[CentOS] Yum hangs while doing update

On 07/01/2013 01:16 PM ken wrote:
> About thirty minutes ago I started an update.  Everything downloaded
> fine.  But when it came to "Running Transaction", it hung:
>
> ....
> Running rpm_check_debug
> Running Transaction Test
> Finished Transaction Test
> Transaction Test Succeeded
> Running Transaction
>     Updating       : xulrunner
>       1/18
>
>
> And there it sits still.
>
> There's plenty of disk space.  The load on the CPU is under 1.0.  There
> is some disk activity, but no way so much as to cause anything to hang
> and no major writing related to yum.  Disk reads are just about null,
> except just now when I grep'ed for something to make sure that the disk
> could be read.  I'm not using even half of the available RAM.
>
> Anyone else run into this problem?

I had to kill yum to end the process.  Then I tried again, less 
ambitiously and it hung again, this time earlier in the process:

  # yum -d 8 update firefox
Loading "aliases" plugin
Loading "allowdowngrade" plugin
Loading "changelog" plugin
Loading "downloadonly" plugin
Loading "fastestmirror" plugin
Loading "filter-data" plugin
Loading "kernel-module" plugin
Loading "keys" plugin
Loading "kmod" plugin
Loading "list-data" plugin
Loading "merge-conf" plugin
Loading "priorities" plugin
Loading "security" plugin
Loading "tsflags" plugin
Loading "verify" plugin
Running "config" handler for "aliases" plugin
Running "config" handler for "allowdowngrade" plugin
Running "config" handler for "changelog" plugin
Running "config" handler for "downloadonly" plugin
Running "config" handler for "filter-data" plugin
Running "config" handler for "keys" plugin
Running "config" handler for "list-data" plugin
Running "config" handler for "merge-conf" plugin
Running "config" handler for "priorities" plugin
Running "config" handler for "security" plugin
Running "config" handler for "verify" plugin

And there it hangs now.