Q: El Capitan Keychain Missing-Now cannot access Time Machine

Certain files have a property incorrectly set that will prevent them from being changed or deleted while the system is running. That property can only be removed in Recovery mode. If you don't feel that you can carry out this procedure yourself, please get someone more experienced to help you.

1. Back up all data. There are ways to back up a computer that isn't fully functional. Ask if you need guidance. Don't skip this step.

2. Disconnect all external storage devices.

3. Start up in Recovery mode. Select a language, if prompted. The OS X Utilities screen will appear. One of the options is to install OS X. That's not what you're going to do.

4. This step is only necessary if you use FileVault 2. If you don't know what FileVault is, you're not using it. Go to the next step. Otherwise, launch Disk Utility, then select the icon of the FileVault volume ("Macintosh HD," unless you gave it a different name.) It will be nested below another drive icon. 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.

5. Select Get Help Online. Safari will launch. While in Recovery, you'll have no access to your bookmarks, but you won't need them. Load this web page.

6. Triple-click anywhere in the line below to select it:

chflags norestricted /V*/*/L*/Keyc*/*

Copy the selected text to the Clipboard by pressing the key combination command-C.

7. Quit Safari. You'll be returned to the OS X Utilities screen.

From the menu bar, select

          Utilities ▹ Terminal

The Terminal application will launch. Paste into the Terminal window by pressing the key combination command-V.

Wait for a new line ending in a hash sign (#) to appear. Quit Terminal to be returned to the main screen.

8. Select

           ▹ Restart

from the menu bar.

9. This step must be carried out after the restart and while you're logged in as an administrator—not in Recovery mode. If you have only one user account, you are the administrator.

Select and copy this line as in Step 6:

sudo xattr -c /L*/Keyc*/*

Launch the built-in Terminal application in any one of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad and start typing the name.

Paste into the Terminal window as before. You'll be prompted for your login password. Nothing will be displayed when you type it. Type carefully and then press return. If you don’t have a login password, you’ll need to set one before you can run the command. You may get a one-time warning to be careful. Confirm. You don't need to post the warning.

If you see a message that your username "is not in the sudoers file," then you're not logged in as an administrator. Log in as one and start over.

Wait for a new line ending in a dollar sign ($) to appear below what you entered. You can then quit Terminal. Test.

If you want to preserve the data on the startup drive, and it's not already backed up, you must try to back up now, before you do anything else. It may or may not be possible. If you don't care about the data, you can skip this step.

There are several ways to back up a Mac that is not fully functional. You need an external hard drive or other storage device to hold the data.

1. Start up from the Recovery partition, from Internet Recovery, or from a local Time Machine backup volume (option key at startup.) Launch Disk Utility and follow the instructions in this support article, under “Instructions for backing up to an external hard disk via Disk Utility.” The article refers to starting up from a DVD, but the procedure in Recovery mode is the same. You don't need a DVD if you're running OS X 10.7 or later.

If you use FileVault 2, then you must first unlock the startup volume. Select its icon ("Macintosh HD," unless you gave it a different name.) It will be nested below another disk icon, usually with the same name. Click the Unlock button in the toolbar. Enter your login password when prompted.

2. If Method 1 fails because of disk errors, then you may be able to salvage some of your files by copying them in the Finder. If you already have an external drive with OS X installed, start up from it. Otherwise, if you have Internet access, follow the instructions on this page to prepare the external drive and install OS X on it. You'll use the Recovery installer, rather than downloading it from the App Store.

3. If you have access to a working Mac, and both it and the non-working Mac have FireWire or Thunderbolt ports, start the non-working Mac in target disk mode. A Retina MacBook (from 2015 or later) with a USB-C port can also be started in target disk mode and connected to another Mac using a USB cable and an adapter.

Use the working Mac to copy the data to another drive.

This technique won't work with USB (except on a Retina MacBook), Ethernet, Wi-Fi, or Bluetooth. Note that a Retina MacBook Pro (with Thunderbolt) is different from a Retina MacBook, and it can't be connected to another Mac via USB in target disk mode.

4. If the internal drive of the non-working Mac is user-replaceable, remove it and mount it in an external enclosure or drive dock. Use another Mac to copy the data.