Only figured this out yesterday:
pinentry, which is used to safely enter a password on Linux, has several frontends. There’s a GTK one, a Qt one, even an ncurses one, and so on.
GnuPG also uses pinentry. And you can configure your frontend of choice here in gpg-agent.conf.
But what happens when you don’t configure it? What’s the default?
Turns out, pinentry is a shellscript wrapper and it’s not even that long. Here it is in full:
#!/bin/bash
# Run user-defined and site-defined pre-exec hooks.
[[ -r "${XDG_CONFIG_HOME:-$HOME/.config}"/pinentry/preexec ]] && \
. "${XDG_CONFIG_HOME:-$HOME/.config}"/pinentry/preexec
[[ -r /etc/pinentry/preexec ]] && . /etc/pinentry/preexec
# Guess preferred backend based on environment.
backends=(curses tty)
if [[ -n "$DISPLAY" || -n "$WAYLAND_DISPLAY" ]]; then
case "$XDG_CURRENT_DESKTOP" in
KDE|LXQT|LXQt)
backends=(qt qt5 gnome3 gtk curses tty)
;;
*)
backends=(gnome3 gtk qt qt5 curses tty)
;;
esac
fi
for backend in "${backends[@]}"
do
lddout=$(ldd "/usr/bin/pinentry-$backend" 2>/dev/null) || continue