When installing Webmin, I’ve sometimes come across an error installing a dependency package, apt-show-versions:

Setting up apt-show-versions (0.22.7) ...
** initializing cache. This may take a while **
FATAL -> Failed to fork.
dpkg: error processing package apt-show-versions (--configure):
subprocess installed post-installation script returned error exit status 100
dpkg: dependency problems prevent configuration of webmin:FATAL -> Failed to fork.

This is caused by the fact that apt-show-versions can’t read compressed index files. Thankfully, the solution is quite simple:

First, we need to tell APT not to compress the index. To do this we create an entry in a file called /etc/apt/apt.conf.d/02compress-indexes:

sudo nano /etc/apt/apt.conf.d/02compress-indexes

If the file is empty (mine was), simply put this line in it:

Acquire::GzipIndexes "false";

if the file has some text, check if this parameter is in there as “true” and if so change to false. If it’s missing, just add it.

Then, we need to delete the existing indexes and re-download them:

sudo rm /var/lib/dpkg/info/apt-show*

followed by

sudo apt-get update

Finally, we just need to complete the installation:

sudo apt-get -f install webmin

And job done.