From time to time there are various problems after an update that result in the machine not getting all the way to the GUI prompt after an update. With a little bit of knowledge this becomes a less concerning issue, and can be quite easily fixed.
My most recent experiences of this were a few weeks ago, I ran a yum update - there was a new kernel package installed, but the graphics drivers from rpmfusion had not been released for the kernel. As a result the machine appear to hang during boot at the point when it should have started X11.
To help with these issues, the first thing I do when I install linux is edit the grub.conf file and change the timeout parameter from 0 to 3. This puts a 3 second pause in the startup, that allows you to press a key and get a boot menu up, that allows you to select an older kernel to boot. (You can also change the command line it uses to start the kernel). When you then have these problems you can simply use this menu to boot the previous kernel.
Even without this, you can switch to another terminal session on your console with CTRL-ALT-F2 (F3, F4...) CTRL-ALT-F1 will get you back. You can then log in and get a command line.
When things get really bad you will need to get out you linux install media and boot off that, to get a command line to perform the recovery.
No matter how you do it, once you have a command line you can fix your install.
Most often you can fix it by changing the default boot kernel to the previous one. Edit the /etc/grub.conf file - the line to edit the default=0, this is a reference to the first OS entry in the file, to boot using the second one change it to default=1.
Another technique is to use yum to roll back the changes, as described in yum - help I have broken my install
Another thing to consider if you are taking a lot of updates and often have problmes is to change the number of kernels that are allowed to be installed at one time. This is done in the /etc/yum.conf file, you can change the line installonly_limit=3 to a higher number. I usually set mine to 5 just to have a bit more buffer when things start to go wrong.
One of the realities of linux is that it is more stable a reliable on slightly older hardware that the drivers have had the bugs ironed out in them. When you are in the situation I have been lately where some of the hardware I have is only just supported in the latest release then this is when stability issues come to the fore.
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