yum lock error ::

Existing lock /var/run/yum.pid: another copy is running as pid [pid number].
Another app is currently holding the yum lock; waiting for it to exit...

Example :

[root@server /]# yum install [service name]
Loaded plugins: fastestmirror
Existing lock /var/run/yum.pid: another copy is running as pid 20360.
Another app is currently holding the yum lock; waiting for it to exit...
  The other application is: yum
    Memory :  19 M RSS (396 MB VSZ)
    Started: Sun Mar  6 21:06:51 2011 - 00:29 ago
    State  : Traced/Stopped, pid: 20360

Please hit ctrl-c; that’s the key combination to kill any currently running process in a bash shell or terminal.

Exiting on user cancel.

Solution 1:
To remove the pid, please run command rm -f and follow with yum.pid path and [pid number]

[root@server /]# rm -f /var/run/yum.pid 20360

Solution 2:
Find out what is the locking up yum by running:

[root@server /]# ps aux | grep yum

Please take note on the [pid number] of the process and run this command to kill the process:

[root@server /]# kill -9 [insert pid]