Unable to open /etc/network/interfaces - install Ubuntu 20.04 container

Ubuntu 20.04 in a virtual container Proxmox 6.3-2
Virtualmin 6.2.0

Just install a new container Ubuntu 20.04 on my Proxmox 6 server.

I only make Ubuntu upgrades.
I try to install Virtualmin 6.2.0 with the script.

Failed …

[9/23] Configuring Net

Unable to open /etc/network/interfaces :flushed:

Folder /etc/network exist.
But not the “interfaces” file…

Why it doesn’t work in a virtual container ? :confused:


Is it link to NETPLAN ? :flushed:

In my Ubuntu 20.04 container, /etc/netplan/ folder is empty.

In my Ubuntu 20.10 desktop, 1 file exist : /etc/netplan/01-network-manager-all.yaml

Does I need to create VM, and not container, in Proxmox ?

Thanks. Didier


Yes, we would recommend using minimal, non modified instance of OS.

It’s an Ubuntu 20.04 server template for Proxmox.
i always use this kind of template. Never has this kind of problem… :flushed:

I think first Proxmox template I use was Ubuntu 14.04… after I use 16.04, 18.04 without problem.

I create an Ubuntu Server VM in Proxmox (not a container), from the Ubuntu server ISO downloader from Ubuntu site.
Virtualmin script is running well and no error ! :smiley:

The /etc/network/interfaces exist : “interfaces” is empty.

I will try again with a container, just to know… :thinking:

… so does your system uses Netplan or ifupdown? If you are not sure, contact your service provider with this question.

it’s my install, base on Ubuntu ISO.
Network on this VM is NETPLAN setting :thinking:
I don’t configure Netplan… It seems to be default network setting for Ubuntu Server 20.04 LTS.

You can configure network on Webmin > Networking > Network Configuration page.

I retry on the container Ubuntu 20.04.
Failed because :thinking:


Unable to open /etc/network/interfaces

Cleaning up

[WARNING] The following errors occurred during installation:

◉ Postinstall configuration returned an error.

I try another thing in the Container (template Proxmox for Ubuntu server 20.04):

I create an “interfaces” file empty :thinking:
and the installation succeed ! :flushed: :smiley:

“interfaces” file is always empty…
So ?
I simply need to create an empty file to solve this problem ? :thinking:

doesn’t work with the container Ubuntu 20.04 version :thinking:

No interface listed… :flushed:

/etc/network/interfaces is empty

/etc/netplan folder is EMPTY too !

but “ip addr show” give correct IP and MAC address…

2: eth0@if123: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 02:00:00:72:03:93 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::ff:fe72:393/64 scope link 
       valid_lft forever preferred_lft forever

sorry, active interfaces give this :

Seem normal ?

You would need to click “Add a new interface” button and set it up.

now it works
but before it was NOT possible to “add a new interface” in the VM Ubuntu 20.04
simply because, without ANY interfaces, I cannot access to the Virtualmin web site…

So, I must first define the interface in NETPLAN in CLI with VI, apply the new settings, and now, YES I can access to Virtualmin “myserver.be:10000”.

Just another problem with the CONTAINER Ubuntu 20.04 :thinking:

Let’s Encrypt was not working (doesn’t succeed).

I solve it with “certbot register
because Let’s Encrypt was trying to use an invalid email address.

No problem with LE and Certbot in the VM test.
Probably the install script was made the Let’s Encrypt setting another way…


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