archfs software package provides virtual package provided by rdiff-backup-fs, 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 archfs
archfs is installed in your system.
Make ensure the archfs package were installed using the commands given below,
$ sudo dpkg-query -l | grep archfs*
You will get with archfs package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Virtual packages |
| Package | archfs |
| Version | |
| Description | virtual package provided by rdiff-backup-fs |
| Sub Section | Virtual |