How to assign a static IP to a Linux machine on a local network

[isscbta]

First, check the IP address assigned to the Linux machine by DHCP:

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# ifconfig 
enp2s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 111.111.111.111  netmask 255.255.255.0  broadcast 111.111.111.255
        inet6 fe80::219:99ff:fef5:c33e  prefixlen 64  scopeid 0x20<link>
        ether 00:19:99:f5:c3:3e  txqueuelen 1000  (Ethernet)
        RX packets 21179  bytes 3719145 (3.5 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 26980  bytes 8981209 (8.5 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

From this, we find out that it is: 111.111.111.111

Now, let's look at the current version of the /etc/network/interfaces file.

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# cat /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
allow-hotplug enp2s0
iface enp2s0 inet dhcp

Let's modify it to be:

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# cat /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
allow-hotplug enp2s0
# iface enp2s0 inet dhcp # *** COMMENT THIS LINE ***

# *** ADD THIS BLOCK FOR STATIC IP ***
auto enp2s0 # NETWORK NAME (enp2s0) IS IMPORTANT, WE TOOK IT FROM PREVIOUS BLOCK
iface enp2s0 inet static # NETWORK NAME AGAIN
 address 111.111.111.111 # OUR IP THAT WE SAW A FEW MINUTES AGO
 netmask 255.255.255.0
 gateway 111.111.111.1 # THE SAME AS IP JUST ENDED WITH .1
 dns-nameservers 8.8.8.8

At the end:

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reboot