Trouble installing curl on Ubuntu 18.10?

Question

ubuntu

I found a guide on losst.ru on Installing Ruby in Ubuntu. The first step and already an error in the console occurs:
Step 1 Install Ruby using RVM, do:

sudo apt install curl

The problem is shown in the screenshot:
accordingly, the following steps in the instructions cannot be performed due to this problem.

Answer 1

Judging by the screenshot of the comments, there are a considerable number of other people's repositories. They may be the cause of the OS update issue.
It is worth moving their .list files temporarily to another directory or simply deleting them after creating a backup copy:

sudo tar cf /etc/apt/bak-sources.tar /etc/apt/sources.list.d/ && sudo rm /etc/apt/sources.list.d/*

Make sure the copy is created:
ls /etc/apt/bak-sources.tar
Now you can

sudo apt update
sudo apt upgrade

If the picture is the same, then replace ru with us:

sudo sed -i 's/ru\.archive/us.archive/g' /etc/apt/sources.list

and re-update.
Added later
I got it. This distribution can no longer receive OS updates, as its support period has long expired (over a year ago).
https://fridge.ubuntu.com/2019/07/19/ubuntu-18-10-...

Answer 2

It says, try "sudo apt update".
Or change the repository mirrors.