I upgrade my Macbook to El Capitan as soon as I could, and have had very few issues with the release. On my iMac at work though, I’ve been putting off the upgrade since last October – due to time constraints and not wanting to mess anything in my dev environment up.
Today I tried to install El Capitan using the
Install OS X El Capitan.app installer.
I was greeted with this message. How could this be? The installer has simply been sat in my Applications directory since October, nothing has changed.
I used the following command to verify the integrity of the installer image:
hdiutil verify /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/SharedSupport/InstallESD.dmg
Which told me the image
is VALID. Alright, so there must be another cause?
Well I downloaded the installer in October 2015; In February 2016 Apple’s Signing Certificate expired. I actually encountered this issue when doing a fresh install of El Capitan on another Macbook earlier this year, the solution is simple: change the system date to earlier than February 2016.
That command changes the date to
October 21st 2015 at 12:00.
Alternatively you can use the Date & Time System Preferences pane:
Now you can run the installer without issue.
After OS X El Capitan has installed, it will set the date and time back to their correct values.
Now, rather than having to re-download a 7GB installer image, I just have to download a 2GB update!