Hello and thanks for your ideas.
I was finally able to reinstall OS X El Capitan under OS X El Capitan with a bootable key.
I don't know yet if it came from my key (16gb and which works as a USB support) but I remade a boot system on a key (32gb but I don't think the size is important beyond 16gb) and under a Terminal method (see tutorial Creating a bootable installer for macOS - Apple Support (FR)) with the command line:
sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app
I first disconnected my MP from the internet by unplugging the cable and changed the date in System Preferences (03/02/2018 here) and unchecked the automatic date setting.
Then I applied the method to create my key. The DMG is that of version 15G31. (I don't know if this matters)
The Mac Os X DMG was put in the trash and deleted.
Once finished I restarted with the alt key (Option). The boot menu displays the key. Click on it and the installation program starts. And normally goes to its end.
For info I tried to redo the installation with the key that works but having reconnected the ethernet cable and put the connection and the normal date back.
The installation cannot complete. A message appears at the end of the installation:
"Unable to verify this copy of the Install OS X El Capitan application. It may have been damaged or altered during installation."
However, it is still impossible to install via Recovery and therefore the internet, the result is always the same:
"An unexpected error occurred while signing in. The server gave an error during download: 403 Forbidden."
A user ( Djams ) suggested two hypotheses to me:
1-a problem related to my box: blaklisted error of my IP. (quite possible)
2-by an interesting repost that gave me an idea to get around the problem by going through a local server where the installer would be stored, therefore to configure my machine so that in mode N at startup it goes to the server. (I summarize) And can install it. But I am not savvy enough to try, you have to create a local subnet with another machine that can act as a server if I have followed a little.
Here is the result of this research.
Thank you and have a nice day
Olivier
PS: to complete and open to other old OS here are 3 points to read carefully:
www.theobouzige.fr
- How to fix an error that occurs when you want to install old versions of Mac OS X on necessarily old Macs that do not support the latest Mac OS X Sierra or Yosemite. The error occurs when launching the application, indicating for example with El Capitan "Unable to verify this copy of the Install OS X El Capitan application. It may have been damaged or altered during installation." To correct this, the solution is very simple and as strange as it may seem, just set your Mac to the release date and time of the system you want to install.
For El Capitan it is: January 9, 2016 at 8:00 p.m.
For OS X Mavericks: October 22, 2013 at 8:00 p.m.
For OS X Yosemite: October 16, 2014 at 8:00 p.m.
Disconnect the internet first.
Go to "Utilities" then "Terminal" and enter in this order:
date {month}{day}{hour}{minute}{year}
Example: date 0318125013
Then validate by pressing "Enter".
Or in System Preferences uncheck the automatic date setting, and change the date and time.
- Disable SIP just in case.
System Integrity Protection (SIP)
To disable SIP, restart your Mac on the recovery partition, holding down the ⌘ and R keys at startup. Launch the Terminal with the Utilities > Terminal menu, then type the command:
csrutil disable
The message Successfully disabled System Integrity Protection. Please restart the machine for the changes to take effect should appear to confirm the operation.
Restart your Mac: SIP is now disabled. For the sake of it, you can always check it in the Terminal with the command:
csrutil status
The message System Integrity Protection status: disabled appears.
To reactivate SIP. After restarting your Mac on the recovery partition and launching the Terminal, this time enter the following command:
csrutil enable
- if you want to downgrade your OS, i.e. go from El Capitan to Yosemite on your HD, before finalizing the installation you will have to go through Utilities - Disk Utility and erase the disk on which El Capitan is located otherwise the installer will refuse to do it by indicating
