I recently commented out that line to get a new kernel.
Once the Fed Up command from step 3 has completed without errors, reboot your system. grub), there will be a menu item “System Upgrade”, select that and press enter.
All the appropriate packages and upgrade tasks will now be completed automatically, and when completed you will be able to log in to your newly upgraded Fedora 21 Workstation.
During the upgrade process latest kernel got installed and the system needs reboot.
Fed Up is the new tool and it is the only official recommended way to Upgrade your fedora system now on. Select the System Upgrade (fedup) from the boot menu. Once upgrade completes, you can log into Fedora 18 system.
Here we are using YUM tool that simple updates your Fedora 17 packages from Fedora 18 repos. The Permissive mode required for upgrade, because during upgrade process several packages attempt to create users and groups.
If you not use this mode, you may end up with errors in yum update. You cannot upgrade older version – for example, upgrade from Fedora 16 to Fedora 18 with this script.
Since you have data backed up, and the DVD in-hand, the easiest way may just be to do a fresh install of F25 and then put your information back.
(I usually make a separate partition, to make this easier when I decide to do it.) We do have some suggestions for upgrading from old releases — see Upgrading from End of Life releases on the Fedora wiki.
If you are looking for clean Fedora 18 installation, then check out the following article that describes a Fedora 18 basic installation guide with screenshots.