Re: Help! 10.04 LTSP configuration using only one nic

Mike Biancaniello mikebianc at
Wed Sep 7 18:57:10 UTC 2011

sorry, forgot to reply-to-all ...

I'm not sure why you would need iptables if you only have a 1-nic server and fat clients.
I just recently migrated from a 2-nic to a 1-nic setup and the ltsp server is the DHCP server for the entire LAN,
which means I need to specify the MAC addrs that I want to LTSP and then all others by default are just returned the IP info.

 you only have 1 subnet on your one NIC, then as long as the LTSP dhcp
server returns network info that matches the server's own (not a second
network like in many of the examples), then you should be fine.

In this config, each ltsp client receives an IP on the main LAN.
LocalApps and fat clients can run without any forwarding or NAT or iptables magic from the server.

mike at ltsp-server:~$ cat /etc/network/interfaces
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static

mike at kidbuntu:~$ cat /etc/resolv.conf
# Generated by NetworkManager

mike at kidbuntu:~$ cat /etc/ltsp/dhcpd.conf
# Default LTSP dhcpd.conf config file.

;ddns-update-style interim
;update-static-leases on
;option domain-name-servers

;subnet netmask {
;  option broadcast-address
;  option routers
;  option subnet-mask

group {
  #  These are the hosts that are allowed to pxe-boot
  option root-path "/opt/ltsp/i386"
;  if substring( option vendor-class-identifier, 0, 9 ) = "PXEClient" {
    filename "/ltsp/i386/pxelinux.0"
;  } else {
    filename "/ltsp/i386/nbi.img"
;  }
  host kid1   { hardware ethernet 00:0d:56:8c:03:34;
    option host-name "kidputer1"
;    ddns-hostname "kidputer1";
  host kid2   { hardware ethernet 00:0d:56:a6:ff:f5;
    option host-name "kidputer2"
;    ddns-hostname "kidputer2";

From: Jim Christiansen <jim.c.christiansen at>
To: David Groos <djgroos at>
Cc: edubuntu-users <edubuntu-users at>
Sent: Wednesday, September 07, 2011 at 11:35 am
Subject: Re: Help! 10.04 LTSP configuration using only one nic

 morning, David.  Thank you for the help and any ideas.  My clients are
(year 2006) Dell GX620s with 3.6 ghz p4s and all with 1 gig ram.

 never used two nics in any of my other LTSP setups as I had always kept
 them behind IPCOP firewalls.  I haven't had to apply iptable rules for
years and really don't understand what the 1st history command, #49, is
doing.  There is no mention of eth0 or what ever.

I don't know who Alkis is, but is he running his setup on a 100 megabit lan?  Could the fat image be slimmed down I wonder?

 just talked to the VP and he says that money is tight to purchase gig
switches.  I had been thinking of yanking the 20 100 mbit switches and
swapping in new gig switches.

I'll be in a pickle here pretty soon.  Thanks again,  Jim

On Wed, Sep 7, 2011 at 8:14 AM, David Groos <djgroos at> wrote:

 hardware are your fat clients running on?  Is there a difference in RAM
 between the good and poorly functioning clients?  I've seen these
symptoms before I upgraded the RAM on all my (Pentium 4's, 2.4-2.8 GHz)
fat clients to 1 gig.

Alkis insists that a regular PC (with sufficient RAM) works well as
the LTSP server IF you are using fat clients.  In his labs the teachers
actually uses the server as their classroom PC!  Makes the whole thing
more affordable and practical.

Do you mind sharing why you chose to use a single NIC setup? 

Good luck,
David G

On Tue, Sep 6, 2011 at 3:45 PM, Jim Christiansen <jim.c.christiansen at> wrote:


 just had an aging server fail to start up and need to get to the bottom
 of another problem on another new server running Ubuntu 10.04 LTSP
before attempting to do another install.  We lost one server in the
Library late last June- rgreat timing and another one just today that
served my classroom has failed to start up-  Both are 5 years or older.

My old Centos LTSP server for our Library died near the
end of June.  My students had been playing with a new 10.04 64 setup and
 had it serving 32 bit fat clients, but really slowly.  One of the
students altered something in iptables to make it function and I wonder
if this could be the problem.  Grepping my history for iptables shows:

 49  sudo iptables --table nat --append POSTROUTING --jump MASQUERADE  --source

 50  sudo sh -c 'iptables-save > /etc/ltsp/nat'

This was done, apparently, to allow the system to function with one nic.

The system is sitting on a 100 megabit network with 26
clients.  Only 1/3 to 2/3 of the clients will boot right off.  The
others will linger with 4 four little streaming dots in the middle of
the screen for minutes until the log in screen appears or they fail with

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
INFO: task modprobe:436 blocked for more than 120 seconds.
"echo 0 >... same as 1st line

INFO: task udev-configure-:936 blocked for more than 120 seconds.
"echo 0 > ...same as 1st line
INO: taskhdparm:1020 blocked for more than 120 seconds.
"echo 0 > ...same as 1st line

INFO: task S32ltsp-client-:1027 blocked for more than 120 seconds.

It doesn't seem any better it I boot fewer clients or more... They just don't all start up reliably.

The clients run awesomely once students get logged on.

Does anyone know what the problem could be?  I'm wondering if the natting is the problem or if I have other issues.

Thanks everyone,



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