extlinux software package provides collection of bootloaders (Linux ext2/ext3/ext4, btrfs, and xfs bootloader), 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 extlinux
extlinux is installed in your system.
Make ensure the extlinux package were installed using the commands given below,
$ sudo dpkg-query -l | grep extlinux *
You will get with extlinux package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Utilities |
| Package | extlinux |
| Version | 3:6.03+dfsg-14 |
| Description | collection of bootloaders (Linux ext2/ext3/ext4, btrfs, and xfs bootloader) |
| Sub Section | Utils |