Why does my system boot so slowly?

I installed Ubuntu 10.10 a few days ago. It is really awesome but the problem is that it takes unusually long time (about 20 minutes) for the login screen to appear after the Ubuntu startup screen. This only happens if I shutdown the computer. There is no problem when I restart the computer.

The simplest way to solve this problem is with bootchart. It will let you see which process in the boot up sequence is slowing things down.

sudo apt-get install bootchart pybootchartgui

Once it is installed just start the gui at the command line with

pybootchartgui

You have to have at least rebooted once for this to work.

My guess would be that you disks were being check with fsck which happens periodically.