Debian 8 apt-get update showing 404 Not Found

I have had same problem after correct in sources-lists. What was solve my problem:

1. Delete all files in /etc/apt/sources.list.d/ excluding

   • nginx.list containing deb http://nginx.org/packages/debian jessie nginx
   • vesta.list containing deb http://apt.vestacp.com/stretch/ stretch vesta

2. Edit /etc/apt/sources.list to:

    deb http://httpredir.debian.org/debian stretch main contrib non-free
    deb http://httpredir.debian.org/debian stretch-updates main contrib non-free
    deb http://security.debian.org stretch/updates main contrib non-free
   

3. After that apt update && apt upgrade works well

Just keep the file which contain :

deb https://packages.sury.org/php/ jessie main

Under your /etc/apt/sources.list.d/ then update :

apt update

If you have one file , you can comment/remove other urls:

# deb http://ppa.launchpad.net/certbot/certbot/ubuntu jessie main
# deb-src http://ppa.launchpad.net/certbot/certbot/ubuntu jessie main
# deb http://ppa.launchpad.net/ondrej/php/ubuntu jessie main
# deb-src http://ppa.launchpad.net/ondrej/php/ubuntu jessie main
# deb http://ppa.launchpad.net/ondrej/php/ubuntu jessie main
# deb-src http://ppa.launchpad.net/ondrej/php/ubuntu jessie main
# deb https://packages.sury.org/php/ jessie main

deb https://packages.sury.org/php/ jessie main

So this shows you are successfully downloading repo updates from Debian Jessie[*], but not two of your third-party repos.

Based on information pointed out by other commenters, it looks like these particular repos no longer support your operating system.

[*] Debian 8 is currently "oldstable", and has been so for nearly one year. After June 2018, it will be supported by the Debian LTS project instead of the original Debian security team. If you plan to stay with Debian LTS, please make sure you're familiar with what this means. In particular "a few packages will not be supported in the LTS version of the release, primarily some web-based applications which cannot be supported for the additional timeframe. The tool check-support-status from the package debian-security-support helps to detect such unsupported packages."

(It might also be relevant to consider that backports will also stop getting updates. However backports is already not officially supported by the security team, i.e. there were not the same promises in the first place).

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One possibility is that you would want to remove the package versions installed specifically from a PPA, and then switch to a different source which supports your operating system.

You should probably take care to make sure that you have entirely switched to the new source, and don't have any packages still installed from the PPA which you are trying to replace. (This is less important in the strange case where it's really the same repo, but the location where the repo is hosted has been changed).

I found the following blog post about how to identify packages installed from a PPA which you have since removed:

Remove a PPA and roll back changes in Debian | Flynsarmy

via searching 'debian uninstall PPA', and then 'debian "ppa-purge"' (when I got results for Ubuntu telling me about ppa-purge).

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If you’re a Ubuntu user, you may be familiar with ppa-purge. It’s a handy little automated script to remove a PPA and roll back the version of any apps installed from that PPA. Debian doesn’t have this nicety by default but there’s a relatively simple way to get something close.

Firstly, remove your PPA from /etc/apt/sources.list or from the /etc/apt/sources.list.d/ directory.

Do an update:

sudo apt-get update

Find any packages that are now obsolete:

aptitude search '?obsolete'

For me this returned the following:

# aptitude search '?obsolete'
i A libmysqlclient18      - MySQL database client library                                                                           
i A mysql-client-5.5      - MySQL database client binaries                                                                          
i A mysql-server-5.5      - MySQL database server binaries and system database setup                                                
i A mysql-server-core-5.5 - MySQL database server binaries                                                                          
i A ruby-passenger        - Rails and Rack support for Apache2 and Nginx

Now just remove the listed packages with apt-get remove and reinstall as necessary. It’s not quite the automated tool that ppa-purge is, but it’s a pretty good start.