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 follows:
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.
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 able to “see” each other and communicate.
A malfunctioning or completely broken NTP service could affect Kerberos authentication and X server functionality.
If any application needed data stored in an NFS mounted
directory, it would not be able to start up 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 his
subdirectories could not be found due to an outage of the NFS
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.
If your SUSE Linux 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.
If your SUSE Linux 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.
Authentication would not work and login to any machine would fail.
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. We assume both server and client to be members of the same subnet without the need for additional routing.
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
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 ping
your_hostname from another
machine. If you succeed to reach your machine from another machine, it
is the server that is not running at all or not configured correctly.
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 Step 4.b. If ping still
fails, either your network card is not configured correctly or
your network hardware is faulty. Refer to Step 4.c for information about this.
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 this the
host command fails, check all network
configuration files relevant to name and address resolution on your
This file is used to keep track of the name server and domain you are currently using. It can be modified manually or be 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 Hostname module.
If your network connection is handled via DHCP, enable DHCP to change hostname and name service information by selectingand 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 ...
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 Chapter 20, 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
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 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
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.