Sometimes you may run into an issue when installing multiple apps using yum where the process id is still locking the yum application. This most often occurs when running the command line yum with a graphical screen open rather then in a shell.
Here is the most common fix for this type of problem.
yum clean all
rpm –rebuilddb
On occasion you will have completed an update and the process will still lock the yum by having not cleaned the yum.pid file.
When you run yum clean all an output like another copy is running as pid <pid>
kill –9 <pid>
yum clean all
rpm –rebuilddb
If this still does not resolve it
sudo kill $(cat /var/run/yum.pid)
killall –9 safe_yum
yum clean all
rpm –rebuilddb