lightdm

lightdm [OPTIONS]
Note: lightdm is typically started by the system's init system (e.g., systemd) as a daemon, rather than being invoked manually by users with command-line options for daily operation. The options below are primarily for debugging or specifying alternative configuration.

-h, --help
    Displays a help message and exits.

-c FILE, --config=FILE
    Specifies an alternative configuration file to use instead of the default.

-s FILE, --session-config=FILE
    Specifies an alternative session configuration file.

-l FILE, --log-file=FILE
    Directs logging output to the specified file.

-r DIR, --run-dir=DIR
    Sets the directory where LightDM stores runtime files like sockets and PIDs.

-D, --debug
    Enables verbose debugging output, useful for troubleshooting.

--test-mode
    Runs LightDM in a test mode, often used for development or configuration validation without affecting the main system.

lightdm is a versatile and lightweight
display manager for Linux and other Unix-like operating systems. It provides a graphical login interface, allowing users to select their desired session and securely log in to their desktop environment. Developed with performance and cross-desktop compatibility in mind, it is often favored for environments like XFCE, LXDE, and MATE. Unlike heavier display managers, lightdm focuses on a modular design, separating the core display management logic from the user-facing login screen, known as the "greeter." This architecture allows for various greeters (e.g., GTK+, Qt-based) to be plugged in, offering extensive customization options for the visual appearance and functionality of the login screen. It effectively handles X server management, session startup, and user authentication, ensuring a smooth transition from boot to desktop.

lightdm is usually managed by the system's init system (like systemd) and not intended for direct manual execution by users for daily use.
Its primary configuration is done through files in /etc/lightdm/, especially lightdm.conf.
A functional greeter (e.g., lightdm-gtk-greeter) must be installed and configured for the graphical login screen to appear.

The core behavior and appearance of lightdm are extensively customized via configuration files, primarily /etc/lightdm/lightdm.conf and files within /etc/lightdm/lightdm.conf.d/. These files control greeter settings, session default, user lists, autologin, and more.

lightdm employs a modular design where the actual graphical login screen is provided by a separate component called a "greeter." Common greeters include lightdm-gtk-greeter (GTK+ based) and lightdm-kde-greeter (Qt based), which can be installed and configured independently to match the desktop environment's aesthetic.

lightdm was initially developed by Canonical Ltd. for Ubuntu, making its debut in Ubuntu 11.10 "Oneiric Ocelot" in October 2011. It was designed to be a faster, more lightweight, and highly customizable alternative to the then-default GNOME Display Manager (GDM). Although Ubuntu has since transitioned back to GDM for better integration with GNOME Shell, lightdm remains a popular choice for other distributions and desktop environments, particularly those focused on performance and customizability like XFCE, LXDE, and MATE.

gdm(1), sddm(1), xdm(1), lightdm.conf(5), display-manager(7)