"Turn" the role and difference of Ubuntu sudo update and upgrade

This article turns from http://www.baiyuxiong.com/?p=529

The Beginner Linux comrades, at the beginning of the most urgent to know, about one is the Chinese input method, the other is how to install software. This article mainly describes the Linux installation software features.
Under Windows to install the software, we only need to have EXE file, and then double-click, the next step directly OK. But under Linux, that's not the case. Every Linux distribution, like Ubuntu, maintains a repository of its own, and almost all of the software we use is here. The software is absolutely safe and absolutely normal to install.
So how are we going to install it? In Ubuntu, we maintain a source list, the source list is some URL information, each URL is a source, this address points to the data that identifies the source server on which software can be installed to use.
Edit Source Command:

1	sudo gedit/etc/apt/sources.list

Add or comment (add #) to the file and save it after you drop some sources. At this point, the software that our source list points to will increase or decrease the portion.
The next thing to do is:

1	sudo apt-get update

This command accesses each URL in the source list and reads the software listing, which is then saved on the local computer. The list of software that we see in the newly made Package manager is updated with the update command.

After the update, you may need to upgrade.

1	sudo apt-get upgrade

This command will compare the locally installed software with the software listed in the software list you just downloaded, and if you find that the installed software version is too low, you will be prompted to update it. If your software is the latest version, you will be prompted:

1	0 packages were upgraded, 0 new packages were installed, 0 packages were uninstalled, 0 packages were not upgraded.

In summary, update is the list of updates, and upgrade is the update software.

Plus

Upgreade can not mess with Ah, if the source has a system update, directly to you to upgrade the system.

"Turn" the role and difference of Ubuntu sudo update and upgrade