How to install SWI-Prolog on Debian 13 Trixie without dying trying.

# Update the package index so APT knows the latest versions
# available in the configured repositories.
sudo apt update

# Install the main metapackage. Bring with you:
#   swi-prolog-core — the compiler core
#   swi-prolog-core-packages — base packages (clib, ssl, http, etc.)
#   swi-prolog-nox — binaries without X11 dependencies
#   swi-prolog-x — XPCE, the legacy GUI based on X11
# If you only work on server or terminal, use swi-prolog-nox instead.
sudo apt install swi-prolog

# Only the interpreter, without any dependency on the graphical environment.
# Ideal for servers, scripts, or containers.
sudo apt install swi-prolog-nox

# Everything included: core + GUI + Java (JPL) + ODBC + BerkeleyDB + documentation.
sudo apt install swi-prolog-full

# HTML documentation and examples (can be installed along with any variant).
sudo apt install swi-prolog-doc

# Java↔Prolog (JPL) Interface. Requires JDK installed.
sudo apt install swi-prolog-java

# Shows the installed version and exits.
swipl --version

# Open the interactive interpreter. Write halt. to go out.
swipl

# Update (it is normally done with the complete system).
sudo apt update && sudo apt upgrade

# Uninstall the interpreter and its related packages.
# The 'swi-prolog*' pattern covers all sub-packages.
sudo apt purge 'swi-prolog*'

# Clean up dependencies that were orphaned after uninstallation.
sudo apt autoremove

# Install the Flatpak client from the Debian repositories.
sudo apt install flatpak

# Add Flathub as a remote repository.
# --if-not-exists prevents an error if it was already set.
# The .flatpakrepo file downloads the GPG key from Flathub and registers it.
flatpak remote-add --if-not-exists flathub \
    https://dl.flathub.org/repo/flathub.flatpakrepo

# Install SWI-Prolog from Flathub.
# The app identifier is org.swi_prolog.swipl.
# This downloads the Freedesktop SDK runtime if you don't have it already,
# plus SWI-Prolog's own files (several hundred MB in total
# on first installation).
flatpak install flathub org.swi_prolog.swipl

# Explicit way: launches swipl (console interpreter) inside the sandbox.
# --command=swipl select the binary inside the Flatpak
# instead of the default launcher (which opens swipl-win).
flatpak run --command=swipl org.swi_prolog.swipl

# For the GUI window:
flatpak run org.swi_prolog.swipl

# Open your Bash configuration file with your editor.
# Change ~/.bashrc to ~/.zshrc if you use Zsh.
nano ~/.bashrc

# Alias ​​to invoke SWI-Prolog (Flatpak) in the current terminal,
# without it opening a separate GUI window.
alias swipl='flatpak run --command=swipl org.swi_prolog.swipl'

# Optional alias for the GUI window when you do want it.
alias swipl-win='flatpak run org.swi_prolog.swipl'

source ~/.bashrc

# With the alias active, this already works as expected.
swipl --version

# Updates all Flatpaks installed on the system, including SWI-Prolog.
flatpak update

# Uninstall SWI-Prolog only.
flatpak uninstall org.swi_prolog.swipl

# Also delete runtimes that were left unused.
flatpak uninstall --unused

# Base tools: C/C++ compiler, CMake, Ninja (faster alternative
# to make), pkg-config to locate system libraries.
sudo apt install -y \
    build-essential cmake ninja-build pkg-config git

# Terminal interface and line editing libraries.
# ncurses-dev — terminals and menus in text mode.
# libedit-dev — line editing (alternative to readline).
sudo apt install -y \
    ncurses-dev libedit-dev

# tcmalloc – Google memory allocator. Reduces memory usage
# multithreaded applications. Improves performance on servers.
# libgmp-dev: arbitrary precision arithmetic (large integers,
# rational numbers). Without this dependency, SWI uses internal (slower) LibBF.
sudo apt install -y \
    libgoogle-perftools-dev libgmp-dev

