Your 16.04 system can be upgraded directly to 18.04. It's because both are LTS versions. This means you do not have to do a clean install (reinstallation) or reformatting your disk. I have successfully upgraded my 16.04 LTS to 18.04 by keeping the Unity 7 desktop along with the new GNOME 3 by using command lines on Terminal. If you want it, then follow instructions below.
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Read also tutorial to install Ubuntu 18.04 LTS and beta 2 review the series.
Advantages
- Keep Unity 7 desktop along with GNOME 3, not deleting it.
- Keep your installed programs, but upgrade their versions, not deleting them.
- Keep your stored files & folders, not deleting them.
- No reinstallation of the system.
- No reformatting of your hard disk drive.
- With Terminal, all processes are clearer and easier to troubleshoot if there is any trouble arises.
1. First: Upgrade to Latest 16.04 LTS
$ sudo apt-get update
$ sudo apt-get upgrade --yes
$ sudo apt-get dist-upgrade --yes
Those commands make sure your 16.04 LTS is upgraded to the latest point release of 16.04, that is 16.04.4 for now. This is important before the real upgrade to an upper LTS version.
Remember, those three commands will download up to 600MB or more of packages and takes up to 2 hours or more of time to finish all configurations. So wait patiently until all processes finished.
2. Second: Upgrade to 18.04 LTS
$ sudo do-release-upgrade
and press Y and press Enter.
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| You should not see this |
You should see a message saying that 18.04 LTS is available or many packages available to be upgraded (see picture below). If you see no upgrade available (like picture above), then change the command into:
$ sudo do-release-upgrade -d
and press Y and press Enter.
 |
| You should see this |
3. Third: Accept Removal of Packages
The terminal screen will ask your permission to remove some packages:
press Y and press Enter.
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| See the removal message |
4. Fourth: Accept Restart
Finally, if there is no error, the terminal screen will say that the system upgrade completed and ask your permission to reboot to finish up all new configurations:
press Y and press Enter.
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| Upgrade complete, now restart |
The Result
This is the desktop of the new Ubuntu 18.04 LTS upgraded from 16.04. Also, the following is the desktop of Unity 7 from 16.04, not deleted, and you will get it from the login screen > select gear icon > select Unity.
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| The original desktop of Ubuntu 18.04 |
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| The Unity 7 desktop on the same 18.04 |
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