Sometimes, you may try to run your puppet agent, and get an error like this:
# puppet agent --test
notice: Run of Puppet configuration client already in progress; skipping
If there is indeed another puppet agent running, it is simple enough to stop it and try again. However, what if this message appears, and there aren’t any other puppet instances running?
This happens because there is a flag stored in a file that didn’t get erased. Do this – but only if puppet is not in fact running:
# cd /var/lib/puppet/state
# rm -f puppetdlock
This will delete the lock, and puppet should start cleanly the next time. This tip works with puppet version 2.6.3.
UNIX Administratosphere 
see my last commen this is –enabling or –disabling the agent and quite a useful feature…
nice post .
Also – path to puppedtlock could be different from yours like for me it differs (i am on debian), we can use following commands – updatedb ; locate puppetdlock