[K12OSN] ssh issue with LDM

Jim Kinney jim.kinney at gmail.com
Thu Dec 15 03:08:13 UTC 2011

ssh does a reverse lookup to try and identify the far end of the
connection. If the remote end doesn't resolve by a dns lookup, things get
very, very slow. You can have an /etc/hosts file be sufficient as long as
the /etc/nsswitch file is set to try hosts firsts (default).

The TCs don't have a populated hosts file so they rely on DNS.

Unless you supply a hosts file from the servers supply side /etc area for
the TCs.

On Wed, Dec 14, 2011 at 7:05 PM, David Hopkins <dahopkins429 at gmail.com>wrote:

> All,
> I am beginning to suspect this issue is because ssh isn't resolving
> names correctly?  Timing
> ssh myserver
> from a shell (ALT-CTL-F2) takes about 30 seconds to resolve myserver.
> However, ssh any_other_server returns immediately.  So, why wouldn't
> myserver resolve quickly?  This is true from any of the servers ..
> they do not resolve their names quickly.  On all of them, the local
> (thin client) /etc/hosts has the form
> localhost
> ltsp50
> server
> where the thin client is lstp50 ... but ... server is not defined in
> DNS, only in the thin clients /etc/hosts.  Logging in at the console
> for any account also works.
> This is very very very confusing and unfortunately, come tomorrow
> morning is going to be a major issue.
> Sincerely,
> Dave Hopkins
> On Wed, Dec 14, 2011 at 6:13 PM, David Hopkins <dahopkins429 at gmail.com>
> wrote:
> > We are having a major issue with thin client authentication. It
> > started just after lunch time today. Authentication works fine from
> > console and on terminal, but ssh takes a very long time to connect.
> > One server (out of 5) can still connect though the login process takes
> > quite a while to complete.  However, it is shorter than the other
> > servers, so we suspect it is a timeout issue with LDM.
> >
> > From a shell at the thin client I can ssh to any system and
> > authenticate.  However, trying to ssh from a shell at the client to
> > the ltsp server that the client is connected to takes a very long
> > time.  The response at the GUI login screen is "no response from
> > server, restarting". We have already updated the sshkeys and
> > completely rebuilt the image but this hasn't resolved the issue. How
> > does LDM use ssh for authentication? Is there a reason ssh would have
> > to be routed?  And .. why would ssh to any system except the system
> > that the client booted from take so long?  We have enabled
> > IP_Forwarding at the clients for localapps and that also works if that
> > information is of any use.
> >
> > Any help is greatly appreciated!
> >
> > Sincerely,
> > Dave Hopkins
> _______________________________________________
> K12OSN mailing list
> K12OSN at redhat.com
> https://www.redhat.com/mailman/listinfo/k12osn
> For more info see <http://www.k12os.org>

James P. Kinney III

As long as the general population is passive, apathetic, diverted to
consumerism or hatred of the vulnerable, then the powerful can do as they
please, and those who survive will be left to contemplate the outcome.
- *2011 Noam Chomsky

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listman.redhat.com/archives/k12osn/attachments/20111214/70d79d8f/attachment.htm>

More information about the K12OSN mailing list