LightDM Design

什么是DM？

DM（显示管理器）功能如下：

• 启动和管理本地实例化的X Server；
• 用户认证；
• 启动和管理用户回话（常用情景）；
• 在boot过程中，单例启动X 服务器和开始一个用户会话（(kiosk mode)）；
• 在boot过程中，单例启动 X服务器，显示用户登录界面，在连接时启动用户会话；
• 支持多用户同时登录，用户选择具体用户登录，同时为每一个 用户启动 X 服务器；
• 允许 X 服务器，使用XDMCP，运行瘦客户端远程连接到其他X 服务器。

设计目标

• 快速

  不增加其他额外的启动时间；

• 异常安全

  处理所有

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

Daemon:

• Implemented in C+GObject
• Single process Greeter Interface:
• D-Bus GTK+ Greeter:

Inter-process Relationships