I'm not sure what's going on or what happened. I run an Ubuntu 20.04.2 LTS machine headless. It performed an update sometime overnight and when I logged in, it prompted me that it needed a reboot. So I did, however, it didn't appear to come back up.

After attaching a monitor to it, I discovered that it was running, but the network interface was not functional. Not even appearing actually, like it was just deleted or removed. I'll try to share as much information here, but I'm just not sure what could be wrong and I honestly don't know where else to look.

After trying everything below, I still have no internet connection. What's worse, after a reboot the only way to get an IP address on my LAN to allow an SSH is by using:

$ sudo ip link set enp3s0 down

$ sudo ip link set enp3s0 up

$ sudo ip addr add 192.168.1.150/24 dev enp3s0

$ sudo lshw -class network

  *-network                 

       description: Ethernet interface

       product: RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller

       vendor: Realtek Semiconductor Co., Ltd.

       physical id: 0

       bus info: pci@0000:03:00.0

       logical name: enp3s0

       version: 0c

       serial: 2c:56:dc:97:80:9f

       size: 1Gbit/s

       capacity: 1Gbit/s

       width: 64 bits

       clock: 33MHz

       capabilities: pm msi pciexpress msix vpd bus_master cap_list ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation

       configuration: autonegotiation=on broadcast=yes driver=r8169 driverversion=5.8.0-48-generic duplex=full firmware=rtl8168g-2_0.0.1 02/06/13 ip=192.168.1.150 latency=0 link=yes multicast=yes port=MII speed=1Gbit/s

       resources: irq:18 ioport:e000(size=256) memory:fea00000-fea00fff memory:f0800000-f0803fff

$ sudo nano /etc/netplan/netcfg.yaml

network:

  version: 2

  renderer: networkd

  ethernets:

    enp3s0:

      dhcp4: no

      addresses:

        - 192.168.1.150/24

      gateway4: 192.168.1.1

      nameservers:

          addresses: [8.8.8.8, 1.1.1.1]

After a reboot, the above netplan configuration remains, however, additional spacing is being added to some of the lines - causing it to fail.

$ ip a

2: enp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000

    link/ether 2c:56:dc:97:80:9f brd ff:ff:ff:ff:ff:ff

    inet 192.168.1.150/24 scope global enp3s0

       valid_lft forever preferred_lft forever

    inet6 2001:1970:4a26:8100:2e56:dcff:fe97:809f/64 scope global dynamic mngtmpaddr 

       valid_lft 86140sec preferred_lft 14140sec

$ ip route show

default via 192.168.1.1 dev enp3s0 

172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1 linkdown 

172.18.0.0/16 dev br-5c71e5479641 proto kernel scope link src 172.18.0.1 

192.168.1.0/24 dev enp3s0 proto kernel scope link src 192.168.1.150

I am only able to get the default via 192.168.1.1 dev enp3s0 portion to appear after running sudo ip route add default via 192.168.1.1.

$ sudo netplan --debug try

DEBUG:enp3s0 not found in {}

DEBUG:Merged config:

network:

  ethernets:

    enp3s0:

      addresses:

      - 192.168.1.150/24

      dhcp4: false

      gateway4: 192.168.1.1

      nameservers:

        addresses:

        - 8.8.8.8

        - 1.1.1.1

  renderer: networkd

  version: 2



DEBUG:New interfaces: set()

** (generate:53716): DEBUG: 22:58:01.445: Processing input file /etc/netplan/netcfg.yaml..

** (generate:53716): DEBUG: 22:58:01.445: starting new processing pass

** (generate:53716): DEBUG: 22:58:01.446: We have some netdefs, pass them through a final round of validation

** (generate:53716): DEBUG: 22:58:01.446: enp3s0: setting default backend to 1

** (generate:53716): DEBUG: 22:58:01.446: Configuration is valid

** (generate:53716): DEBUG: 22:58:01.446: Generating output files..



An error occurred: the configuration could not be generated



Reverting.

DEBUG:netplan generated networkd configuration changed, restarting networkd

DEBUG:enp3s0 not found in {}

DEBUG:Merged config:

network:

  ethernets:

    enp3s0:

      addresses:

      - 192.168.1.150/24

      dhcp4: false

      gateway4: 192.168.1.1

      nameservers:

        addresses:

        - 8.8.8.8

        - 1.1.1.1

  renderer: networkd

  version: 2



DEBUG:no netplan generated NM configuration exists

DEBUG:enp3s0 not found in {}

DEBUG:Merged config:

network:

  ethernets:

    enp3s0:

      addresses:

      - 192.168.1.150/24

      dhcp4: false

      gateway4: 192.168.1.1

      nameservers:

        addresses:

        - 8.8.8.8

        - 1.1.1.1

  renderer: networkd

  version: 2



DEBUG:Link changes: {}

DEBUG:netplan triggering .link rules for lo

DEBUG:netplan triggering .link rules for enp3s0

DEBUG:netplan triggering .link rules for br-5c71e5479641

DEBUG:netplan triggering .link rules for docker0

DEBUG:netplan triggering .link rules for vethf90fcb2

DEBUG:netplan triggering .link rules for veth71540be

DEBUG:netplan triggering .link rules for veth18e90b7

DEBUG:netplan triggering .link rules for vetheb58aaa

DEBUG:netplan triggering .link rules for veth728e8e9

DEBUG:netplan triggering .link rules for veth96def70

DEBUG:netplan triggering .link rules for vetha4b92ad

DEBUG:netplan triggering .link rules for vethd43e21c

DEBUG:netplan triggering .link rules for vethb777853

DEBUG:netplan triggering .link rules for veth2b054d4

DEBUG:netplan triggering .link rules for veth8f6354f

DEBUG:netplan triggering .link rules for vethc69182e

DEBUG:netplan triggering .link rules for veth9e52006

DEBUG:netplan triggering .link rules for veth9b90b02

DEBUG:netplan triggering .link rules for veth3f22dda

DEBUG:netplan triggering .link rules for vethc39e6d3

DEBUG:netplan triggering .link rules for vetha38ae56

DEBUG:netplan triggering .link rules for vethf68a144

DEBUG:enp3s0 not found in {}

DEBUG:Merged config:

network:

  ethernets:

    enp3s0:

      addresses:

      - 192.168.1.150/24

      dhcp4: false

      gateway4: 192.168.1.1

      nameservers:

        addresses:

        - 8.8.8.8

        - 1.1.1.1

  renderer: networkd

  version: 2

This is about all the information I have. I'm just not sure what went wrong, where, how, when.

Any help is greatly appreciated. Thanks!