To perform agent maintenance on sysV init systems, such as Debian Wheezy, you will first need to stop the agent failsafe. This failsafe is designed to keep the agent running, even in the event of a serious error and will trigger even when the agent is being stopped as a normal service.
To disable the failsafe, open /etc/inittab in your favourite editor and comment out the line starting with ax:. Save the file and then issue the command init q as root, e.g. sudo init q
Once the failsafe is disabled, you can stop the agent using the normal service control commands
Once your maintenance is complete, please re-enable the failsafe by uncommenting the line you commented out earlier and run init q once more.