Question: I am trying to install a .deb file in Debian 9 and I do this:

```
# sudo apt install ./respin-2.0.1.deb
Reading package lists... Done
E: Unsupported file ./respin-2.0.1.deb given on commandline

```

How do i fix this?

Answer: 
The package’s file name is invalid, which is why `apt` fails to process it. To fix this, proceed as follows (starting from scratch):

```
wget https://github.com/ch1x0r/LinuxRespin/raw/master/respin-2.0-1.deb
mv respin-2.0-1.deb respin_2.0-1.deb
apt install ./respin_2.0-1.deb

```

However this won’t work on Debian 9 because the dependencies can’t be satisfied; the package is only usable on Ubuntu (despite the author’s comments to the contrary).
Looks a lot like the file does not exist... Please post more details as per Stephen's comment.

If you are using a graphical session as root (which you should not), then you won't need sudo. The correct command to install your .deb is as you stated `dpkg -i <deb file>`.