A strange thing happened the other day. One day, I could log into WordPress and everything was fine. The very next day, when I loaded up the /wp-admin page, I just got a blank screen. I tried going directly to wp-login.php, but again, just a blank screen. I checked the Apache error logs, and there wasn’t anything strange in there. I then checked the PHP error logs and found:
[08-May-2013 19:51:44 UTC] PHP Fatal error: Unknown: Failed opening required '/path/on/server/web-root-dir/wp-login.php' (include_path='.:/usr/local/php:/usr/share/pear') in Unknown on line 0
I checked, and wp-login.php was exactly where it was supposed to be. However, upon closer inspection, the file permissions were completely cleared out for this file. I reset the file permissions using:
chmod 644 wp-login.php
I went refreshed the wp-admin page, and everything worked again. Still investigating why this file permission changed occurred, but wanted to document what I had done to fix it while I still remembered.