Forbidden sign on reboot

ClaudioTomasoni wrote:

At reboot I get the forbidden sign on a MacBook Pro mid 2012 with an SSD.

The first time I pressed CMD + R and opened Recovery Mode from internet, ran Disk Utility and corrected an error on the EFI partition map. After the reboot everything worked fine.

Just to check I made a reboot and the problem was back again. Tried a number of things, including resetting the NVRAM, resetting, the SMC, rerun Disk Utility (no more errors detected).

Every time i go into Recovery Mode I'm able to just reboot and everything is fine. At the next reboot I still got the forbidden sign.

Looks also like randomly, after some power-off + power-on, the pc can boot back again in MacOS (something like 20% times ok and 80% ko).

I've disconnected the SSD and connected to a Linux PC so I could see SMART data for the disk. The disk looks in perfect shape with no errors and still 99% of available lifetime.

Also ran a Linux live distro on the MacBook on an external drive and performed a memory test with no errors. The live distro works perfectly with no errors.

Somebody please help.

If your Mac doesn't start up all the way

https://support.apple.com/en-us/HT204156

The prohibitory sign is an indication that, although your Mac appeared have the proper files to support booting, part way through the boot-up process, one of the important required files was found to be either damaged or the wrong version to boot your specific model Mac.

You can re-install the same version of MacOS, right on top of the instance you have installed, without losing your files or added Applications. By design, only System directories are bulk-erased. However, since over 350,000 files will be re-written, if you have any doubt about the integrity of your drive, this process could force it over the edge into failure.

It is always Prudent to have at least one backup copy before proceeding, if possible.