I’ve been getting this error in WordPress, so I wasn’t using the auto-update functionality, which is a real time-saver. My problem was that WordPress was trying to write to `/tmp/` which is a no-no as my host (Segpub.net) uses Safe Mode. You can solve this issue by adding a couple of directives to your `wp-config.php` file, namely `WP_TEMP_DIR`. Adding these lines to `wp-config.php` fixed the problem for me:
putenv(‘TMPDIR=’ . ini_get(‘upload_tmp_dir’));
Thanks to the WordPress forums [for my answer][link].
[link]: http://wordpress.org/support/topic/291823?replies=2#post-1145649 ” WordPress › Support » Upgrade tries to write to root”