I found the following message when I was trying to install CVS on Ubuntu 10.04 with synaptic,
Please insert the disk labeled: Ubuntu 10.04 LTS _Lucid Lynx_ – Release i386 (20100427.1) in drive /cdrom/
I am not sure why is this message appears. But my Ubuntu 10.04 was upgraded from Ubuntu 9.10 with the alternative CD. Fortunately, I got the CD image. Thus, to solve this problem, I mount the alternative CD to the “/cdrom/” drive. Then, there is no problem for the installation.
sudo mount -o loop ubuntu-10.04-alternative-i386.iso /cdrom/
Only the alternative CD works, the desktop CD cannot work.