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bengisu@bengisu-VirtualBox:~/Desktop$ sudo apt-get update
[sudo] password for bengisu: 
Reading package lists... Done
bengisu@bengisu-VirtualBox:~/Desktop$ sudo apt install gcc
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package gcc is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'gcc' has no installation candidate
bengisu@bengisu-VirtualBox:~/Desktop$ sudo apt install build-essential
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package build-essential
bengisu@bengisu-VirtualBox:~/Desktop$ sudo apt install git
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package git is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'git' has no installation candidate
bengisu@bengisu-VirtualBox:~/Desktop$