Login problems on Mac OS X Snow Leopard

These are notes from a tech support call with my parents last night, saved here for the next time stuff breaks.

If you’re running Mac OS X Snow Leopard (and possibly other versions), you may find you can’t log in. Symptoms are:

  • You click on your username and enter your password
  • The login screen is replaced by a blue screen for a short time
  • You are returned to the login screen.

After searching the interwebs I found Fixing a Mac OSX Leopard Login Loop Caused by Launch Services. It seems the problem is caused by corrupted cache files (which could be caused by the computer shutting down abruptly, or may just be “one of those things” that happens from time to time). This gave me enough information to come up with these “easy” steps to resolve it:

  1. Log in to the Mac as a different user*
  2. Press cmd-space to open Spotlight, type “Terminal”, and click on the Terminal application.
  3. Work out the broken user’s username by typing: ls /Users and look for the appropriate broken account name e.g. franksmith or janedoe.
  4. Find out the user ID of the user from the previous step by typing: id -u janedoe which will print a number something like 501
  5. Delete the user’s broken cache files. In the following command, be sure to substitute the correct username (in place of janedoe) and the correct user ID after the 023 (in place of the 501): su -l janedoe -c ‘rm /Library/Caches/com.apple.LaunchServices-023501.*’ (be very careful with this, you don’t want to delete the wrong things).
    • If you’re super-confident in figuring out backticks you could of course skip step 4 and instead of step 5 do: su -l janedoe -c ‘rm /Library/Caches/com.apple.LaunchServices-023`id -u janedoe`.*’
  6. Test by logging in to the troublesome user account.
Note that if you had any apps configured to launch at login, you may need to re-add these.

* This makes me think it’s good practice when setting up a Mac to always set up an extra user account, just in case stuff breaks.

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