The Stupid Minds

Setting your hostname, IP address, netmask, gateway, DNS server via files

It is sometimes helpful to know what is going on behind the scenes or if you want to modify the network configuration via changing files.

For example, assume you want to modify the network configuration by modifying files with the following:

hostname: server
domainname: demo.eu
Static IP address: 10.0.1.23
Netmask: 255.255.255.0
Gateway: 10.0.1.254
Primary DNS server: 10.0.1.1
Secondary DNS server: 10.0.1.253

Networking is set up in these files:

/etc/sysconfig/network
/etc/sysconfig/network-scripts/ifcfg-eth0
/etc/resolv.conf

First, add your host to the /etc/hosts file:

# The next line "127.0.0.1" is needed. Do not remove it.
127.0.0.1       localhost.localdomain localhost
10.0.1.23       server

Your /etc/sysconfig/network file would be:

NETWORKING=yes
HOSTNAME=server
GATEWAY=10.0.1.23

Your /etc/sysconfig/network-scripts/ifcfg-eth0:

DEVICE=eth0
BOOTPROTO=static
BROADCAST=10.0.1.255
IPADDR=10.0.1.23
NETMASK=255.255.255.0
NETWORK=10.0.1.0
ONBOOT=yes

DNS servers are set in: /etc/resolv.conf. An example:

domain demo.eu
search demo.eu
nameserver 10.0.1.1
nameserver 10.0.1.253

Using ifconfig and route

You normally would not need to use ifconfig or route unless you want to change your IP address, disable the Ethernet interface, etc. change your gateway, etc. This is sometimes helpful, so the information is here. To set an ip address:

ifconfig eth0 10.0.1.23 netmask 255.255.255.0 up

To set a default route or gateway (“gw” = “gateway”):

route add default gw 10.0.1.254 eth0

Troubleshooting

If your system is saying there is no Ethernet card found, make sure the card is in the kernel.

Type:

modprobe eth0
dmesg | less
    Look for any info about eth0 to help track down the problem.
    
cat /etc/modules.conf
    Look for a line line this:
    alias eth0 driver-name-like-wdi or 3c503

Source: http://www.linuxmigration.com/quickref/install/network.html

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