After I moved to a new VPS (Ubuntu), I can't update the WordPress. When I click on the "Update Now" button, it shows upgrading progress messages and it shows "Welcome to WordPress 3.9" (Now I'm on 3.8.3), but after refresh the page, nothing happens. Again, I'm on the WordPress 3.8.3.
Then I deactivated all the plugins and again, I re-update the Wordpress. But nothing happened. I can only fix this issue after reboot the VPS. After the reboot VPS, when I log-in/visit the WP dashboard, it only shows upgrade message. However I can successful update plugins without rebooting.
My VPS running nginx, APC, pagespeed mod, Ubuntu 12.04.
What could be the reason for this matter?