Complete Guide to Forcing Shutdown When Ubuntu Freezes | How to Close Unresponsive Apps and Prevent Freezes

By 佐川 直弘 | Naohiro Sagawa (運営者)

※記事内に広告を含みます。Amazonアソシエイトとして適格販売により収入を得ています。　

1. Introduction

It’s not uncommon for the system or applications to freeze suddenly while using Ubuntu. This is especially likely when multiple applications are open simultaneously or when running tasks that consume a large amount of system resources.

When a freeze occurs, the mouse and keyboard may become unresponsive, preventing you from continuing your work. In such situations, it is crucial to resolve the issue properly. Performing the wrong actions may lead to data loss or system instability, so careful handling is required.

This article will briefly explain the causes of freezes in Ubuntu and provide detailed instructions on how to force quit applications safely while minimizing risks. Additionally, we will cover methods to force restart the entire system and offer tips on preventing freezes from occurring.

By reading this article, you will learn:

• How to safely close unresponsive applications
• How to restart the entire system
• Tips to prevent future freezes

This knowledge is useful not only for beginners but also for intermediate users and Ubuntu administrators. If you want to reduce the frequency of freezes and minimize disruptions during work, the information provided here will be invaluable. By following this guide, you can develop the skills needed to use Ubuntu more smoothly.

In the next section, we will discuss the risks and precautions associated with force quitting applications.

2. Risks and Precautions of Force Quitting

Forcing an unresponsive application or system to close can be a very useful solution when work is interrupted. However, force quitting comes with risks, so it should be done carefully. This section explains the potential impacts of force quitting and how to minimize those risks.

Potential Risks of Force Quitting

1. Data Loss

When force quitting an application, any unsaved data may be lost. For example, if a freeze occurs while working on a document and you force quit the application, all unsaved work will be lost.

2. System Instability

If a critical system process is forcibly terminated, the entire Ubuntu system may become unstable. In the worst-case scenario, errors may occur after restarting, preventing the system from functioning properly.

3. File System Damage

Force quitting may interrupt ongoing file or disk write operations. This can lead to file system corruption, making data recovery difficult.

Precautions for Safe Force Quitting

1. Wait for a Response Before Force Quitting

Even if the system appears frozen, waiting for a few minutes may allow it to recover. This is especially true for applications that consume a lot of resources, as they might resume normal operation after some time. Before force quitting, consider waiting to see if the application responds.

2. Identify Critical Processes

Before force quitting, check whether the process you are about to terminate affects essential system functions. You can use the System Monitor or the ps command in the terminal to view running processes.

3. Attempt to Save Data

Even in a frozen state, you may still be able to manually save your data. If possible, try saving your work before the application becomes completely unresponsive.

4. Regularly Back Up Your Data

To prepare for unexpected data loss, make it a habit to back up your Ubuntu environment regularly. You can use tools like Deja Dup to create backups easily.

3. How to Close Unresponsive Applications

When an application becomes unresponsive in Ubuntu, it is important to close it using an appropriate method. This section provides a detailed explanation of two approaches: using the graphical user interface (GUI) and using command-line tools. You can choose the method that best suits your skill level and needs.

Using the System Monitor

Step 1: Open the System Monitor

• Search for “System Monitor” in the menu and open it.
  Alternatively, you can press Ctrl + Alt + Del to access it.

Step 2: Identify the Unresponsive Process

• The System Monitor displays a list of currently running processes.
  Check the process name and CPU usage to locate the frozen application.

Step 3: End the Process

• Select the unresponsive application and click the “End Process” or “Kill Process” button.
  Note: Force quitting may result in unsaved data loss, so proceed with caution.

Using the Command Line

The command line provides a more direct and powerful way to control processes. Below are some commonly used commands.

Step 1: Check the Process ID (PID)

• Open a terminal and enter the following command to list running processes:

  ps aux

• To filter a specific application, use:

  ps aux | grep application_name

Example: ps aux | grep firefox

Step 2: Use the Kill Command

• Once you find the process ID (PID), use the following command to terminate it:

  kill PID

Example: kill 12345

Step 3: Force Termination if Needed

• If the standard kill command does not work, use the following force kill command with the -9 option:

  kill -9 PID

Using pkill and killall Commands

pkill and killall allow you to terminate processes using their names.

Using pkill

• To kill a process by name:

  pkill process_name

Example: pkill firefox

Using killall

• To terminate all processes with the same name:

  killall process_name

Example: killall firefox

Precautions

• Before force quitting, ensure that the process is not essential for system stability.
• To prevent data loss, consider waiting before terminating an unresponsive application.

