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Linux: systemd target units examples

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Here is a list of some systemd target units along with examples of how to use them:

  1. multi-user.target:
    • This target is used for a multi-user system without a graphical interface. It includes services required for a text-based or command-line environment.
    • Example: To switch to the multi-user target, you can use the following command: sudo systemctl isolate multi-user.target
  2. graphical.target:
    • Represents a multi-user system with a graphical interface (GUI). It includes services required for a graphical desktop environment.
    • Example: To switch to the graphical target, you can use the following command:sudo systemctl isolate graphical.target
  3. rescue.target:
    • Similar to runlevel 1 or single-user mode in traditional SysVinit systems. It provides a minimal environment with a root shell for system recovery and maintenance tasks.
    • Example: To switch to the rescue target, you can use the following command:sudo systemctl isolate rescue.target
  4. emergency.target:
    • Provides the most minimal environment possible, intended for emergencies where the system is in an unusable state. It drops the system into a single-user shell without starting any services.
    • Example: To switch to the emergency target, you can use the following command:sudo systemctl emergency
  5. shutdown.target:
    • Used to gracefully shut down the system. All services are stopped, and the system is powered off or rebooted, depending on the shutdown command used.
    • Example: To initiate a shutdown using this target, you can use the following command:sudo systemctl shutdown
  6. network.target:
    • Represents the availability of the network. Other services that depend on network connectivity may be started after this target is reached.
    • Example: To view the status of the network target, you can use the following command:systemctl status network.target
  7. sockets.target:
    • Represents the availability of system sockets. Services that provide network services via sockets may be started after this target is reached.
    • Example: To view the status of the sockets target, you can use the following command:systemctl status sockets.target

These are some of the systemd target units along with examples of how to use them. Depending on your specific distribution and configuration, there may be additional targets or custom targets defined. You can explore more targets and their usage by referring to the systemd documentation or using the systemctl list-units --type=target command.

Linux: Systemd target units

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Systemd target units are used to group and manage services and other units in Linux distributions that use systemd as the init system. Targets are similar to runlevels in traditional SysVinit systems but offer more flexibility and granularity in defining system states and dependencies between units.

Here are some common systemd target units:

  1. default.target:
    • This is the default target unit that the system boots into. It typically represents the normal operational state of the system.
  2. multi-user.target:
    • Represents a multi-user system without a graphical interface. It includes services required for a text-based or command-line environment.
  3. graphical.target:
    • Represents a multi-user system with a graphical interface (GUI). It includes services required for a graphical desktop environment.
  4. rescue.target:
    • Similar to runlevel 1 or single-user mode in traditional SysVinit systems. It provides a minimal environment with a root shell for system recovery and maintenance tasks.
  5. emergency.target:
    • Provides the most minimal environment possible, intended for emergencies where the system is in an unusable state. It drops the system into a single-user shell without starting any services.
  6. shutdown.target:
    • Used to gracefully shut down the system. All services are stopped, and the system is powered off or rebooted, depending on the shutdown command used.
  7. poweroff.target:
    • Initiates a system poweroff, shutting down the system and powering off the hardware.
  8. reboot.target:
    • Initiates a system reboot, shutting down the system and restarting the hardware.
  9. network.target:
    • Represents the network being available. Other services that depend on network connectivity may be started after this target is reached.
  10. basic.target:
    • A minimal target that is reached early during the boot process. It includes basic system initialization and dependency handling.
  11. sockets.target:
    • Represents the availability of system sockets. Services that provide network services via sockets may be started after this target is reached.
  12. timers.target:
    • Represents the availability of system timers. Services that depend on timers for scheduling tasks may be started after this target is reached.

These are some of the common systemd target units used in Linux distributions. Depending on the specific distribution and configuration, there may be additional targets or custom targets defined. You can view the available targets on your system using the systemctl list-units --type=target command.

Python Flask programming reference sites

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  1. Official Flask Documentation:
    • Flask Documentation
      • The official documentation provides comprehensive information about Flask, including installation, quickstart guide, and detailed explanations of Flask features and concepts.
  2. Flask GitHub Repository:
    • Flask GitHub Repository
      • The Flask source code is available on GitHub. You can explore the repository to understand the implementation details and contribute to the Flask project.
  3. Flask Quickstart Guide:
    • Flask Quickstart
      • The quickstart guide is a great starting point for beginners. It covers the basic steps to create a simple Flask application.
  4. Flask Mega-Tutorial by Miguel Grinberg:
    • Flask Mega-Tutorial
      • This tutorial by Miguel Grinberg is a comprehensive guide to building a full-featured web application with Flask. It covers a wide range of topics and is suitable for both beginners and intermediate learners.
  5. Real Python Flask Tutorials:
    • Real Python Flask Tutorials
      • Real Python offers a variety of tutorials covering Flask, from basic concepts to more advanced topics. The tutorials include video content and written guides.
  6. Flask Web Development Book by Miguel Grinberg:
    • Flask Web Development Book
      • Miguel Grinberg’s book “Flask Web Development” provides in-depth coverage of Flask, including building web applications, handling databases, and more.
  7. Flask by Example Series on PyBites:
    • Flask by Example
      • PyBites offers a Flask by Example series, which guides you through building Flask applications step by step.
  8. Awesome Flask:
    • Awesome Flask
      • The Awesome Flask GitHub repository is a curated list of Flask resources, including extensions, tutorials, and tools.
  9. Flask WTF Documentation (WTForms):
    • Flask WTF Documentation
      • If you are working with web forms in Flask, the Flask WTF (WTForms) documentation is a valuable resource.
  10. Explore Flask:
    • Explore Flask
      • Explore Flask is a free online book that covers Flask concepts and provides practical examples.

Remember to check the official Flask documentation for the most up-to-date and accurate information. Additionally, exploring community forums, such as the Flask community on Stack Overflow, can be helpful for getting answers to specific questions.