E: Unable to locate package code example

Example 1: E: Unable to locate package npm

curl -sL https://deb.nodesource.com/setup_10.x | sudo -E bash -
sudo apt-get install -y nodejs

Example 2: E Unable to locate package sl

sudo apt update

Example 3: ubuntu can't locate packages

sudo add-apt-repository universe multiverse

Example 4: unable to locate package node

sudo apt-get install -y build-essential

Example 5: unable to locate package node

curl -sL https://deb.nodesource.com/setup_10.x | sudo -E bash -
sudo apt-get install -y nodejs

Example 6: unable to locate package node

sudo apt install curl
curl -sL https://deb.nodesource.com/setup_6.x | sudo bash -
sudo apt-get install -y nodejs
sudo apt-get install -y npm