# Linux : Pkg Mgmt : Index #### Overview - [dpkg](https://manpages.ubuntu.com/manpages/jammy/man1/dpkg.1.html) — Debian's low-level package manager; doesn't talk to repos or manage dependencies - apt tools — Debian's high-level package manager; builds on dpkg - [apt-get](https://manpages.ubuntu.com/manpages/jammy/man8/apt-get.8.html) + friends — "classic", crufty, prioritizes backwards compatibility - [apt](https://manpages.ubuntu.com/manpages/jammy/man8/apt.8.html) — newer, cleaner interface, prettier output, changes often, same functionality - man page doesn't show full set of commands and options - [aptitude](https://manpages.ubuntu.com/manpages/jammy/man8/aptitude-curses.8.html) — full-screen console UI on top of apt-get; old inactive - [Synaptic](https://wiki.debian.org/Synaptic) — ­old but still the best apt GUI; same features as apt-get CLI - not installed on Ubuntu by default (`apt install synaptic`) - [GNOME Software](https://gitlab.gnome.org/GNOME/gnome-software) — too simple and pretty, like a commercial store - installed by default on Ubuntu (`gnome-software`) - has plugins for Flatpak and Snap - Flatpak - Snap #### Ubuntu 22.04 Apps Four package-related apps appear when searching “software” in the “Activities” overview. | .desktop file | Name | Exec | | ---------------------------------------------------------------- | ------------------ | ----------------------------------------- | | `/usr/share/applications/org.gnome.Software` | Software | `gnome-software %U` | | `/usr/share/applications/software-properties-gtk` | Software & Updates | `software-properties-gtk` | | `/usr/share/applications/update-manager` | Software Updater | `/usr/bin/update-manager` | | `/var/lib/snapd/desktop/applications/snap-store_ubuntu-software` | Ubuntu Software | `/snap/bin/snap-store.ubuntu-software %U` | ###### software-properties-gtk - from package `software-properties-gtk` - man page says "Software Sources List editor" ###### update-manager - from package `update-manager` - created by Canonical - GUI that automatically checks for updates - "Settings" takes you to the "Updates" tab in `software-properties-gtk` ###### snap-store.ubuntu-software - takes you to `gnome-software` #### [Explanation From Reddit](https://www.reddit.com/r/debian/comments/9whj01/comment/e9q2bd2/) > **`.deb` Package Format** > > The `.deb` packaging format is the basic unit here, analogous to `.rpm` files. Packages come in two types, source and binary, but for simplicity I'm not going to touch on source packages. Binary packages are `ar` archives that contain two subarchives, `control.tar.gz` and `data.tar.XX` (usually `xz` nowadays), as well as a `debian-binary` file containing the package version. `control.tar.gz` contains, as it says, control files: `conffiles` lists configuration files, `control` lists the package information for `dpkg` to use, including dependencies and recommends, `md5sums` a list of file MD5 sums to verify files, and the `postinst` / `postrm` / `preinst` / `prerm` scripts that are executed when they sound like, which do things like create users, set up file ownership, start daemons, etc., and the inverse on removal. `data.tar.XX` contains a relative virtual filesystem starting from `/`, and containing the literal files that the package installs on the system, including the binaries, docs, config files/templates, and anything else. This is a big reason why you shouldn't be mucking about in places like `/usr/bin` or `/lib`, because `dpkg` ultimately manages all of these files for you. > > **dpkg** > > With the package format out of the way, we get to the lowest level user-accessible tool, `dpkg`. It works mostly like the rpm command in a practical sense, in that it takes a single `.deb` archive and installs it. `dpkg` keeps track of the installed packages in its database under `/var/lib/dpkg`, which also includes all the `control.tar.gz` files mentioned above (under `info/`), as well as a massive concatenation of all the `control` text files (in `available`). This directory is really the heart of `dpkg`'s knowledge of your system: any package you install is listed in here, along with all its control files, and this is the database that the `dpkg` too uses to know what you have installed. Managing the installed packages on your system is all it does: you give it that single .deb file, and, assuming all dependencies are satisfied, it will unarchive the `control.tar.gz` archive, add the `control` file to its database, execute the `preinst` script, extract the `data.tar.XX` file against `/`, then execute the `postinst` script. Voila, your package is installed. Removal happens in the reverse order but with a lot of `rm`, since the control files list what files are present in each package, and config files listed in `conffiles` are left alone by default (that's what `purge` does with `apt-get`/`apt`). `dpkg` only ever knows about packages that are actually installed, and you can for instance list installed packages with it (`dpkg -l`), or query the installed database in other more advanced ways. But for the most part, unless you're downloading an omnibus `.deb`, you never need to worry about `dpkg`. > > **apt-get** > > So `dpkg` is really low-level, so someone wrote the first layer of abstraction: apt-get , and it's cousin `apt-cache`. `apt-get`'s job is to scan repository mirrors, sort out dependency trees (by looking in the control files), download files, and install them in a correct and sensible order with `dpkg`. Another poster derisively called it a "wrapper", which isn't really true: `dpkg` has no knowledge of repositories, downloading, or anything else; this is all `apt-get`'s domain. Running its commands like `update`, `install`, and `remove` all trigger calls to `dpkg` eventually to actually do the grunt work of setting up the packages, but the command does a lot of its own stuff to handle dependencies, downloading over various protocols, and caching remote archive information for local use. > > **apt-cache** > > `apt-cache` is a cousin command that is used for querying information about the repositories via the locally cached copies fetched with `apt-get update`. This includes searching for packages, displaying information, etc. about packages that aren't yet installed. For most novices this was always a relatively rare command outside of searching but was useful for querying potential changes and showing package information. > > **apt-file** > > `apt-file` is another optional part of the toolstack which is really useful for searching packages for individual files, for instance "what package has `/usr/bin/foobar`". I highly recommend it if you ever ask that question! > > **apt-key** > > Finally in the "original APT toolstack", `apt-key` manages repository signing keys, which ensure cryptographic verification of any files you download via APT to protect against corruption and spoofing. In theory and (AFAIK) practice, they make sure you're downloading trusted packages from the people who gave you the keys (the Debian project master keys for the official repos, or a repo owner for a third-party APT repo). > > --- > > Now it's worth stressing that these 3 tools are OLD. All of them have existed for 20 or more years (APT from 1998, `dpkg` from 1994), and that age should tell you a lot about the era they were designed in. Though they've all grown over the years, fundamentally they're the same as they always have been, and can show their age in a lot of ways (like having multiple commands to interface with the APT system...). And I'd be remiss if I didn't mention the precursor to them, `dselect`, which was the original "package manager" written alongside `dpkg` back in 1994. > > --- > > **apt** > > `apt` is a newer, more functional, rewrite of the `apt-get`/`apt-cache` toolstack which aims to provide a single unified, modern, and "pretty" CLI command for interfacing with APT. It can do (as of at least Debian 9, as far as I can tell) everything those other commands do for 99.9% of administrative tasks. Personally I've jumped right in the front of this bandwagon, since I find the output far nicer and more unified. But fundamentally `apt` is the replacement for the other two going forward; just don't expect them to be deprecated any time soon. > > **aptitude** > > Finally `aptitude` is an ncurses GUI tool (with CLI commands) that works as an alternative to `apt-get`, originally released in 1999 as an alternative to `apt-get` and friends. It has a slightly different dependency parsing system, including a very lovely multiple-choice dependency resolution option which is useful sometimes. But from a basic level it does the same thing as `apt-get`/`apt-cache` and `apt`, just in a GUI format. Similarly, `synaptic` is the official desktop environment GUI tool to fit a similar niche.