During the installation of docker on Ubuntu 18.04, after the line
$ sudo add-apt-repository \ "deb [arch=amd64] https://download.docker.com/linux/ubuntu \ $(lsb_release -cs) \ stable"
Sudo mode stop working with message
bash: /usr/bin/sudo: Operation not permitted. How to deal with it?
Also it is important to mention, that at the moment of executing of the last command, the
Tor mode was activated. Initially I've just missed it.
The output of the command was approximately the same as after
sudo apt-get update
The problem was solved by simple restarting of the computer.