Network Configuration on CentOS

Introduction

Network Configuration

To examine the connections, execute one of the commands:

• sudo ls /sys/class/net/
• ip a s
• ifconfig
• nmcli conn show

For example:

nmcli conn show

NAME UUID TYPE DEVICE enp0s3 64486a76-a4b0-4693-9110-205da942c9c5 ethernet enp0s3 enp0s8 fc26857f-4cb0-3756-a7fa-95ec246b3981 ethernet enp0s8

If some interface, for example enp0s3, is down, its DEVICE column will contain --

Usually an inactive interface is highlighted in gray and an active one in green.

NAME UUID TYPE DEVICE enp0s3 64486a76-a4b0-4693-9110-205da942c9c5 ethernet -- enp0s8 fc26857f-4cb0-3756-a7fa-95ec246b3981 ethernet enp0s8

You can bring the interface up with the command

nmcli conn up enp0s3

To avoid bringing the network interface up manually every time, you can set ONBOOT yes in the settings

Alternatively, you can open /etc/sysconfig/network-scripts/ifcfg-enp0s3 and edit it with vi or, as root, use sed

sudo sed -i s/ONBOOT=no/ONBOOT=yes/ /etc/sysconfig/network-scripts/ifcfg-enp0s3

If the command above is not entirely clear to you, read the article «Sed basics»

To check whether ONBOOT was changed to yes, use the command

grep ONBOOT !$

Installing a static IP

nmcli conn show

NAME UUID TYPE DEVICE enp0s3 64486a76-a4b0-4693-9110-205da942c9c5 ethernet enp0s3 enp0s8 fc26857f-4cb0-3756-a7fa-95ec246b3981 ethernet enp0s8

Let's set up a static IP for enp0s8

Network settings are stored in the directory

/etc/sysconfig/network-scripts/

You need to edit the file ifcfg-enp0s8

Main parameters:
TYPE - connection type, wired (Ethernet), wireless (Wired) and so on;
BOOTPROTO - the method of obtaining an IP address, static, dhcp or none;
NAME - connection name;
DEVICE - network interface name;
ONBOOT - whether it should be started at system boot;
IPADDR - the IP address that will be used for this computer;
GATEWAY - gateway for internet access;
NETMASK - network mask;
DNS1 - server for DNS domain name resolution.

sudo vi /etc/sysconfig/network-scripts/ifcfg-enp0s8

TYPE=Ethernet PROXY_METHOD=none BROWSER_ONLY=no BOOTPROTO=dhcp DEFROUTE=yes IPV4_FAILURE_FATAL=no IPV6INIT=yes IPV6_AUTOCONF=yes IPV6_DEFROUTE=yes IPV6_FAILURE_FATAL=no IPV6_ADDR_GEN_MODE=stable-privacy NAME=enp0s8 UUID=939a0551-f5b5-46d8-87fe-24e5e7b1a0c1 DEVICE=enp0s8 ONBOOT=yes

Errors and warnings

sudo systemctl restart networking

Job for network.service failed because the control process exited with error code. See "systemctl status network.service" and "journalctl -xe" for details.

systemctl status network.service

Release the IP

If the IP was obtained via DHCP, you can release it by running

sudo dhcp -r enp0s8

Instead of enp0s8, enter the name of the adapter you need

Installation ifconfig

yum provides ifconfig

or

yum whatprovides ifconfig

ifconfig is part of net-tools, for example

Let's install net-tools

sudo yum install net-tools

Change the IP

You can change the IP quickly with ifconfig

First you need to install the package containing ifconfig - following the instructions

You change the IP with the command

sudo ifconfig enp0s8 192.168.56.111

Instead of enp0s8, enter the interface you need

Instead of 192.168.56.111, enter the IP you want to set

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