Running a recent Git for Ubuntu can sometimes be problematic. The Git version in the offical Ubuntu archives lags behind the maintainers, stable, version. To solve this install the Maintainers team version.

Add the PPA (personal Packages Archive) to your apt sources

deb http://ppa.launchpad.net/git-core/ppa/ubuntu precise main

deb-src http://ppa.launchpad.net/git-core/ppa/ubuntu precise main

or

sudo add-apt-repository ppa:git-core/ppa

if add-apt-repository is not installed, install it with apt-get install python-software-properties

sudo apt-get update && sudo apt-get install git

In a corporate environment the case of an unverified key can rise a problem. Cause is that

apt-key adv --recv-keys ;

may not work behind some firewalls. To solve this issue, follow these steps:

Open http://keyserver.ubuntu.com/ in a Browser and search for the offending key. Don’t forget to mark the string as hex by prepending 0x.

Get key from Ubuntu keyserver

Insert into a file

apt-key add <file>
apt-get update

For details see opensourceforgeeks