4. How to Force Restart the Entire System

In some cases, not just an individual application but the entire Ubuntu system may become unresponsive. When this happens, you need to restart the system. This section explains two methods: using a virtual console and using the Magic SysRq key.

Using a Virtual Console

A virtual console allows you to restart the system via the command line, even if the graphical user interface (GUI) is unresponsive.

Step 1: Switch to a Virtual Console

• Press Ctrl + Alt + F2 to switch to a virtual console.
• You can also use Ctrl + Alt + F3 to F6 to access other virtual consoles.

Step 2: Log In

• Enter your username and password to log in to the virtual console.

Step 3: Execute the Restart Command

• Enter the following command to restart the system:

  sudo reboot

• If prompted, enter your password (the same one used for login).

Precautions

• If you are unable to switch to a virtual console, try using the Magic SysRq key method described below.

Using the Magic SysRq Key

The Magic SysRq key is a special feature that allows you to safely restart Ubuntu even when the system is completely unresponsive. This method follows a structured approach to prevent data loss.

What is the Magic SysRq Key?

• The Magic SysRq key is a low-level command feature built into the Linux kernel.
• It is used by pressing the Alt key along with the SysRq (Print Screen) key.

Step 1: Press Alt + SysRq and Enter the Following Keys in Order

• Use the following key sequence, known as REISUB, to safely restart the system:

1. R: Switch the keyboard back to raw mode
2. E: Send SIGTERM to all processes
3. I: Send SIGKILL to all processes
4. S: Sync all disk data
5. U: Unmount the file system
6. B: Restart the system

How to Execute the Command

1. Hold down Alt + SysRq.
2. Press each of the above keys (R, E, I, S, U, B) one at a time, in order.

Precautions

• Do not skip any steps in the REISUB sequence. S and U are especially important for preventing data loss.
• Some systems disable the Magic SysRq feature by default. If necessary, enable it in the system settings.

Last Resort: Hard Restart

If none of the above methods work, the last resort is to force a hardware restart by holding down the power button. However, this should only be done as a last measure, as it may result in data loss or file system damage.

Summary

• Using a virtual console allows you to restart the system even if the GUI is unresponsive.
• The Magic SysRq key is a powerful tool for safely restarting a frozen system while minimizing data loss.
• Hard restarts should only be used when all other options fail.

5. Tips to Prevent Freezes

Many freezes in Ubuntu can be prevented. By taking appropriate precautions, you can improve system stability and reduce the frequency of freezes. This section provides practical tips and best practices for avoiding system freezes.

Keep Your System Up to Date

1. Regularly Update Software

• Bugs and compatibility issues are common causes of system freezes. Applying the latest updates helps resolve these problems.
• Use the following commands to keep your system up to date:

  sudo apt update
  sudo apt upgrade

2. Use the Latest Kernel

• Updating the kernel improves hardware compatibility and enhances performance.
• To check your current kernel version, use:

  uname -r

Disable Unnecessary Services and Processes

1. Remove Unnecessary Startup Services

• Unnecessary services and applications running at startup consume system resources and may cause freezes.
• You can manage startup processes using the Startup Applications tool.

2. Stop Unnecessary Applications

• Stopping unnecessary running processes in real-time can save system resources.
• Use the htop command to monitor and manage processes:

  sudo apt install htop
  htop

Monitor Hardware Resources

1. Check Disk Space Regularly

• Running out of disk space can cause the system to freeze, especially in the /var and /home directories.
• Check disk usage with:

  df -h

2. Monitor Memory Usage

• Insufficient memory can also cause freezes. Check memory usage with:

  free -h

• If needed, consider increasing swap space.

Summary

• Keeping your system updated, disabling unnecessary processes, and monitoring hardware resources can help prevent freezes.
• Implementing small preventive measures contributes to a more stable and efficient Ubuntu environment.

6. Conclusion

System freezes in Ubuntu can be frustrating, especially when they disrupt important work. However, by following the right troubleshooting steps and taking preventive measures, you can significantly reduce the occurrence of freezes and maintain a stable system.

Key Takeaways

• How to force quit unresponsive applications: Using System Monitor and command-line tools like kill and pkill.
• How to force restart the system: Using a virtual console or the Magic SysRq key for safe reboots.
• How to prevent freezes: Regularly updating software, disabling unnecessary processes, and monitoring system resources.

By applying these techniques, you can ensure a more stable and efficient Ubuntu experience. Keep this guide handy, share it with other Ubuntu users, and make proactive system maintenance a habit!