How to use tail command to extract last 20 lines from a log file?

Using the tail Command to Extract the Last 20 Lines from a Log File

As a Linux technical expert and mentor, I'm happy to help you with your question on using the tail command to extract the last 20 lines from a log file.

The tail command is a powerful tool in the Linux command-line interface that allows you to view the last part of a file. It's particularly useful for monitoring log files, where you often want to see the most recent entries to troubleshoot issues or track activity.

Syntax and Options

The basic syntax for using the tail command to extract the last 20 lines from a log file is:

tail -n 20 <log_file>

Here's a breakdown of the command:

• tail: This is the command that you're using to view the last part of the file.
• -n 20: This option specifies that you want to see the last 20 lines of the file. You can adjust the number to suit your needs.
• <log_file>: This is the path to the log file you want to view.

You can also use the -f option to "follow" the log file, which means that the tail command will continuously display new lines as they are added to the file. This is useful for monitoring a log file in real-time. The command would look like this:

tail -f -n 20 <log_file>

Example Usage

Let's say you have a log file named system.log in the /var/log directory. To view the last 20 lines of this file, you would use the following command:

tail -n 20 /var/log/system.log

This will display the last 20 lines of the system.log file in your terminal.

If you want to continuously monitor the log file and see the new entries as they are added, you can use the -f option:

tail -f -n 20 /var/log/system.log

This will keep the tail command running and display the last 20 lines of the log file, updating the output as new lines are added.

Visualizing the Concept

Here's a Mermaid diagram that illustrates the core concept of using the tail command to extract the last 20 lines from a log file:

The diagram shows that the tail command takes the log file as input and extracts the last 20 lines, which are then displayed in the terminal.

Conclusion

The tail command is a simple yet powerful tool for quickly accessing the most recent entries in a log file. By using the -n option, you can specify the number of lines you want to see, and the -f option allows you to continuously monitor the file for new entries.

I hope this explanation has been helpful! Let me know if you have any further questions.