Debian snapper apt script to include full apt command including arguments as snapshot description

00 Debian Snapper Update.md

This gist includes an enhancement to Debian's snapper package.

The current (as of 2023-07-23) snapper package includes an apt configuration that will automatically take snapper snapshots when you use apt to install/remove/etc. It will add use "apt" as the description of the pre/post snapshot.

With the below changes to the /etc/apt/apt.conf.d/80snapper file and associated dpkg-pre-post-snapper.sh file, snapper will include the full apt command, including the arguments, in the snapshot description.

For example:

$ sudo apt install funky
...

$ snapper list
...
525  | pre    |       | Sat 22 Jul 2023 11:32:47 PM EDT | root | number   | apt; apt install funky  |
526  | post   |   525 | Sat 22 Jul 2023 11:32:48 PM EDT | root | number   | apt; apt install funky  |

80snapper

# https://gist.github.com/imthenachoman/f722f6d08dfb404fed2a3b2d83263118
# https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=770938

DPkg::Pre-Invoke { "/path/to/dpkg-pre-post-snapper.sh pre"; };
DPkg::Post-Invoke { "/path/to/dpkg-pre-post-snapper.sh post"; };

dpkg-pre-post-snapper.sh

#!/bin/bash

# this script is an enhancement of https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=770938

# we need to work up the process tree to find the apt command that triggered the call to this script
# get the initial PID

PID=$$

# find the apt command by working up the process tree
# loop until
# - PID is empty
# - PID is 1
# - or PID command is apt
while [[ -n "$PID" && "$PID" != "1" && "$(ps -ho comm "${PID}")" != "apt" ]] ; do
    # the current PID is not the apt command so go up one by getting the parent PID of hte current PID
    PID=$(ps -ho ppid "$PID" | xargs)
done

SNAPPER_DESCRIPTION="apt"

# assuming we found the apt command, get the full args
if [[ "$(ps -ho comm "${PID}")" = "apt" ]] ; then
    SNAPPER_DESCRIPTION="$(ps -ho args "${PID}")"
fi

# main event

# source /etc/default/snapper if it exists
if [ -e /etc/default/snapper ] ; then
    . /etc/default/snapper
fi

# what action are we taking
if [ "$1" = "pre" ] ; then
    # pre, so take a pre snapshot

    # if snapper is installed
    # and if snapper snapshots are not being disabled using the DISABLE_APT_SNAPSHOT variable
    # and if /etc/snapper/configs/root exists
    if [ -x /usr/bin/snapper ] && [ ! x$DISABLE_APT_SNAPSHOT = 'xyes' ] && [ -e /etc/snapper/configs/root ] ; then
        # delete any lingering temp files
        rm -f /var/tmp/snapper-apt || true

        # create a snapshot
        # and save the snapshot number for reference later
        snapper create -d "${SNAPPER_DESCRIPTION}" -c number -t pre -p > /var/tmp/snapper-apt || true

        # clean up snapper
        snapper cleanup number || true
    fi
elif [ "$1" = "post" ] ; then
    # post, so take a post snapshot

    # if snapper is installed
    # and if snapper snapshots are not being disabled using the DISABLE_APT_SNAPSHOT variable
    # and if the temp file with the snapshot number from the pre snapshot exists
    if [ -x /usr/bin/snapper ] && [ ! x$DISABLE_APT_SNAPSHOT = 'xyes' ] && [ -e /var/tmp/snapper-apt ]
    then
        # take a post snapshot and link it to the # of the pre snapshot
        snapper create -d "${SNAPPER_DESCRIPTION}" -c number -t post --pre-number=`cat /var/tmp/snapper-apt` || true

        # clean up snapper
        snapper cleanup number || true
    fi
fi

Thanks. I submitted a PR to their repo but nothing ever happened with it. :/

Did you submit this to Debian Salsa for inclusion in the next release? I can if you haven't. https://salsa.debian.org/debian/snapper/

I feel like I had submitted it somewhere but I can't remember where now. How do I submit this for Salsa?