# SSL/TLS for the library(ssl) module and HTTPS connections.
sudo apt install -y libssl-dev

# ODBC: interface for relational databases via library (odbc) / CQL.
sudo apt install -y unixodbc-dev

# Compression and file formats.
# zlib1g-dev — basic compression.
# libarchive-dev — read/write .tar.gz, .zip, etc. (library(archive))
#                  also required by pack_install/1.
sudo apt install -y zlib1g-dev libarchive-dev

# UUID, BerkeleyDB and PCRE2.
# libossp-uuid-dev — library(uuid). Without this it uses pure Prolog implementation.
# libdb-dev — library(bdb), interface to BerkeleyDB.
# libpcre2-dev — library(pcre), PCRE2 regular expressions.
sudo apt install -y libossp-uuid-dev libdb-dev libpcre2-dev

# YAML and Unicode text processing.
# libyaml-dev — library(yaml).
# libutf8proc-dev — library(unicode), Unicode normalization.
sudo apt install -y libyaml-dev libutf8proc-dev

# Python 3 and embedding interface (Janus: call Python from Prolog
# and vice versa). Also required for the Python MQI server.
sudo apt install -y python3 libpython3-dev

# Dependencies for the GUI (XPCE with SDL3 + Cairo + Pango).
# As of SWI-Prolog 9.3.26 the GUI no longer uses X11 directly:
# uses SDL3 for windows, Cairo for vector drawing, Pango for text.
# libsdl3-dev — windows, keyboard/mouse events.
# libsdl3-image-dev — loading images in the GUI.
# libcairo2-dev — 2D vector rendering.
# libpango1.0-dev — text rendering with fonts.
# Debian 13 includes SDL3 natively, unlike Debian 12.
sudo apt install -y libcairo2-dev libpango1.0-dev libsdl3-dev libsdl3-image-dev

# Java (JPL: Java↔Prolog bidirectional interface) and its test suite.
# junit4 is required since version 8.1.29 for JPL testing.
sudo apt install -y default-jdk junit4

# Clone the development repository. --recurse-submodules is required:
# SWI-Prolog has its packages as independent Git submodules
# (clib, ssl, http, pengines, etc.) and without this option they would be empty.
git clone --recurse-submodules https://github.com/SWI-Prolog/swipl-devel.git

cd swipl-devel

# Lists the latest stable version tags (even version number = stable).
# The versions with the odd minor number (9.1.x, 9.3.x) are development.
git tag -l 'V*' | grep -E 'V[0-9]+\.[02468]+\.' | sort -V | tail -10

# Check out the chosen tag. Replace V9.2.9 with the version you prefer.
git checkout V9.2.9

# Updates the submodules to the state that corresponds to that tag.
git submodule update --init --recursive

# Create the build directory. By convention it is called "build".
# CMake never touches the source tree - all generated files
# (Makefiles, objects, binaries) go inside this directory.
mkdir build && cd build

# Configure the build.
#
# -DCMAKE_BUILD_TYPE=PGO
#   Profile Guided Optimization: Compiles the system twice.
#   First pass: instrumented to collect execution statistics.
#   Second pass: use those statistics to optimize branch prediction,
#   inlining, etc. Produces an interpreter ~30-40% faster than Release.
#
# -DCMAKE_INSTALL_PREFIX=/usr
#   Defines where the files will be installed (binaries in /usr/bin,
#   libraries in /usr/lib, etc.). This value is recorded in the .deb
#   that CPack generates, so when APT installs the package the files
#   they will go exactly to /usr. Use /usr/local if you prefer not to mix with
#   system packages.
#
# -G Ninja
#   Use Ninja as the build backend instead of classic make.
#   Ninja better parallelizes dependencies and gives progress output
#   more readable. If you prefer make, simply omit this flag.
cmake -DCMAKE_BUILD_TYPE=PGO \
      -DCMAKE_INSTALL_PREFIX=/usr \
      -G Ninja \
      ..

