What are some problems that could cause Magento to redirect to /downloader/ (Installation wizard)

Question

I have a site that has been running fine for awhile. Ran an SVN update after making some changes in the development environment. Now the site keeps redirecting to the Installation Wizard (/downloader/) No matter what I do. Checked and double checked database settings - all seems good. Can anyone tell me what other problems could have this result? I just wish it would give me a freaking error so I could more easily troubleshoot the actual problem.

Answer 1

If you check the index.php file you will see the following...

$mageFilename = 'app/Mage.php';
$maintenanceFile = 'maintenance.flag';

if (!file_exists($mageFilename)) {
    if (is_dir('downloader')) {
        header("Location: downloader");
    } else {
        echo $mageFilename." was not found";
    }
    exit;
}

That is to say, if there is no app/Mage.php file and there is a downloader folder, it will redirect to it.

Answer 2

Check is your app/etc/local.xml file found and readable (644) by the webserver, this should solve the problem.

Answer 3

I deleted both the /var/cache and /var/session directories. It appears to have solved the problem.