13.5 Network Problems
Many problems of your system may be network-related, even though they do
not seem to be at first. For example, the reason for a system not
allowing users to log in might be a network problem of some kind. This
section introduces a simple check list you can apply to identify the
cause of any network problem encountered.
When checking the network connection of your machine, proceed as
If using an ethernet connection, check the hardware first. Make sure
that your network cable is properly plugged into your computer. The
control lights next to your ethernet connector, if available, should
both be active.
If the connection fails, check whether your network cable works with
another machine. If it does, your network card causes the failure. If
hubs or switches are included in your network setup, suspect them to be
the culprits as well.
If using a wireless connection, check whether the wireless link can be
established by other machines. If this is not the case, contact the
wireless network's administrator.
Once you have checked your basic network connectivity, try to find out
which service is not responding. Gather the address information of all
network servers needed in your setup. Either look them up in the
appropriate YaST module or ask your system administrator. The
following list gives some of the typical network servers involved in a
setup together with the symptoms of an outage.
- DNS (Name Service)
A broken or malfunctioning name service affects the network's
functioning in many ways. If the local machine relies on any network
servers for authentication and these servers cannot be found due to
name resolution issues, users would not even be able to log in.
Machines in the network managed by a broken name server would not be
see each other and communicate.
- NTP (Time Service)
A malfunctioning or completely broken NTP service could affect
Kerberos authentication and X server functionality.
- NFS (File Service)
If any application needed data stored in an NFS mounted directory,
it would not be able to start or function properly if this service
was down or misconfigured. In a worst case scenario, a user's
personal desktop configuration would not come up if his home
directory containing the .gconf or
.kde subdirectories could not be found due to
an outage of the NFS server.
- Samba (File Service)
If any application needed data stored in a directory on a Samba
server, it would not be able to start or function properly if this
service was down.
- NIS (User Management)
If your openSUSE system relied on a NIS server to provide the
user data, users would not be able to log in to this machine if the
NIS service was down.
- LDAP (User Management)
If your openSUSE system relied on an LDAP server to provide the
user data, users would not be able to log in to this machine if the
LDAP service was down.
- Kerberos (Authentication)
Authentication would not work and login to any machine would fail.
- CUPS (Network Printing)
Users would not be able to print.
Check whether the network servers are running and whether your network
setup allows you to establish a connection:
The debugging procedure described below only applies to a simple
network server/client setup that does not involve any internal
routing. It assumes both server and client are members of the same
subnet without the need for additional routing.
Use ping hostname
(replace hostname with the hostname of the
server) to check whether each one of them is up and responding to the
network. If this command is successful, it tells you that the host
you were looking for is up and running and that the name service for
your network is configured correctly.
If ping fails with destination host unreachable,
either your system or the desired server is not properly configured
or down. Check whether your system is reachable by running
from another machine. If you can reach your machine from another
machine, it is the server that is not running at all or not
If ping fails with unknown host, the name service
is not configured correctly or the hostname used was incorrect. Use
ping -n ipaddress to
try to connect to this host without name service. If this is
successful, check the spelling of the hostname and for a
misconfigured name service in your network. For further checks on
this matter, refer to
If ping still fails, either your network card is not configured
correctly or your network hardware is faulty.
Use host hostname to
check whether the hostname of the server you are trying to connect to
is properly translated into an IP address and vice versa. If this
command returns the IP address of this host, the name service is up
and running. If the host command fails, check all
network configuration files relating to name and address resolution
on your host:
This file is used to keep track of the name server and domain you
are currently using. It can be modified manually or automatically
adjusted by YaST or DHCP. Automatic adjustment is preferable.
However, make sure that this file has the following structure and
all network addresses and domain names are correct:
This file can contain more than one name server address, but at
least one of them must be correct to provide name resolution to
your host. If needed, adjust this file using the YaST DNS and
If your network connection is handled via DHCP, enable DHCP to
change hostname and name service information by selecting
and in the YaST DNS
and Hostname module.
This file tells Linux where to look for name service information.
It should look like this:
hosts: files dns
networks: files dns
The dns entry is vital. It tells Linux to use an
external name server. Normally, these entries are automatically
made by YaST, but it never hurts to check.
If all the relevant entries on the host are correct, let your
system administrator check the DNS server configuration for the
correct zone information. For
detailed information about DNS, refer to
The Domain Name System, (↑ Reference ). If you have made
sure that the DNS configuration of your host and the DNS server
are correct, proceed with checking the configuration of your
network and network device.
If your system cannot establish a connection to a network server and
you have excluded name service problems from the list of possible
culprits, check the configuration of your network card.
Use the command ifconfig
network_device (executed as
root) to check whether this
device was properly configured. Make sure that both inet
address and Mask are configured correctly.
An error in the IP address or a missing bit in your network mask
would render your network configuration unusable. If necessary,
perform this check on the server as well.
If the name service and network hardware are properly configured and
running, but some external network connections still get long
time-outs or fail entirely, use traceroute
(executed as root) to track
the network route these requests are taking. This command lists any
gateway (hop) a request from your machine passes on its way to its
destination. It lists the response time of each hop and whether this
hop is reachable at all. Use a combination of traceroute and ping to
track down the culprit and let the administrators know.
Once you have identified the cause of your network trouble, you can
resolve it yourself (if the problem is located on your machine) or let
the system administrators of your network know about your findings so
they can reconfigure the services or repair the necessary systems.
13.5.1 NetworkManager Problems
If you have a problem with network connectivity, narrow it down as
described in . If NetworkManager
seems to be the culprit, proceed as follows to get logs providing hints
on why NetworkManager fails:
Open a shell and log in as
Restart the NetworkManager:
rcnetwork restart -o nm
Open a web page, for example, http://www.opensuse.org
as normal user to see, if you can connect.
Collect any information about the state of NetworkManager in
For more information about NetworkManager, refer to
Section 10.0, Using NetworkManager.