翻译自https://linuxhint.com/ubuntu_20-04_network_configuration/

Whether you are a Linux administrator or regular user, you must know the basics of network configuration in your Linux system. it might be helpful when troubleshooting the issues with internal and external connectivity. The basic knowledge involves knowing the interface name, the current IP configuration, and the hostname. Also, you should know how to change the default configurations to the customized settings.

In this article, we will be covering how to:

• View current IP address
• Set static IP address             设置静态IP
• Set the dynamic IP address  设置动态IP
• View current hostname         查看主机名称
• Change hostname                 修改主机名称

Note: We have run the commands and procedure mentioned in this article on the Ubuntu 20.04 system.

View Current IP Address

To view the current IP address of your machine, you can use either of the following commands:

Or

Running either of the above commands will display the IP address information. Note down the name of the interface from the output of the above command.

Set Static IP Address

In the following procedure, we will see how to set up the static IP in a Ubuntu system.

Ubuntu 20.04 uses netplan as a default network manager. The configuration file for the netplan is stored in the /etc/netplan directory. You can find this configuration file listed in the /etc/netplan directory the following command:

The above command will return the name of the configuration file with the .yaml extension, which in my case was 01-network-manager-all.yaml.

Before making any changes to this file, make sure to create a backup copy of it. Use the cp command to do so:

Note: You might have a configuration file with the name other than the 01-network-manager-all.yaml. So make sure you use the right configuration file name in the commands.

You can edit the netplan configuration using any text editor. Here we are using the Nano text editor for this purpose.

Then add the following lines by replacing the interface name, IP address, gateway, and DNS information that fit your networking needs.

Once done, save and close the file.

Now test the new configuration using the following command:

If it validates the configuration, you will receive the configuration accepted message; otherwise, it rolls back to the previous configuration.
Next, run the following command to apply the new configurations.

After this, confirm the IP address of your machine using the following command:

It should reflect the changes you have made.

Set the Dynamic IP Address

In the following procedure, we will see how to configure the interface to receive a dynamic IP address from DHCP. Edit the netplan configuration file using any text editor. Here we are using the Nano text editor for this purpose.

Then add the following lines by replacing the interface name with your system’s network interface.

Once done, save and close the file.

Now test the new configuration using the following command:

If it validates the configuration, you will receive the configuration accepted message, otherwise, it rolls back to the previous configuration.

Next, run the following command to apply the new configurations.

After this, check the IP address of your machine using the following command:

View Current Hostname

To view the current hostname, you can use either of the following commands:

or

Change Hostname

There are two different ways to change the hostname of the system. To change the hostname of the system, you must be a root user or a standard user with sudo privileges.

Using the Hostnamectl Command

To change the hostname of the system to a new name, use the following command:

Example:

This command will change the hostname of the system to “desktop”.

After that, reboot the system and you will see the new hostname assigned to your system.

Using Hostname Command

Hostname command can also be used to change the hostname of the system. Use the following command to change the hostname of the system:

This command changes the hostname of the system temporarily. To permanently change the hostname, you will need to edit the /etc/hostname and /etc/hosts file.

Use the following command to edit the /etc/hostname file:

Replace the old hostname with the new name, then save and exit the file.

Next, use the following command to edit the /etc/hosts file:

Replace the old hostname with the new name, then save and exit the file.

After that, reboot the system and you will see the new hostname assigned to your system.

Once you are done with basic network configurations, use the ping command to verify the connectivity of your system with other systems on the network and the external network.

That is all the basics you need to know about network configuration in Ubuntu 20.04 system. Note that if you have multiple network interfaces, you will have to perform IP configurations for each interface. I hope you liked the article!

How to Check Route Table？
ip route show

davidyin@u20:~$ ip route show

default via 192.168.1.1 dev ens18 proto dhcp src 192.168.1.158 metric 100
192.168.1.0/24 dev ens18 proto kernel scope link src 192.168.1.158
192.168.1.1 dev ens18 proto dhcp scope link src 192.168.1.158 metric 100
davidyin@u20:~$
Other commands I am not using.
Add Static Route

# ip route add 10.10.20.0/24 via 192.168.1.100 dev eth0
Remove Static Route
# ip route del 10.10.20.0/24

Add default gateway
# ip route add default via 192.168.1.100

Add an IP address to a specific interface
# ip addr add 192.168.1.5 dev eth1

Remove an IP address
# ip addr del 192.168.1.5/24 dev eth1

I always like to use a Router to assign a static IP to the network device. I just need to know the MAC address then I can do it at DD-WRT router.

Ubuntu 20.04 网络配置