View Kernel Messages in Linux | dmesg Command (original) (raw)

Last Updated : 15 Nov, 2025

The dmesg (display message) command is used to view kernel messages from the ring buffer, providing insights into hardware detection, driver initialization, and system errors during boot and runtime.

• Displays low-level kernel and hardware messages not visible in standard logs.
• Useful for diagnosing hardware failures, driver issues, and boot problems.
• The kernel messages are stored temporarily in the ring buffer and permanently in /var/log/dmesg.
• Supports options like -T for readable timestamps and --follow to monitor live kernel events in real time.

Basic Example: View All Kernel Messages

This displays all messages from the kernel ring buffer.

**Command:

sudo dmesg

**Output:

Key Options of dmesg command

The following are the options of dmesg command with describing its functionality:

Syntax of the dmesg Command

dmesg [options]

Installation and setup dmesg command

The following are the steps that guides in install and setup the dmesg command:

**Step 1: Check if dmesg is Installed

Firstly, whether the dmesg software is already available or not using the following command:

which dmesg

**Step 2: Install dmesg

For Debian-based systems (Ubuntu, Mint, etc.):

sudo apt udpate
sudo apt install util-linux

For RedHat-based systems (Fedora, CentOS, etc.):

sudo yum install util-linux

**Step 3: Verify dmesg Installation

After installation of **dmesg command, verify its successful installation using the following command:

dmesg --version

Basic Usage and Examples of dmesg Command

The dmesg command provides detailed kernel-level information useful for diagnosing hardware, driver, and boot-related issues. Below are common examples demonstrating its basic usage and key functionalities.

1. Viewing Logs Page-Wise with Less

• Used to scroll through kernel messages conveniently, one page at a time.

**Command:

sudo dmesg | less

**Output:

Here,

• Displays kernel messages page by page for easier reading.
• The less pager allows smooth scrolling through long outputs.
• Prevents terminal overflow and improves readability.

2. Colorizing dmesg Output

• Adds color to different log types for better visibility and quick identification.

**Command:

sudo dmesg -L

**Output:

Here,

• Highlights errors, warnings, and informational messages in different colors.
• Makes log analysis faster and visually easier.
• Ideal for distinguishing critical events at a glance.

3. Displaying Human-Friendly Timestamps

• Converts raw timestamps into seconds and nanoseconds for easier reading.

**Command:

sudo dmesg -H

**Output:

Here,

• Displays timestamps in an easily readable format.
• Shows precise timing of kernel messages since boot.
• Helps track system events with microsecond accuracy.

**4. Displaying Standard Date and Time Format

• Shows log timestamps in a standard, human-readable date and time format.

**Command:

sudo dmesg -T

**Output:

Here,

• Converts timestamps into real-world date and time.
• Useful for correlating kernel messages with system or user actions.
• Slightly reduces time resolution to improve readability.

**5. Monitoring Real-Time Logs

• Continuously displays new kernel messages as they are generated.

**Command:

sudo dmesg --follow

**Output:

**Explanation:

• Works like tail-f for live kernel log updates.
• Shows new events such as hardware connections or system errors in real time.
• Useful for monitoring system behavior continuously.

**6. Viewing Specific Number of Messages with Head

• Displays only the first few kernel messages for a concise overview.

**Command:

sudo dmesg | head -10

**Output:

**Explanation:

• Shows the first 10 messages from the kernel log.
• Useful for reviewing early boot or initialization events.
• Helps focus on startup information only.

**7. Viewing Last 10 Messages with Tail

• Shows the most recent kernel messages for quick inspection.

**Command:

sudo dmesg | tail -10

**Output:

**Explanation:

• Displays the last 10 kernel log entries.
• Helps identify recent hardware or system changes.
• Commonly used for troubleshooting after connecting devices.

8. Case-Insensitive Searching

Finds specific messages without worrying about uppercase or lowercase text.

**Command:

sudo dmesg | grep -i usb

**Output:

**Explanation:

• Searches for messages containing “USB” or “usb”.
• Helps verify whether USB devices were detected correctly.
• Simplifies pattern-based message filtering.
• Searches kernel messages related to disks or storage devices.

**Command:

sudo dmesg | grep -i sda

**Output:

**Explanation:

• Finds log entries related to disk drives (/dev/sda).
• Displays events like detection, mounting, or disk errors.
• Commonly used to troubleshoot hard drive or SSD issues.

10. Filtering Messages by Log Level (Info)

• Displays kernel messages based on their severity or importance level.

**Command:

sudo dmesg -l info

**Output:

**Explanation:

• Shows informational messages only.
• Filters logs to focus on normal system operations.
• Reduces noise from warnings or errors for clarity.

11. Combining Multiple Log Levels

• Retrieves kernel messages that match more than one log level.

**Command:

sudo dmesg -l debug,notice

**Output:

**Explanation:

• Displays both debug and notice-level messages.
• Helps developers track both normal and detailed system activities.
• Useful for performance monitoring and testing.

12. Combining Log Levels (err and warn)

Filters messages to show only errors and warnings for quick issue detection.

**Command:

sudo dmesg --level=err,warn

**Output:

**Explanation:

• Shows critical system issues and warnings together.
• Simplifies troubleshooting by focusing on potential problems.
• Useful for detecting driver or kernel module errors.

**13. Filtering Messages for Specific Network Interface (eth0)

• Displays messages related to a particular network interface, like eth0.

**Command:

sudo dmesg | grep -i eth0

**Output:

**Explanation:

• Filters logs for a specific network adapter.
• Shows driver loading, link status, and connection issues.
• Helps in diagnosing network-related problems.

14. Filtering Messages by Facility (daemon)

• Shows kernel messages categorized under a specific facility.

**Command:

sudo dmesg -f daemon

**Output:

**Explanation:

• Filters logs by facility (e.g., daemon, kernel, system).
• Helps target messages from a particular source or subsystem.
• Useful for narrowing log analysis to specific components.

15. Decoding Facility and Level

Displays each log message with readable facility and severity labels.

**Command:

sudo dmesg -x

**Output:

**Explanation:

• Adds facility and log level prefixes to each message.
• Makes it easier to identify where messages come from and their severity.
• Ideal for advanced log analysis and debugging.

Difference between syslog and dmesg

The following are the difference between syslog and dmesg: