ $- != *i* ]] ; then
        # Shell is non-interactive.  Be done now!
        return
    fi

    echo "Interactive shell here. How are you?"

Jirka