Ubuntu 20 sudo reboot lost network and DNS issues

 

sudo lshw -numeric -C network

 

logical name: enp2s0

logical name is network interface name

 

 https://serverfault.com/questions/21475/starting-network-connection-from-ubuntu-recovery

Then do

# Restart dhcp client

sudo dhclient enp2s0

# Restart name resolution service

sudo systemctl start systemd-resolved

https://www.cyberciti.biz/faq/howto-linux-renew-dhcp-client-ip-address/#:~:text=The%20dhclient%20command%2C%20provides%20a,by%20statically%20assigning%20an%20address.

This error is mainly caused by dhcp service issues, check /etc/resolv.conf sym link***

The dhclient command, provides a means for configuring one or more network interfaces using the Dynamic Host Configuration Protocol, BOOTP protocol, or if these protocols fail, by statically assigning an address.

This is because

In newer versions of Ubuntu name resolution does not work via /etc/resolv.conf anymore.

to prevent doing this all time do :

https://askubuntu.com/questions/193074/have-to-run-sudo-dhclient-eth0-automatically-every-boot

gksu gedit /etc/rc.local

Add: sudo dhclient eth0 like so.

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
sudo dhclient eth0
exit 0

https://unix.stackexchange.com/questions/49626/purpose-and-typical-usage-of-etc-rc-local

The script /etc/rc.local is for use by the system administrator. It is traditionally executed after all the normal system services are started, at the end of the process of switching to a multiuser runlevel. You might use it to start a custom service, for example a server that's installed in /usr/local. Most installations don't need /etc/rc.local, it's provided for the minority of cases where it's needed.

If DNS name can not be resolved after above steps such as docker: 

https://stackoverflow.com/questions/47580528/error-response-from-daemon-get-https-registry-1-docker-io-v2-dial-tcp-look

sudo vim /etc/resolv.conf

#Google name server or ur known name server)

#add nameserver 8.8.8.8 

nameserver 8.8.4.4

sudo systemctl daemon-reload

sudo systemctl restart docker