Linux tail Command with Practical Examples

Introduction

In this lab, you will learn how to use the Linux tail command, which is a powerful tool for viewing and monitoring the end of files, particularly log files. The lab covers the purpose and syntax of the tail command, its basic usage for displaying a specific number of lines, following a file, and using it with other commands like grep. This knowledge is valuable for system administrators, developers, and anyone working with text files and logs in a Linux environment.

The lab provides a comprehensive overview of the tail command, including practical examples to help you understand its functionality and apply it effectively in your daily tasks. By the end of this lab, you will be able to efficiently use the tail command to troubleshoot and monitor your system's activity.

Linux Commands Cheat Sheet

Skills Graph

Understand the Purpose and Syntax of the tail Command

In this step, you will learn about the purpose and basic syntax of the tail command in Linux. The tail command is used to display the last few lines of a file or the output of a command.

The basic syntax of the tail command is:

tail [options] [file]

The most common options for the tail command are:

• -n: Specifies the number of lines to display. For example, tail -n 5 file.txt will display the last 5 lines of the file.
• -f: Follows the file, continuously displaying new lines as they are added to the file. This is useful for monitoring log files.

Example usage:

$ tail -n 3 file.txt
This is the third line.
This is the second line.
This is the first line.

Example output:

This is the third line.
This is the second line.
This is the first line.

The tail command is commonly used to view the end of log files, which can be helpful for troubleshooting and monitoring system activity.

Explore the Basic Usage of the tail Command

In this step, you will explore the basic usage of the tail command, including displaying a specific number of lines, following a file, and using the tail command with other commands.

First, let's create a sample text file to work with:

$ echo "Line 1" > sample.txt
$ echo "Line 2" >> sample.txt
$ echo "Line 3" >> sample.txt
$ echo "Line 4" >> sample.txt
$ echo "Line 5" >> sample.txt

Now, let's use the tail command to display the last 3 lines of the file:

$ tail -n 3 sample.txt
Line 3
Line 4
Line 5

Example output:

Line 3
Line 4
Line 5

Next, let's use the -f option to follow the file and see new lines as they are added:

$ tail -f sample.txt
Line 1
Line 2
Line 3
Line 4
Line 5

Press Ctrl+C to stop following the file.

You can also use the tail command with other commands, such as grep to search for specific lines:

$ cat sample.txt | grep "Line 3"
Line 3

Example output:

Line 3

In this way, you can use the tail command to quickly view and monitor the contents of files, especially log files, which can be helpful for troubleshooting and debugging.

Utilize the tail Command for Monitoring Log Files

In this final step, you will learn how to use the tail command to monitor log files, which is one of its most common use cases.

First, let's create a sample log file:

$ touch sample.log
$ echo "2023-04-01 10:00:00 - INFO: Application started" >> sample.log
$ echo "2023-04-01 10:00:15 - DEBUG: Processing request" >> sample.log
$ echo "2023-04-01 10:00:30 - ERROR: Database connection failed" >> sample.log
$ echo "2023-04-01 10:01:00 - INFO: Application shutting down" >> sample.log

Now, let's use the tail command to monitor the log file:

$ tail -f sample.log
2023-04-01 10:00:00 - INFO: Application started
2023-04-01 10:00:15 - DEBUG: Processing request
2023-04-01 10:00:30 - ERROR: Database connection failed
2023-04-01 10:01:00 - INFO: Application shutting down

The -f option tells tail to "follow" the file, which means it will continuously display new lines as they are added to the log file.

You can also use the tail command to search for specific log entries using the grep command:

$ tail -n 10 sample.log | grep "ERROR"
2023-04-01 10:00:30 - ERROR: Database connection failed

This will display the last 10 lines of the log file and filter for any lines containing the word "ERROR".

The tail command is particularly useful for monitoring and troubleshooting live systems, as it allows you to quickly view and search the most recent log entries without having to open the entire log file.

Summary

In this lab, you learned about the purpose and basic syntax of the tail command in Linux, which is used to display the last few lines of a file or the output of a command. You explored the basic usage of the tail command, including displaying a specific number of lines, following a file to continuously display new lines, and using the tail command with other commands like grep to search for specific lines. The tail command is commonly used to view the end of log files, which can be helpful for troubleshooting and monitoring system activity.

Linux Commands Cheat Sheet