/etc/network/interfaces missing in Ubuntu [SOLVED]

If you are using Ubuntu, you must have encountered the "/etc/network/interfaces missing" error. Because Ubuntu 18.04 and above uses netplan to configure your network. The /etc/network/interfaces file is no longer available in newer versions. Netplan is used instead, the configuration file is in the /etc/netplan/ directory.

For example, let's look under /etc/network on Ubuntu 22.04:

foc@ubuntu22:~$ ls /etc/network/
if-pre-up.d  if-up.d

foc@ubuntu22:~$ cat /etc/network/interfaces
cat: /etc/network/interfaces: No such file or directory

As you can see, there are no interfaces files. Let's have a look under netplan:

foc@ubuntu22:~$ ls /etc/netplan
00-installer-config.yaml

foc@ubuntu22:~$ cat /etc/netplan/00-installer-config.yaml 
# This is the network config written by 'subiquity'
network:
  ethernets:
    enp1s0:
      dhcp4: true
  version: 2

Network configuration is in yaml file. So what should we do if we want to go back to the past? Can we use the /etc/network/interfaces file? Let's see what we can do.

Network definition steps with /etc/network/interfaces

The following steps will now take you back to the past, Ubuntu only allows you to define networks in the old way.

Package Installation

In Ubuntu, two packages must be installed to configure the network settings in the interfaces file. Update the package list first:

foc@ubuntu22:~$ sudo apt update -y

Then install the packages:

foc@ubuntu22:~$ sudo apt install ifupdown net-tools

So what do these packages do?

ifupDown Package: It is used with the ifup and ifdown commands to configure (or deconfigure respectively) network interfaces based on the interface definitions in the /etc/network/interfaces file.
net-tools Package: It needs this package to form the base set of the NET-3 network distribution for Linux operating systems.

Configuring Grub

Network configuration should be translated to eth0 as in /etc/network/interfaces configurations.

In the /etc/default/grub file, the following lines are changed:

foc@ubuntu22:~$ sudo sed -i -e 's/GRUB_CMDLINE_LINUX=\"\"/GRUB_CMDLINE_LINUX=\"net.ifnames=0 biosdevname=0\"/g' /etc/default/grub

Before:

GRUB_CMDLINE_LINUX=""

After:

GRUB_CMDLINE_LINUX="net.ifnames=0 biosdevname=0"

Note: You can edit the /etc/default/grub file manually as above by opening it with a text editor (nano, vim etc).

Then update grub:

foc@ubuntu22:~$ sudo update-grub
Sourcing file `/etc/default/grub'
Sourcing file `/etc/default/grub.d/init-select.cfg'
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-5.15.0-53-generic
Found initrd image: /boot/initrd.img-5.15.0-53-generic
Found linux image: /boot/vmlinuz-5.15.0-46-generic
Found initrd image: /boot/initrd.img-5.15.0-46-generic
Found memtest86+ image: /memtest86+.elf
Found memtest86+ image: /memtest86+.bin
Warning: os-prober will not be executed to detect other bootable partitions.
Systems on them will not be added to the GRUB boot configuration.
Check GRUB_DISABLE_OS_PROBER documentation entry.
done

Finally, reboot the operating system:

foc@ubuntu22:~$ sudo reboot

Output of "ip a" command when network is managed with netplan:

foc@ubuntu22:~$ ip ad
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 52:54:00:c4:72:46 brd ff:ff:ff:ff:ff:ff
    inet 192.168.122.34/24 metric 100 brd 192.168.122.255 scope global dynamic enp1s0
       valid_lft 2416sec preferred_lft 2416sec
    inet6 fe80::5054:ff:fec4:7246/64 scope link 
       valid_lft forever preferred_lft forever

Output of "ip a" command when managed with interfaces file:

foc@ubuntu22:~$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 52:54:00:c4:72:46 brd ff:ff:ff:ff:ff:ff
    altname enp1s0
    inet 192.168.122.34/24 metric 100 brd 192.168.122.255 scope global dynamic eth0
       valid_lft 3517sec preferred_lft 3517sec
    inet6 fe80::5054:ff:fec4:7246/64 scope link 
       valid_lft forever preferred_lft forever

You can see that the "enp1s0" interfaces name has changed to "eth0". Now let's view the /etc/network/interfaces file:

foc@ubuntu22:~$ cat /etc/network/interfaces
# interfaces(5) file used by ifup(8) and ifdown(8)
# Include files from /etc/network/interfaces.d:
source /etc/network/interfaces.d/*

Now the interfaces file is available in the system.

Create New Network Interface

Of course, the interfaces file should be defined when switching to the old system. Define the following lines in the interfaces file to get ip from DHCP:

foc@ubuntu22:~$ sudo vi /etc/network/interfaces

auto eth0
allow-hotplug eth0
iface eth0 inet dhcp

First, the defined interface is down:

NOTE:

If a 2nd interface is not defined on the server, you may lose access to the server after this command. Either define a 2nd interfaces or have direct access to the server.

foc@ubuntu22:~$ sudo ifdown --force eth0
/etc/network/if-down.d/resolved: 12: mystatedir: not found
Internet Systems Consortium DHCP Client 4.4.1
Copyright 2004-2018 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/eth0/52:54:00:c4:72:46
Sending on   LPF/eth0/52:54:00:c4:72:46
Sending on   Socket/fallback
Created duid "\000\001\000\001+\033\306(RT\000\304rF".

Then turn the interface up:

foc@ubuntu22:~$ sudo ifup eth0

As you can see in the picture above, the new interface has received an IP address.

Summary

In this article, we explained the steps to define the network with the interfaces file removed in Ubuntu 18.04 and later versions. Although the steps in the article provide you with this opportunity, the methods brought by the operating system will be more stable.

In a possible update and package conflict, the first settings to be changed will be those that the operating system does not support. Therefore, it will be useful to get used to netplan.

References

askubuntu.com - Looking for /etc/network/interfaces is missing?