I'm back.
johnsfine, thanks a lot for all this detailed information. Very instructive.

So I'm still in the prepare partitions window.
I made some changes so that it now looks that way :
device type mount point format? size used
/dev/sda
/dev/sda1 ntfs (nothing) (unselected) 50 GB 25 GB
/dev/sda2 ntfs (nothing) (unselected) 100 GB 3 GB
/dev/sda3 ext4 / (selected) 20 GB unknown
/dev/sda5 swap (nothing) (unselected) 4GB unknown

Can I press forward ?

Hello,

I'm almost sure you made a typing error but that's not important. You have all the partitions with sda1 which is impossible

Just click on the partition that says ext4 and then on the forward button.

Kind regards,

Eric

oh yes wrong copy/paste. Edited now.
I pressed forward. Back to the who are you window. Forward again ?

Hello and good morning,

If you filled in your details, yes, press Forward.

Kind regards,

Eric

Hello,
good morning

It was already filled in from the previous attempt.
I then got the migrate documents window, I pressed forward too.
Now the recapitulation window.

language, keyboard layout,name,login name, location, migration assistant are ok.
then :

if you continue, the changes listed below will be written to the disks.
otherwise, you will be able to make further changes manually

warning : this will destroy all data on any partitions you have removed as well as on the partitions that are going to be formatted.

the partition tables of the following devices are changed :
scsi1 (0,0,0) (sda)

the following partitions are going to be formatted :
partition #3 of scsi1 (0,0,0) sda as ext4
partition #5 of scsi1 (0,0,0) sda as swap


Can I press "install" now ?

Yes, press Install and keep your fingers crossed!

Kind regards,

Eric

Done !! thanks a lot Eric .
I'm on the desktop.
What now ?

So it installed correctly this time? Great news, I'm pleased to hear that.

Now reboot the normal way, clicking your name top right of the screen and restart. See if you can boot normally and if Ubuntu starts up correctly without any errors.

Kind regards,

Eric

Yes it's starting normally.
I didn't notice any errors.
There are quite a lot of things that need to be installed now, I'm waiting for your instructions (you said yesterday that there were procedures to do once the installation is complete so that the next reinstallation would be easier).
There is no admin user at the moment, I'm not sure I have the admin rights but I think it's safer not to.
Maybe I can remake a packages.txt so that we can compare ?

Hi,

Good, the first thing to do is update your basic system to the latest version of the installed packages.

Normally your user is in the sudoers group which means you can do system maintenance. We'll know soon enough.

Go to System - Administration - Update Manager and start it. Click on Check to see if updates are available. Your system will prompt you for your password. Type it in and then OK.

When all is done, click on the button Install updates if any updates are listed in the window.

Kind regards,

Eric

Don't I need to set up my internet connection first ?
I know how to do that, but I have a small question. I'm using a secure one. I was wondering if there was a way to type the password in an encrypted way, because if I type it just like that it can be accessed in the internet options.

I thought you already were connected to the internet, sorry

Of course you need to be connected to the internet first in order to check for updates.

I'm not sure what you mean with 'type the password in an encrypted way'. And what do you mean by accessing the password in the internet options?

Normally you set up a connection using the network manager in Ubuntu. That one takes care of encrypting the password when communicating with your device. Can you tell me how you usually connect to the internet? Using wireless or cable? Do you have a DSL connection or other?

Kind regards,

Eric

wireless. There's an icon in the panel where I can choose my network. It then opens a window called wireless network authentification required.
I can type my password here.
If I do though, and then right click on the icon, then edit connections, then wireless, then the name of my connection, then a window appears intitled 'allow access' : allow application access to keyring ? The application 'nm-connection-editor (usr bin nm-connection editor) wants to acces the password for 'network secret for myconnection in the default keyring. If I (or someone else than me) then press 'allow once' and then go to 'wireless security' and 'show password', the password is visible, even though no admin password was asked during the whole procedure.

Hello,

I'm afraid someone else with more knowledge on Ubuntu has to kick in on that one. Normally I would say that your password is encrypted and only available to you. Of course if you leave your computer with a session open then anyone can get access to your password while you're away. If you lock your screen then they'd have to know your user password.

I'm not sure but I think that the connections are configured on per user basis, so if you create another user, he'll have to go through the same process to connect to your router. That new user will not have access to your data (unless if you put him in the sudoers group, then he can gain access).

Kind regards,

Eric

Ok nevermind let's proceed. I'm going to create a new thread because this one is becoming quite long, and the main problem has been fixed. Thanks a lot for your help Eric, and all the others too .