You'd have to create a Salsa account and figure out where it fits in the Debian package (which isn't immediately obvious to me without spending more time on it). It's a simple change somewhere but I don't know where after looking for 15 minutes.

Hi @imthenachoman — I forked this gist and have substantially expanded dpkg-pre-post-snapper.sh. I’m now preparing to move my version into a standalone, maintained GitHub repository.

I’m trying to document the project’s origin and licensing correctly. From the earliest revision of this gist, it looks like dpkg-pre-post-snapper.sh may have been based on Debian’s inline Snapper APT-hook logic from 80snapper, moved into a separate script and enhanced with process-tree detection and full-command descriptions.

Is that how the script originated, or was it adapted from another source?

Debian’s Snapper packaging is licensed under GPL-2. If the script originated as an adaptation of Debian’s hook, do you also consider your modifications in this gist to be distributed under GPL-2?

I want to preserve the correct licensing and attribution to Debian’s original work, Debian Bug #770938, your enhancements, and any other source that may have been involved.

My current fork is here:
https://gist.github.com/mcsgeek/c74cc7925f9a345298836c2df137194a

Wow! That is great. Thank you for doing this!

Is that how the script originated, or was it adapted from another source?

Yes. 80snapper had a command to do the snap. I replaced it with an external script.

Debian’s Snapper packaging is licensed under GPL-2. If the script originated as an adaptation of Debian’s hook, do you also consider your modifications in this gist to be distributed under GPL-2?

Yes

Do you need me to add license to my stuff anywhere?

Can we get this put into Debian Salsa instead of floating around the web/separate Github repo so these great changes will become part of the official Debian repositories and help everyone in the future?

I tried. I even submitted a PR to them but nothing ever happened. I assume it's cause I don't have enough clout for anyone to listen to me. :P

https://salsa.debian.org/debian/snapper/-/merge_requests/2

Hi @imthenachoman,

Thank you for the clarification and for confirming the licensing. That answers exactly what I needed to know.

I really appreciate the work you put into this. Your idea of moving Debian's inline 80snapper hook into a standalone script and adding process-tree detection provided a much stronger foundation to build on.

My version has grown quite a bit beyond the original gist with additional package manager detection, improved snapshot descriptions, locking, duplicate snapshot prevention, and various reliability improvements, but your work was the starting point that made it possible.

I'll make sure the project documentation properly credits Debian's original 80snapper hook, Debian Bug #770938, and your contributions so the project's history is preserved accurately.

Regarding your question about the license, your confirmation here is exactly what I was hoping to document. If you ever decide to add a GPL-2 license notice to the gist itself, it would certainly make the licensing explicit for future readers, but I don't think it's necessary for my project. Your response here gives me the clarification I was looking for.

I also saw your previous Salsa merge request. That's unfortunate that it never gained any traction. My immediate goal is to get the standalone repository cleaned up, documented, and well tested. If it proves useful, I'd certainly like to see the improvements make their way back into Debian one day.

Thanks again for taking the time to respond and for sharing the original work with the community. I hope you'll take a look at the finished repository once it's published.

That’s a real shame about the Salsa submission. I looked a while back didn’t and see any activity in that area for Snapper. I suspect it was that - just that there aren’t enough humans to pay attention to it. I’d say once this is tested it’s worth trying again. It’s a major improvement in functionality.

Hi @imthenachoman,

Thanks again for taking the time to answer my questions and clarify the project's origins and licensing. It was a huge help.

I've now published the standalone project:

https://github.com/mcsgeek/dpkg-pre-post-snapper

I've done my best to preserve the project's history and properly acknowledge Debian Bug #770938, Debian's 80snapper implementation, and your work that moved the hook into an external script and introduced process-tree detection.

Thanks again for your original work and for helping me get the attribution and licensing right.

This is great! Thank you. And great job. It’s a lot more useful now.