Change IP Address in Ubuntu Server 12.04 LTS
In Linux everything is a file. For almost everything including the devices that are connected to the system, you will be able to easily access the file related to it. To edit IP Address you have to open networking file using a text editor. In this example I will be using vi to change IP Address information.
Configure your Server to use DHCP on the network
Enter Networking services file with the following command.
sudo vi /etc/network/interfaces
To insert text into the text file. Press the letter "I" on your keyboard and insert the following two lines. Note that, you will already have a line with "auto lo". Don't overwrite these two lines, it's called the loopback network interface. By default you will have eth0 for network interface. If you have multiple network interfaces it will start from zero, like eth0, eth1.
iface eth0 inet dhcp
After finishing, press Esc key, type ":wq" and press Enter. "w" means "write, "q" means quit. By combining wq, it writes the changes to the file and quits the vi editor. If you want to exit vi editor without saving changes, just include the letter "q" only.
Now restart Networking Service with the following command
sudo /etc/init.d/networking restart
Manual IP Addresses Configuration
Configuring DHCP is easy isn't it? Now let us manually assign IP Address to our server. Usually servers have manually assigned IP Addresses.
Now, enter Networking Services file with the following command.
sudo vi /etc/network/interfaces
Now enter the following lines and save the file.
iface eth0 inet static
Tip: Look at the difference between manual IP configuration and DHCP. There are two differences.
It is determined whether it's static or dynamic at the end of second line.
Static has these extra lines, address, netmask, network, broadcast and gateway. Just memorize these differences.
Edit the DNS settings file
Type the following command to edit the DNS file for manual entries. If you want to switch back to DHCP, make sure the file contents are cleared, otherwise network connection would be using the manual DNS entries.
sudo vi /etc/resolvconf/resolv.conf.d/base
This is just a blank file. Now enter your DNS ip addresses like below. You can have a single or two DNS addresses. Two addresses are always recommended.
Type the following command to reboot the computer.
Now test if you can ping to www.google.com with the following command, to make sure everything is alright. Or try pinging to your router or another pc. To stop the ping command press Ctrl+C.
Now type the following command to make sure the system is using the DNS you have set previously.
sudo vi /etc/resolv.conf
resolv.conf file contains dns entries which are automatically updated by the system. This file will show the actual DNS IP addresses you are using now. You can change DNS IP addresses from here also, but it would change every time when the system is restarted. resolv.conf loads data from two places. One is the IP addresses provided by DHCP and the other is the IP addresses written in resolv.conf.d/base file.
To quit the file without writing to it, press Esc, type ":q" then Enter.
Hope this helped you :-)
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