APT.md

Overview

This plugin allows us to run scripts at various hook points in the apt process (yum calls these “slots” [*]).

Assuming you have an apt repo that contains this plugin:

1. apt install apt-plugin-universal-hooks # install a plugin called 'universal-hooks'
   • it is also known as yum-plugin-universal-hooks for convenience
2. add scripts to the appropriate place in /etc/apt/universal-hooks/ (manually, via a deb installation, etc)
   • script output is not hindered
   • if it exits non-zero it will have a warning to that effect
   • if it is not executable it will have a warning to that effect
   • for wildcard matches there is currently one argument passed to the script, --pkg_list=/path/to/randomlynamefile that has a list of packages being operated on, one per line of the file
     • non-wildcard matches will have no arguments
3. There is no mechanism in apt to disable this besides editing the configuration /etc/apt/apt.conf.d/apt-universal-hooks.conf.
4. /etc/apt/universal-hooks/ will remain if you apt remove apt-plugin-universal-hooks so that any scripts will be available when re-installed.

/etc/apt/universal-hooks/ structure

The main directory can have the following directories:

• A directory for arbitrary scripts to go in named after each apt hook point [*].

  • e.g. /etc/apt/universal-hooks/Post-Invoke/whatever.sh

• A directory called “pkgs” that will organize package specific scripts.

  • That directory contains directories named after the package in question, for example “perl”.
    • Those directories can contain directories, for arbitrary scripts to go in, named after each apt hook point [*].
      • Currently only “Pre-Install-Pkgs” and “Post-Invoke” are package specific.
    • e.g. /etc/apt/universal-hooks/pkgs/perl/Post-Invoke/whatever.sh

• A directory called “multi_pkgs” that will contains scripts for multiple packages.

  • Contains a directory named after each apt hook point [*].
    • Currently only “Pre-Install-Pkgs” and “Post-Invoke” are package specific.
    • Those directories can contain “wildcard” directories, for arbitrary scripts to go in.
      • a “wildcard” directory is a directory whose name contains __WILDCARD__ to stand for .* in Regexp parlance
      • If you want to match ^ea-.*$ you’d name this directory ea-__WILDCARD__
      • If you want to match ^.*-devel$ you’d name this directory __WILDCARD__-devel
      • If you want to match perl anywhere in the string: __WILDCARD__perl__WILDCARD__
      • If you want to match every package ever involved in a transaction, name it __WILDCARD__
        • This would be sort of weird though since you can get the same thing from /etc/apt/universal-hooks/Post-Invoke
      • e.g. /etc/apt/universal-hooks/multi_pkgs/Post-Invoke/ea-__WILDCARD__/whatever.sh
        • That script would run once at the end of a transaction if one or more packages that started with ea- were involved in the transaction.

Script Execution Order

The scripts are run in the order that your system glob() returns. While technically arbitrary it is typically lexicographically. That being the case we will prefix scripts with 3 digits and a hyphen, underscore, or period (e.g. 042-foo). If a script is not installed/updated/removed via a deb we should do the same number prefix but extend that with a cp- prefix (e.g. 042-cp-foo). Leaving a numeric gap between names will allow 3rdparties to do things in the spot they want.

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*Footnote: The hook point names and their descriptions are documented in man apt.conf under “HOW APT CALLS DPKG”.

At the time this was written that info was:

       Pre-Invoke, Post-Invoke
           … run before/after invoking dpkg(1).

       Pre-Install-Pkgs
           … run before invoking dpkg(1).

Note: There are similar APT::Update hook points too but those are not for install/upgrade/remove operations whcih is what universal-hooks is targeting.