How to stop "aptd" from maxing out my CPU?

aptd is the service that installs software for Ubuntu Software Center and Update Manager. It runs as a separate, background process so that the installer can have root privileges while the GUI runs under your own user ID.

You should not stop aptd while software is installing: killing it will interrupt the installation, and possibly break the package system.

If you are not installing software and still see aptd using CPU time, then it's likely that you have the system set to automatically check for updates; those automatic update checks also use aptd.

In addition to the above information, if you notice that it is running for a long time - say an hour or more, it may be necessary to kill it. I ran into that when the Synaptic Package Manager appeared to be not responding for an extended period of time. After force closing it from the GUI, I found a couple instances of aptd and several other related processes running, and eventually I had to kill them.

In my case, I found that it was necessary to run the following commands to recover:

sudo dpkg-reconfigure -phigh -a
sudo dpkg --configure -a