Standard ddev VMs have everything you need for most websites, but sometimes you might need an extra PHP module or command line tool. Ddev has made it easy to add additional packages to the VM. The VM is a Debian image (currently Debian 10 Buster), so you can add anything that is available in Debian's Apt package manager.
Just edit your .ddev/config.yaml file and add either the
dbimage_extra_package variable, depending on if you want to add the additional packages to the web VM or the database VM. Both variables are arrays. Ddev will automatically install these packages when you start the environment, so a
ddev restart is needed if you edit the config file after you've already started it.
For example, if you want to add the PHP imap extension and the rename command line tool to the web VM you can add this:
webimage_extra_packages: ["php-imap", "rename"]