please tell me the command to uninstall the Nexus Repository Manager from ubuntu-18.04?
I think officially there is no document for this.
i will suggest just do following steps
sudo systemctl stop nexus
sudo rm /etc/systemd/system/nexus.service.
userdel -r nexus
after that just remove the folder where it is install(/opt/nexus)
if you need to be back then just back the folder where the db of repo resident this you can get from /bin/nexus.vmopitions.
Let us know if any query.