How to fix the ‘untrusted_cert_title’ error when reinstalling macOS

Some Mac owners see untrusted_cert_title as an error when attempting to reinstall macOS. This problem arises when the Mac’s system clock is set incorrectly, and you can wind up in a chicken-and-egg problem: without macOS installed, there’s no straightforward way to set the clock, which would let you install macOS.

To create a secure connection, many encryption algorithms require an up-to-date clock. The encryption system wants to check whether a digital certificate that validates the integrity of a piece of software hasn’t yet expired. If the date embedded in the certificate is before the issuance date or after the expiration date, the software rightly balks—and macOS unfortunately spits out an error, as this eventuality wasn’t considered as far back as Mojave. (The problem may have been fixed since.)

To correct the date on your Mac, first determine your current date and time to format it for the command needed: you need the day of the month, the numeric month of the year (1 to 12), the current clock in hours and minutes using 24-hour format, and the last two digits of the current year.

In the U.S., and any country in which the day of the month customarily appears after the month, as in November 15, 2020, the format is day of month (1 to 31), month (1 to 12), hour (0 to 23), minutes (0 to 59), and year (20, as in 2020). All numbers that are single digits (like the 9th day of November) are padded with a 0 before them so that they are always two digits long. For example, 1:40 p.m. on November 15, 2020, would be formatted 1115134020.

In countries in which the day of the month comes first, you reverse the day of month and month of the year: 1511134020 in the above example.

Now follow these steps:

  1. Start the Mac up while holding down Command-R to boot into macOS Recovery.

  2. When the screen appears with a number of choices, ignore those and choose Terminal from the Utilities menu.

  3. Enter exactly the following and press Return, substituting the 10-digit date sequence you figured out above: date 1115134020

  4. Terminal will produce a line of output, if the command was entered correctly, that reads something like: Sun Nov 16 13:40:00 PST 2020.

  5. Choose Terminal > Quit.

  6. From the main recover window, click Reinstall macOS and follow prompts.

This Mac 911 article is in response to a question submitted by Macworld reader Tayla.

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