Limit download speed in apt-get

# sudo vim /etc/apt/apt.conf.d/76download
Add lines below:
================

Acquire
{
Queue-mode "access";
http
{
Dl-Limit "25";
};
};
================

These codes will limit speed to 25KB/s, when you are in command mode or using Synaptic Package Managemer (GUI).

Ref: http://www.associatedcontent.com/article/2717695/ubuntu_limiting_download_speed_in_synaptic.html