# Compile with all available kernels.
# Ninja already parallelizes automatically; you don't need -j $(nproc) explicit,
# although you can pass it if you want to adjust the load.
ninja

# Run the test suite with all available cores.
# --output-on-failure shows the full output of any test
# to fail, which makes diagnosis easier.
# Each ctest "test" actually loads a Prolog file that can
# execute hundreds of assertions internally.
ctest -j $(nproc) --output-on-failure

# Generate the package. CPack automatically detects that apt is available
# and produces a .deb. If you want to be explicit:
#   cpack -G DEB → force Debian format
#   cpack -G RPM → force Red Hat format (for Fedora/RHEL)
cpack

# The resulting file will have a name similar to:
#   swipl-10.1.5-1.amd64.deb
# and is located in the current build/ directory.
ls -lh swipl-*.deb

sudo apt purge 'swi-prolog*' && sudo apt autoremove

# Using 'apt install ./file.deb' instead of 'dpkg -i' has an advantage
# Important: APT automatically resolves dependencies that might
# missing, rather than failing with a dpkg error and forcing you to do
# 'apt -f install' below.
# The leading './' is required for apt to interpret the argument
# as a local path and not as a repository package name.
sudo apt install ./swipl-*.deb

cd swipl-devel

# Brings the latest changes from the remote repository.
git pull

# Updates the submodules to the versions referenced by the new HEAD.
git submodule update --init --recursive

# Go back to the build directory and reconfigure if necessary.
cd build
cmake ..
ninja
cpack

# Install the new .deb over the old one. APT manages it as a
# normal update (replaces previous package).
sudo apt install ./swipl-*.deb

# Since the .deb was installed via APT, it is uninstalled the same as any other
# another package. The package name generated by CPack is "swipl".
sudo apt purge swipl
sudo apt autoremove

# curl - will download the GPG key from the Ubuntu keyserver.
# gnupg: will process (dearmore) the key from ASCII format to binary.
# ca-certificates: Root certificates for curl to validate HTTPS.
sudo apt update
sudo apt install -y curl gnupg ca-certificates

# Create the keyrings directory if it does not exist.
# -d → create the directory (and any necessary parents).
# -m 0755 → permissions: readable and executable by everyone, writable only by root.
sudo install -d -m 0755 /etc/apt/keyrings

# Download the PPA public key from the Ubuntu keyserver and
# converts from ASCII-armored format (the one issued by keyservers) to
# binary format that apt expects in /etc/apt/keyrings/.
#
# curl -fsSL:
#   -f → fails silently if the server returns an HTTP error.
#   -s → silent mode (does not show progress).
#   -S → does show errors even if -s is active.
#   -L → follows HTTP redirects.
#
# gpg --dearmor:
#   Converts the PEM/ASCII key to OpenPGP binary format.
#
# -o /etc/apt/keyrings/swi-prolog.gpg:
#   Write directly to the final destination with sudo.
curl -fsSL \
  "https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x73E75048FF27533C0D8DC521EF8406856DBFCA18" \
  | sudo gpg --dearmor -o /etc/apt/keyrings/swi-prolog.gpg

# Set permissions: readable by all (apt reads it as root but
# It is good practice to leave it legible).
sudo chmod 0644 /etc/apt/keyrings/swi-prolog.gpg

# Lists the keys of the newly created keyring.
# You should see the fingerprint 73E7 5048 FF27 533C… and the uid
# "Launchpad PPA for SWI Prolog".
gpg --no-default-keyring \
    --keyring /etc/apt/keyrings/swi-prolog.gpg \
    --list-keys

