Configuring Static IP Address from the Command Line in Linux: A Comprehensive Guide

Before we dive into the comprehensive steps for configuring a static IP address from the Linux command line, let’s get a quick understanding of the most important commands:

TL;DR:
Firstly, use the ip link command to find out the interfaces. The interface showing up typically is the one you want to use.

ip link

Then, add your static IP address (for example, 198.32.160.100) using the ip addr command:

sudo ip addr add 198.32.160.100/24 dev eth0

Next, set the default gateway (for example, 198.32.160.1) using the ip route command:

sudo ip route add default via 198.32.160.1 dev eth0

Please note that the netmask is given in CIDR notation (it is the /24 right after the IP of the device in the ip addr command).

With this brief guide in hand, let’s delve into the finer details.

Why Set a Static IP?

Before proceeding, let’s understand why setting a static IP is necessary. Computers use IP addresses to communicate over a network. By default, your system will likely receive a dynamic IP address from the DHCP server. However, for server environments, it’s often preferable to have a static IP that doesn’t change, facilitating seamless network access and management. Dedicated servers will call these static IP addresses or just an IP address.

Configuring Static IP Address

Let’s first check your existing network interfaces using the ip addr command:

ip addr show

In the output, find the network interface you want to configure. It will typically be something like eth0 or ens160.

Next, let’s configure a static IP. Suppose we want to assign the IP address 192.168.1.100 to the interface eth0. We can do this by using the ip addr command:

sudo ip addr add 192.168.1.100/24 dev eth0

Here, 192.168.1.100 is the IP address, /24 is the subnet mask equivalent to 255.255.255.0, and eth0 is the interface name.

Tip: To remove the existing IP address, you can use the ip addr del command in a similar way.

Trick: If you want to check whether the IP has been assigned successfully, you can run the ip addr show eth0 command.

Setting the Default Gateway

After assigning the IP, you should set up the default gateway using the ip route command:

sudo ip route add default via 192.168.1.1 dev eth0

Here, 192.168.1.1 is the IP address of the gateway, and eth0 is the interface name.

Tip: To delete an existing default gateway, use the ip route del default command.

Resolving DNS

Edit the /etc/resolv.conf file to set the DNS servers:

sudo nano /etc/resolv.conf

Then, add the following lines to the file, replacing 8.8.8.8 and 8.8.4.4 with your DNS servers:

nameserver 8.8.8.8
nameserver 8.8.4.4

Save and close the file.

Trick: Always keep a backup of your original resolv.conf file before editing.

Making the Changes Permanent

These changes will be lost upon reboot. To make them permanent, you need to edit the interface configuration file. This process varies across different Linux distributions.

On Ubuntu and other Debian-based distributions, this file is usually located in /etc/network/interfaces. On RHEL, CentOS, and Fedora, it’s in /etc/sysconfig/network-scripts/, and the file name would be something like ifcfg-eth0.

Tip: Always keep a backup of your original configuration file before making changes.

Conclusion

Configuring a static IP from the command line in Linux might seem daunting initially, but with a clear understanding of the process and some helpful tips and tricks, it can become a smooth operation. Remember, a comprehensive understanding of your network setup is crucial before making any changes.

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