Chapter in this post:
A few days ago, my reader Peter wrote to me that he received a strange error message when installing OS X El Capitan and after that he could only press "OK", which aborts the installation. The exact wording of the error is:
This copy of the Install OS X El Capitan application can't be verified. It may have been corrupted or tampered with during downloading.
At first it sounds like you've caught a contaminated download that may contain malware, but I can give the all-clear here. This error message usually occurs when installing OS X El Capitan or OS X Yosemite because the Mac has not set the correct time or date.
This error is also not uncommon:
An error occurred while preparing the installation. Try running again.
Sometimes these errors can also be fixed by simply restarting your Mac and starting the installation from scratch. And to rule out the unlikely (but possible) case that the OS X installer is damaged, you should also try a newly downloaded installer.
However, if it does not run properly the second time, then it could be that changing the system time and date on the Mac is the solution.
The easiest way to set the system time and date on your Mac is to use the "Set the date and time automatically" option. This can be found under
Apple menu (top left)> System Preferences> Date & Time
However, this only works if the Mac is connected to the Internet and can get the current time from a timeserver such as time.euro.apple.com.
If the Mac is not connected to the Internet and you have no access to the system settings, which can also be used to set the time manually, then you can only use the terminal. This can also be called up in the boot menu of the OS X installation by opening the "Utilities" or "Utilities" menu and selecting "Terminal" there.
If you now enter the command "date" at the command prompt (confirm with Return), the output is the current system time of the Mac. If you notice a deviation from the actual time or date, you can be almost certain that the error message can be eliminated by setting the correct time.
The year is particularly important for the OS X installer. If the current system year is before the year in which the corresponding OS X version was released, this is an indication for the installer that something is wrong here.
There are two ways to supply the Mac with the current time:
Again, this assumes an internet connection, but it would be the most elegant solution to the problem. To do this, enter the following command in the terminal:
ntpdate -u time.euro.apple.com
Set the date and time with the terminal
If the Mac has no Internet, you can still set the date and time with the terminal. The corresponding command is:
That looks a bit confused, but has a simple explanation because the letters must be replaced by the corresponding numbers. So in English Month Date Hour Minute Year. Everything is entered in one piece and without spaces, whereby each numerical value is always two-digit:
That is, for September 7, 2019 at 16:43 p.m. the command would look like this:
If you have set the time again this way (don't forget to return!), You can close the terminal and start the installation process again and it is highly likely that the Mac will no longer throw these strange error messages.
If the error messages really continue to be thrown, it could indeed be because something was changed in the installer. For this reason, I recommend that you only load the installers for OS X and macOS from trustworthy sources. This does NOT include buying a DVD on eBay. A reader has already reported here that he received a self-burned DVD that didn't even work. Another had been sent a DVD on which the virus scanner even hit.
Likewise, I would keep my hands off dubious-looking download sites. In case of doubt, you only catch malware and viruses here and you have a system that has been completely provided with gateways for hackers.
Perhaps you have friends with a Mac who still have an old system at their disposal. For years I've kept all Apple systems on an external hard drive in case I need them again. At this point perhaps the reference to my article with the download options for old macOS / OS X systems.
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Jens has been running the blog since 2012. He appears as Sir Apfelot for his readers and helps them with problems of a technical nature. In his free time he drives electric unicycles, takes photos (preferably with his iPhone, of course), climbs around in the Hessian mountains or hikes with the family. His articles deal with Apple products, news from the world of drones or solutions for current bugs.