This post is about something I tried when I was working on an offline Debian upgrade project. While it didn’t ultimately provide the solution to that project, it did open up a wonderful possibility. To kick this post off, we must have a talk about dependencies, and since that can become mind numbing quickly, I’m only going to gloss over that topic. We’ll talk about what this script does, how to use it, and then turn you loose.

Dependencies _> The Underworld

Dependencies are what the majority of packages or projects rely on to work. Think of it like a base foundation that many people contribute to. This is usually in the form of “lib” or library packages. Other developers will use this pre-written code in their projects, and that’s the end of it right? Not really. Actually, a single project can use dozens to hundreds of dependencies all stacked upon one another like a pyramid of code. This can quickly become a large security issue as the more a system has installed the more dependencies it relies upon. It is at that point that the system’s security becomes more and more dependent (no pun intended) upon every dependency. In other words, the weakest link in any program is the amount of dependencies it uses as much as a chain is only as strong as its weakest link. 

So there’s some of the ugly; let’s talk about the bad for a second. Let’s say you’ve gotten entangled in a project that needs some offline packages installed. Where do you start?

The Journey

For me I started at the online Debian package repository. I needed to download Java for another project. Needless to say you quickly find that you need at least four packages right off the bat.

openjdk-8-jre.deb openjdk-8-jre-headless.deb openjdk-8-jdk-headless.deb openjdk-8-jdk.deb

Yikes! Each package has even more dependencies. And those have even more dependencies. Wouldn’t it be nice if you could just get all the packages and the dependencies without the downloads?

The Solution

I was getting desperate for a solution. Downloading package after package after package is the worst. I have a life and better things to do. Enter salvation in the form of ingenius scripting from OSTechNix. Simply make a folder of the package you wish to download and get cracking.

Here’s the code again below for reference. We’ll step through it.

#!/bin/bash

read -p "What pkg are you building?: " pkg

##Code attribution for the code below
##https://www.ostechnix.com/download-packages-dependencies-locally-ubuntu/

for i in $(apt-cache depends $pkg | grep -E 'Depends|Recommends|Suggests' | cut -d ':' -f 2,3 | sed -e s/'<'/''/ -e s/'>'/''/); do sudo apt-get download $i 2>>errors.txt; done

The Code

I’m going to assume you have made your directory and you are ready to proceed to the next step. If you want you can copy the script above and put it in your /usr/local/bin which will make your script available in your system paths. Make sure it’s executable. I usually run my scripts as root on test systems, so for your system you may wish to use “sudo” in front of whatever you named this script.

read -p "What pkg are you building?: " pkg

This is the first line I added, and it offers some bonuses. You can put as many different packages as you want, spaced out of course. It’s a simple input line for bash with the variable at the end. As you can see, we use that later.

for i in $(apt-cache depends $pkg | grep -E 'Depends|Recommends|Suggests' | cut -d ':' -f 2,3 | sed -e s/'<'/''/ -e s/'>'/''/) 
     do 
        sudo apt-get download $i 2>>errors.txt
     done

I’m going to skip over the code attribution because I think that’s rather self-documenting. The rest of this code starts with a standard for loop. What follows next is a calling of the apt-cache command and the depends command for the package ($pkg, told you we’d use it later) you want to download. Then we pipe to grep, doing a little cutting, run sed (which does some awesome clean up), and then we finally get to downloading the packages.

Wrapping it up

Before you start running this script, make sure you’re in the actual folder you created. Otherwise you could end up with a lot of deb packages everywhere. Not to worry if you did though. Here’s some shortcode to get things cleaned up. We’ll assume you’re in the /tmp/ folder, and you ran, for example, the java packages I listed out earlier. What a mess!

cd /tmp/
##gotta get in the tmp directory first right?
##remember the java folder (package folder) I made?
mv *.deb /tmp/java

And boom. You’re all good. Hope it helps.