Error when I run sudo apt-get update - have disco on bionic system

sudo apt-get update 
Hit:1 http://security.ubuntu.com/ubuntu bionic-security InRelease
Hit:2 http://archive.ubuntu.com/ubuntu bionic InRelease
Ign:3 http://archive.ubuntu.com/ubuntu disco InRelease
Hit:4 http://archive.ubuntu.com/ubuntu bionic-updates InRelease
Err:5 http://archive.ubuntu.com/ubuntu disco Release
  404  Not Found [IP: 91.189.88.142 80]
Reading package lists... Done
E: The repository 'http://archive.ubuntu.com/ubuntu disco Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: Skipping acquire of configured file 'u/binary-i386/Packages' as repository 'http://archive.ubuntu.com/ubuntu bionic-updates InRelease' doesn't have the component 'u' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'u/binary-amd64/Packages' as repository 'http://archive.ubuntu.com/ubuntu bionic-updates InRelease' doesn't have the component 'u' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'u/i18n/Translation-en' as repository 'http://archive.ubuntu.com/ubuntu bionic-updates InRelease' doesn't have the component 'u' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'u/i18n/Translation-en_US' as repository 'http://archive.ubuntu.com/ubuntu bionic-updates InRelease' doesn't have the component 'u' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'u/dep11/Components-amd64.yml' as repository 'http://archive.ubuntu.com/ubuntu bionic-updates InRelease' doesn't have the component 'u' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'u/dep11/icons-48x48.tar' as repository 'http://archive.ubuntu.com/ubuntu bionic-updates InRelease' doesn't have the component 'u' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'u/dep11/icons-64x64.tar' as repository 'http://archive.ubuntu.com/ubuntu bionic-updates InRelease' doesn't have the component 'u' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'u/cnf/Commands-amd64' as repository 'http://archive.ubuntu.com/ubuntu bionic-updates InRelease' doesn't have the component 'u' (component misspelt in sources.list?)

my /etc/apt/sources.list

deb http://archive.ubuntu.com/ubuntu bionic main universe multiverse restricted
deb http://security.ubuntu.com/ubuntu/ bionic-security main multiverse universe restricted
deb http://archive.ubuntu.com/ubuntu disco main multiverse universe restricted
deb http://archive.ubuntu.com/ubuntu bionic-updates main multiverse u

You have to rename disco (19.04, EOL) entry to correct supported bionic (18.04 LTS, supported until 2023 free).
Open terminal and execute:

sudo sed -i "s/disco/bionic/g" /etc/apt/sources.list

then fix corrupted line with main multiverse u by

sudo sed -i "s/main multiverse u$/main multiverse universe restricted/g" /etc/apt/sources.list

and then run sudo apt-get update again.

The next recommended step is to install all upgrades with newest dependencies by sudo apt-get dist-upgrade .

Good resource to read - man sources.list locally or online.