How to recover network

[azo]

Linux version: Ubuntu 16.04 server amd64, VirtualBox VM

Occasionally network access stopped to work on the server.
Command ifconfig gives only lo interface.

ifconfig.lo.png (6.24 KiB) Viewed 243 times

First attempt was to change network adapter in VM settings.
I even changed MAC and added an extra network adapter.
No result yet

VirtualBox. network settings

VM settings.png (18.51 KiB) Viewed 243 times

It looks there was some problem with network drivers.
No Internet connection.

When I need to fix something in Windows and nothing works, I normally get Windows installer (CD .. or even USB stick).
I goggled possibility to do similar things using Linux live CD.

"The easiest way is boot from an installation media and then use chroot" (https://askubuntu.com/questions/319798/ ... -on-ubuntu)

And I found good explanation on that:
http://ubuntu.fliplinux.com/1836.html (Russian) - exactly related to the subject
https://help.ubuntu.com/community/LiveCdRecovery (English)

The idea was to re-install network manager

In case of having Internet connection, it would be done in the following way

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sudo apt-get install network-manager

Without Internet (network does not work), I needed to get Ubuntu 16.4 iso image. Old Gitlab server has the same version.

When I boot from Live CD, I found single HDD and its main partition as /dev/sda1.

fdisk output

sda1.png (58.08 KiB) Viewed 243 times

In terminal window I executed the following commands

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sudo mount /dev/sda1 /mnt
sudo mount --bind /sys /mnt/sys
sudo mount --bind /proc /mnt/proc
sudo mount --bind /dev /mnt/dev
sudo mount --bind /dev/pts /mnt/dev/pts
sudo cp /etc/resolv.conf /mnt/etc/
sudo chroot /mnt

chroot.png (30.52 KiB) Viewed 243 times

Now further installations will be applied to real HDD, and not to live (temp) system

Internet connection works on the Live (temp) system

two network interfaces.png (61.53 KiB) Viewed 243 times

First I had to install latest updates to current Ubuntu 16.4

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sudo apt-get update

sudo apt-get upgrade (desired... but probably not really necessary)
Upgrade may take a while since more than 1 Gbytes should be downloaded and installed.

Then network manager can be (re)installed

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sudo apt-get install network-manager

This command did not work. There was error message with recommendation to execute 'sudo dpkg --configure -a'
After that command (executed for a while), I tried to install network manager again

dpkg.png (11.5 KiB) Viewed 243 times

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sudo dpkg --configure -a

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sudo apt-get install network-manager

I restarted the server without Live CD. And it appeared network is working!!!

Normally I install Midnight Commander (mc). I like GUI. And that allows me to browse files easily.

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sudo apt-get install mc

That is all.