initramfs-tools software package provides generic modular initramfs generator (automation), you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install initramfs-tools
initramfs-tools is installed in your system.
Make ensure the initramfs-tools package were installed using the commands given below,
$ sudo dpkg-query -l | grep initramfs-tools *
You will get with initramfs-tools package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Utilities |
| Package | initramfs-tools |
| Version | 0.125 |
| Description | generic modular initramfs generator (automation) |
| Sub Section | Utils |