Lightdm

命令行工具，它可用来锁定当前 seat, 切换会话，等等

$ dm-tool –help

$ sudo apt install xserver-xephyr

$ lightdm –test-mode –debug

默认打开小键盘:

安装 numlockx, 编辑 /etc/lightdm/lightdm.conf 添加以下几行:

[Seat:*]

greeter-setup-script=/usr/bin/numlockx on

$ systemctl status lightdm.service

$ systemctl help lightdm.service

After enabling lightdm a symlink display-manager.service should be set in /etc/systemd/system/. You may need to use –force to override old symlinks.

feng@380:~$ file /etc/systemd/system/display-manager.service

/etc/systemd/system/display-manager.service: symbolic link to /lib/systemd/system/lightdm.service

loginctl –help

Session configuration

Many display managers read available sessions from /usr/share/xsessions/ directory. It contains standard desktop entry files for each DM/WM.

Starting applications without a window manager

You can also launch an application without any decoration, desktop, or window management. For example to launch google-chromeAUR create a web-browser.desktop file in /usr/share/xsessions/ like this:

[Desktop Entry]

Encoding=UTF-8

Name=Web Browser

Comment=Use a web browser as your session

Exec=/usr/bin/google-chrome –auto-launch-at-startup

TryExec=/usr/bin/google-chrome –auto-launch-at-startup

Icon=google-chrome

~/.xinitrc or /etc/X11/xinit/xinitrc

The Light Display Manager (LightDM)

Description

LightDM is a cross-desktop display manager. A display manager is a daemon that:

Runs display servers (e.g. X) where necessary.

Runs greeters to allow users to pick which user account and session type to use.

Allows greeters to perform authentication using PAM.

Runs session processes once authentication is complete.

Provides remote graphical login options.

Key features of LightDM are:

Cross-desktop - supports different desktop technologies.

Supports different display technologies (X, Mir, Wayland …).

Lightweight - low memory usage and fast performance.

Guest sessions.

Supports remote login (incoming - XDMCP, VNC, outgoing - XDMCP, pluggable).

Comprehensive test suite.

Configuration

LightDM configuration is provided by the following files:

/usr/share/lightdm/lightdm.conf.d/.conf_x000D_/etc/lightdm/lightdm.conf.d/.conf_x000D_/etc/lightdm/lightdm.conf

System provided configuration should be stored in /usr/share/lightdm/lightdm.conf.d/. System administrators can override this configuration by adding files to /etc/lightdm/lightdm.conf.d/ and /etc/lightdm/lightdm.conf. Files are read in the above order and combined together to make the LightDM configuration.

配置文件书写规则http://bazaar.launchpad.net/~lightdm-team/lightdm/trunk/view/head:/data/lightdm.conf

LightDM Design

What is a Display Manager?

The responsibilities of a display manager are:

Starting and managing local instances of the X server.

Authenticating users.

Starting and managing user sessions. Common use cases:

Starting a single X server on boot and starting a session (kiosk mode).

Starting a single X server instance on boot, displaying a greeter GUI (username and password), and starting the user session when connected (traditional).

Supporting multiple simultaneous logins by exposing what users are logged in, and starting new X servers for each user (user switching).

Running a thin-client server by allowing X servers to connect using XDMCP, and connecting greeters and sessions to those X servers.

Design Goals

Fast - The display manager should add no noticeable delay to startup time.

Fail-safe - Failures should be handled gracefully.

Secure - Resistant to malicious users.

Flexible - Able to support a range of use-cases.

Extensible - Able to support rarer use-cases though plugins.

Simple - Configuration should be easy and the code should be simple to understand and modify.

Definitions

Display Manager - A daemon that manages the displays on a system.

Display - A combination of an X server, greeter and a user session.

User session - An application that runs on a display and allows the user to run applications.

Greeter - An application to run on a display and prompt for authentication and session options.

Requirements

Daemon:

Able to run as as system service without user interaction

Provide logging information for debugging

Launch and monitor X servers

Launch and monitor greeter applications for displays without a user session

Launch and monitor user sessions after user is authenticated

Authenticate users

Provide an interface to greeter applications

Provide an interface to user switchers

Store a database of active displays

Load sessions from /usr/share/xsessions

Store session configuration in ~/.dmrc

Support .dmrc not being readable before login

Advertise display database to Software/ConsoleKit if available

Use PAM for authentication Session environment:

Set USER to the username

Set HOME to users home directory

Set SHELL to the users shell

Set PATH to /usr/bin:/bin

Set LANG to the users language

Set DISPLAY to the X servers address

Set environment variables from /etc/environment Static Display Module:

Allow 0-N displays to be enabled at all time

Support automatic/timed login User Switcher Module:

Interface to switch to existing local display for a logged in user

Start new static display if user not logged in XDMCP Server Module:

Implement XDMCP protocol Module interface:

Expose display database Greeter application/interface:

User authentication

Session choice

Session language

Session keyboard layout

Logged in users

Implementation