# Create the font file. Here tee is used to write with sudo.
# The heredoc (<<EOF … EOF) passes the multi-line content as stdin.
sudo tee /etc/apt/sources.list.d/swi-prolog.sources > /dev/null <<EOF
# Repository: SWI-Prolog Stable PPA
# Source: https://launchpad.net/~swi-prolog/+archive/ubuntu/stable
# DEB822 format documentation: man sources.list

# Types: deb → binary packages. Add "deb-src" if you want the sources.
Types: deb

# URIs: the base URL of the PPA. Note that it is /stable/ubuntu, not /trixie.
# For the development branch, change "stable" to "devel".
URIs: https://ppa.launchpadcontent.net/swi-prolog/stable/ubuntu

# Suites: the Ubuntu codename with glibc compatible with Debian 13 Trixie.
# DO NOT write "trixie" here: that codename does not exist in the PPA.
Suites: noble

# Components: "main" is the standard PPA component.
# Add "main/debug" if you also want the -dbgsym packages.
Components: main

# Architectures: Limit downloading of indexes to your architecture.
# Prevent apt from trying to download lists for i386, arm64, etc. needlessly.
# Change it to "arm64" if you are on a Raspberry Pi 4/5 or similar.
Architectures: amd64

# Signed-By: Link THIS source to THIS key. The key is only valid
# for this repository and is not converted to a global trust key.
# This is the correct security mechanism in Debian 12+.
Signed-By: /etc/apt/keyrings/swi-prolog.gpg
EOF

# Downloads the indexes of all configured repositories, including
# the newly added PPA. You should see a line like:
#   Get:N https://ppa.launchpadcontent.net/swi-prolog/stable/ubuntu titled InRelease
# If you see a 404 or "does not have a Release file", check the Suites: value.
sudo apt update

# Install SWI-Prolog from the PPA. APT will automatically select the
# highest version available between the PPA and the Debian repositories.
# Since the PPA has 10.x and Debian has 9.2.9, the PPA will win.
sudo apt install swi-prolog

sudo tee /etc/apt/preferences.d/swi-prolog.pref > /dev/null <<EOF
# Sets preference for the SWI-Prolog PPA over any other source.
#
# Package: The 'swi-prolog*' pattern covers the metapackage and all
# sub-packages: swi-prolog-core, swi-prolog-nox, swi-prolog-x, etc.
Package: swi-prolog*

# Pin: Identifies the source by hostname. launchpadcontent.net is the
# domain of all PPAs hosted on Launchpad.
Pin: origin "ppa.launchpadcontent.net"

# Pin-Priority: 1001
#   > 1000 → this package is preferred even over newer versions
#             in other repositories, and allows you to downgrade the PPA
#             if necessary.
#   Without this file, the default priority is 500.
Pin-Priority: 1001
EOF

# Shows where the installation candidate is coming from and with what priority.
# The PPA line must appear first with priority 1001.
apt-cache policy swi-prolog

swipl --version

# Edit the source file and add "main/debug" to Components.
sudo nano /etc/apt/sources.list.d/swi-prolog.sources
# Change the line:
#   Components: main
# by:
#   Components: main main/debug

sudo apt update

# Install kernel debug symbols.
# -dbgsym packages are available for all sub-packages.
sudo apt install swi-prolog-nox-dbgsym

# Edit the source file and change "stable" to "devel" in URIs.
sudo nano /etc/apt/sources.list.d/swi-prolog.sources

sudo apt update

# Reinstall to get the development version.
sudo apt install --reinstall swi-prolog

# Remove SWI-Prolog and its configuration files.
sudo apt purge 'swi-prolog*'
sudo apt autoremove

# Delete the PPA source file.
sudo rm /etc/apt/sources.list.d/swi-prolog.sources

# Remove the GPG key from the PPA.
sudo rm /etc/apt/keyrings/swi-prolog.gpg

# Delete the pinning file (if you created it).
sudo rm -f /etc/apt/preferences.d/swi-prolog.pref

# Updates the indexes to reflect the removal of the PPA.
sudo apt update