How to check if a kernel watchdog is active in Linux

Introduction

In this lab, you will learn how to check if a kernel watchdog is active in Linux. We will explore different methods to determine the status of the watchdog timer, a critical component for ensuring system stability by automatically rebooting unresponsive systems.

You will begin by checking the watchdog status using the /proc filesystem, then verify its initialization in the kernel message buffer with dmesg, and finally inspect the watchdog service configuration in /etc/systemd. These steps will provide a comprehensive understanding of how to ascertain the operational state of the Linux kernel watchdog.

Skills Graph

%%%%{init: {'theme':'neutral'}}%%%% flowchart RL linux(("Linux")) -.-> linux/BasicFileOperationsGroup(["Basic File Operations"]) linux(("Linux")) -.-> linux/TextProcessingGroup(["Text Processing"]) linux/BasicFileOperationsGroup -.-> linux/ls("Content Listing") linux/BasicFileOperationsGroup -.-> linux/cat("File Concatenating") linux/TextProcessingGroup -.-> linux/grep("Pattern Searching") subgraph Lab Skills linux/ls -.-> lab-558727{{"How to check if a kernel watchdog is active in Linux"}} linux/cat -.-> lab-558727{{"How to check if a kernel watchdog is active in Linux"}} linux/grep -.-> lab-558727{{"How to check if a kernel watchdog is active in Linux"}} end

Check watchdog status with cat /proc/sys/kernel/watchdog

In this step, we will explore the Linux watchdog timer. The watchdog is a system that can automatically reboot the computer if it becomes unresponsive. This is crucial for critical systems where downtime is unacceptable.

The watchdog timer is controlled by a kernel parameter. We can check its status by reading a special file in the /proc filesystem. The /proc filesystem is a virtual filesystem that provides information about processes and other system information.

We will use the cat command to read the content of the file that controls the watchdog status.

Type the following command in your terminal and press Enter:

cat /proc/sys/kernel/watchdog

The output of this command will be either 0 or 1.

0: Indicates that the watchdog timer is disabled.
1: Indicates that the watchdog timer is enabled.

You should see an output similar to this:

This means the watchdog timer is currently disabled in this environment. Understanding the status of the watchdog is the first step in managing it.

Click Continue to proceed to the next step.

Verify watchdog in dmesg

In this step, we will examine the kernel message buffer using the dmesg command. dmesg displays messages from the kernel, which are generated during system startup and operation. These messages often contain information about hardware detection, driver loading, and system events, including the initialization of the watchdog timer.

We will use dmesg and pipe its output to grep to filter for messages related to the watchdog. Piping (|) sends the output of one command as the input to another command.

Type the following command in your terminal and press Enter:

dmesg | grep -i watchdog

Let's break down this command:

dmesg: Displays the kernel message buffer.
|: The pipe operator, sending the output of dmesg to grep.
grep: A powerful command-line utility for searching plain-text data sets for lines that match a regular expression.
-i: An option for grep that ignores case distinctions in the pattern.
watchdog: The pattern we are searching for in the kernel messages.

The output will show any kernel messages that contain the word "watchdog", regardless of case. If the watchdog driver was loaded or initialized during boot, you might see output similar to this (the exact output may vary depending on the system):

[    0.XXX] Linux version X.X.X-XX-generic (...)
[    X.XXX] watchdog: initialized omap_wdt driver
[    X.XXX] watchdog: watchdog0: watchdog: activate

If you see output like this, it indicates that the kernel detected and initialized a watchdog device. If you see no output, it might mean the watchdog driver was not loaded or is not present on this system.

This command is useful for verifying if the kernel is aware of and interacting with a watchdog device.

Click Continue to move on.

Inspect watchdog service in /etc/systemd

In this step, we will look for configuration files related to the watchdog service within the /etc/systemd directory. systemd is a system and service manager for Linux, and it often manages services like the watchdog. Configuration files for systemd units (like services) are typically stored in /etc/systemd/system/.

We will use the ls command to list files and then grep to search for files containing "watchdog" in their name within the /etc/systemd/system/ directory.

Type the following command in your terminal and press Enter:

ls /etc/systemd/system/ | grep watchdog

Let's break down this command:

ls /etc/systemd/system/: Lists the contents of the /etc/systemd/system/ directory.
|: The pipe operator, sending the output of ls to grep.
grep watchdog: Searches for lines containing the word "watchdog".

If a watchdog service is configured using systemd, you might see output similar to this:

watchdog.service

This indicates that a systemd service file named watchdog.service exists, which is likely responsible for managing the watchdog timer. The presence of this file suggests that the watchdog functionality might be controlled and configured through systemd.

If you see no output, it means there is no systemd service file explicitly named with "watchdog" in this directory. This doesn't necessarily mean the watchdog isn't active, but it suggests it's not being managed by a standard systemd watchdog service unit file in this location.

Understanding where watchdog services are configured is important for managing their behavior.

Click Continue to finish this lab.

Summary

In this lab, we learned how to check the status of the kernel watchdog in Linux. We began by using the cat /proc/sys/kernel/watchdog command to determine if the watchdog timer is enabled or disabled, observing that a value of 0 indicates disabled and 1 indicates enabled.

Following this, we explored the kernel message buffer using dmesg and piped the output to grep -i watchdog to search for messages related to the watchdog timer, which can provide insights into its initialization and status during system startup.