Repositories (K) Ubuntu

Working with repositories in (K) Ubuntu

nano /etc/apt/source.list:

add here any repositories.

sudo aptitude update and install any software

but if you see error like "key 5A9BF3BB4E5E17B5 no found":

gpg --recv-keys 5A9BF3BB4E5E17B5
gpg --armor --export 5A9BF3BB4E5E17B5 | apt-key add -

after that sudo aptitude update and install software.

or

sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com  5A9BF3BB4E5E17B5