Hi, I'm new to both graph-tool and Ubuntu, which I'm installing it on (as a virtual machine on my Windows 10 computer). I've downloaded graph-tool 2.27 in my 'downloads' folder, and then followed the install instructions at https://git.skewed.de/count0/graph-tool/wikis/installation-instructions: Installation via package managers However, this produces some error messages. Do I need to locate some or all of the files I downloaded onto a specific location on my virtual machine? Here's the output I get: VirtualBox:/etc/apt$ sudo apt-get update [sudo] password: Hit:1 http://ie.archive.ubuntu.com/ubuntu bionic InRelease Get:2 http://security.ubuntu.com/ubuntu bionic-security InRelease [83.2 kB] Get:3 http://ie.archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB] Get:4 http://ie.archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB] Ign:5 http://downloads.skewed.de/apt/raring raring InRelease Err:6 http://downloads.skewed.de/apt/raring raring Release 404 Not Found [IP: 74.50.54.68 80] Get:7 http://ie.archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages [351 kB] Get:8 http://ie.archive.ubuntu.com/ubuntu bionic-updates/main i386 Packages [315 kB] Get:9 http://ie.archive.ubuntu.com/ubuntu bionic-updates/main amd64 DEP-11 Metadata [146 kB] Get:10 http://ie.archive.ubuntu.com/ubuntu bionic-updates/main DEP-11 48x48 Icons [39.1 kB] Get:11 http://ie.archive.ubuntu.com/ubuntu bionic-updates/main DEP-11 64x64 Icons [73.9 kB] Get:12 http://ie.archive.ubuntu.com/ubuntu bionic-updates/universe amd64 Packages [206 kB] Get:13 http://ie.archive.ubuntu.com/ubuntu bionic-updates/universe i386 Packages [206 kB] Get:14 http://ie.archive.ubuntu.com/ubuntu bionic-updates/universe amd64 DEP-11 Metadata [183 kB] Get:15 http://ie.archive.ubuntu.com/ubuntu bionic-updates/universe DEP-11 48x48 Icons [168 kB] Get:16 http://ie.archive.ubuntu.com/ubuntu bionic-updates/universe DEP-11 64x64 Icons [277 kB] Get:17 http://ie.archive.ubuntu.com/ubuntu bionic-updates/multiverse amd64 DEP-11 Metadata [2,468 B] Get:18 http://ie.archive.ubuntu.com/ubuntu bionic-backports/universe amd64 DEP-11 Metadata [5,100 B] Reading package lists... Done E: The repository 'http://downloads.skewed.de/apt/raring raring 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. VirtualBox:/etc/apt$ sudo apt-get install python-graph-tool Reading package lists... Done Building dependency tree Reading state information... Done E: Unable to locate package python-graph-tool Any idea what is going wrong here?