A tiny example: Execute "notify-send" from container to send messages to host

notify_send_docker.sh

#!/usr/bin/env bash

# ref: https://forums.docker.com/t/communicate-with-dbus-from-an-unprivileged-container/101549
# ref: https://stackoverflow.com/questions/23601844/how-to-create-user-in-linux-by-providing-uid-and-gid-options
# ref: https://github.com/mviereck/x11docker/wiki/How-to-connect-container-to-DBus-from-host

set -euxo pipefail

readonly DBUS_USER_SESSION_PATH="${DBUS_SESSION_BUS_ADDRESS#"unix:path="}"

readonly uid=$(id -u)
readonly gid=$(id -g)

docker run -it \
  --rm \
  --privileged \
  --security-opt "apparmor:unconfined" \
  --cap-add ALL \
  -v /var/run/dbus:/var/run/dbus \
  -e DBUS_SESSION_BUS_ADDRESS="$DBUS_SESSION_BUS_ADDRESS" \
  -v "${DBUS_USER_SESSION_PATH}:${DBUS_USER_SESSION_PATH}" \
  ubuntu:22.04 \
  /bin/bash -c "apt update && apt install -y libnotify-bin && groupadd -g ${gid} user && useradd user -u ${uid} -g ${gid} -m -s /bin/bash && su user -s /bin/bash -c '/usr/bin/notify-send test-1'"