User account disabled

After upgrading to Yosemite all accounts disabled

If you don't already have a current backup of all your data, you must back up before taking any of the steps below. Ask if you need guidance. You won't need the backup unless something goes wrong—which is always possible.

Step 1

Start up in Recovery mode. The OS X Utilities screen will appear.

Step 2

Take this step only if you use FileVault 2. Launch Disk Utility, then select the icon of the FileVault startup volume ("Macintosh HD," unless you gave it a different name.) It will be nested below another icon with the same name. Click the Unlock button in the toolbar and enter your login password when prompted. Then quit Disk Utility to be returned to the main screen.

Step 3

Select

Utilities ▹ Terminal

from the menu bar. In the window that opens, type this:

resetp

Press the tab key. The partial command you typed will automatically be completed to this:

resetpassword

Press return. A Reset Password window opens. Select your startup volume if not already selected. Pull down the menu labeled

Select the user account

and select

System Administrator (root)

Follow the prompts to set a password. It's safest to choose a password that includes only the characters a-z, A-Z, and 0-9. I suggest you write down the password. If you don't write it down and forget it, you'll have to start over from Step 1.

Select

 ▹ Restart...

from the menu bar.

Step 4

This step, like Step 2, applies only if you use FileVault. Log in as usual, then select

 ▹ Log Out...

from the menu bar, or press the key combination shift-command-Q. Don't restart. You'll be returned to the login screen.

Step 5

At the login screen, click Other... Enter "root" (without the quotes) in the Name field, and enter the password you set in Step 3 in the Password field. You should now be logged in as root. This is a potentially dangerous condition. Do nothing while logged in as root except as indicated below. You'll be fine as long as you don't deviate from the plan.

Open the Users & Groups preference pane. Create a new account and check the box marked

Allow user to administer this computer

You'll be prompted to restart. Do that and log in as the new user—not as root. Carry out the other steps suggested in the thread linked above.

Step 6 (optional, but recommended)

Follow the instructions in this support article under the heading "Disable the root user." You must authenticate in Directory Utility as "root" with the password you set in Step 3. Authenticating as another administrator won't work.