Linux Tactic

Logging in Linux: A Complete Guide to Using the Logger Command and Manipulating the Syslog File

Logging in Linux is an essential task that administrators must perform to keep track of system activities. The logger command is a powerful tool that allows users to add custom messages to the syslog file.

In this article, we will explore various ways of using the logger command and learn how to print and manipulate the syslog file.

Syntax of logger command

The logger command is an easy-to-use command-line tool used to generate custom logging messages. To use the logger command, the syntax is as follows:

logger [options] [message]

The message can be any text string or file content that you want to add to the syslog file.

For example, the following command logs a custom message to the syslog file:

logger “This is a custom message.”

Printing syslog file

By default, the syslog file is located at /var/log/syslog. To print the syslog file, you can use the tail command.

The tail command displays the last ten lines of the file. To print the last 20 lines of the syslog file, use the following command:

tail -n 20 /var/log/syslog

This command will display the 20 latest lines of the syslog file.

Specifying syslog lines

The tail command provides an option to specify the exact number of lines you want to display. For example, if you want to display only the first 5 lines of the syslog file, use the command:

tail -n 5 /var/log/syslog

Adding log into syslog file

The logger command can also be used to add custom log messages to the syslog file. For example, if you want to add a custom message to the syslog file, use the following command:

logger “This is a custom message added to the syslog file.”

Logging “who” command

The who command displays a list of all logged-in users.

To log the output of the who command to the syslog file, use the following command:

who | logger

This command pipes the output of the who command to the logger command, which adds the message to the syslog file.

Logging specified file

You can also log the contents of a specified file to the syslog file. To do this, use the -f option with the logger command.

For example, to log the content of a sample file named sample.txt to the syslog file, use the command:

logger -f sample.txt

Specifying log size

You can control the size of the log message using the –size option with the logger command. The –size option indicates the maximum size of the log message that the logger command can accept.

For example, to limit the log message size to 4KB, use the following command:

logger –size 4k “This is a message with a limited size.”

Ignoring empty lines

By default, the logger command adds empty lines to the syslog file. You can prevent the logger command from adding empty lines using the -e option.

For example, to ignore empty lines, use the following command:

logger -e “This is a message without empty lines.”

Displaying help

To display the help message for the logger command, use the –help option. For example, to show the help message, use the following command:

logger –help

Importance of Syslog file

The Syslog file plays a crucial role in keeping track of system activities. The following are the reasons why the syslog file is essential:

Role of syslog file

The syslog file is the central repository for system and application logs. It is responsible for saving all system logs, including kernel messages and application messages.

Saving log data

The syslog file saves all the information about the system activities and log events. It helps to track the history of the system and diagnose problems that may arise in the future.

Accessibility in Linux distributions

The syslog file is accessible in all major Linux distributions. This consistency is essential for users who want to access the logs across various Linux distributions.

Record of each action

The syslog file records each action that occurs on the system. This enables administrators to have a complete overview of the system and detect any anomalies that might occur.

Storing log data in /var/log directory

All log data is stored in the /var/log directory. This arrangement makes it easier for administrators to search and retrieve any log data and to ensure that the log files are not accidentally deleted.

Conclusion

In this article, we have explored various ways of using the logger command to add custom log messages to the syslog file and how to manipulate the syslog file using the tail command. We have also discussed the importance of the syslog file and the role it plays in keeping track of system activities.

By following the methods discussed in this article, you can produce comprehensive log reports that help you troubleshoot system issues and track the system’s performance. In summary, logging in Linux is a crucial aspect of system administration, and the logger command is an essential tool used for generating custom logs.

The syslog file serves as a central repository for all system logs, offers accessibility across Linux distributions, and records every system action. By following the methods discussed in this article, administrators can produce comprehensive log reports that help them troubleshoot system issues and track system performance.

The syslog file is an indispensable component of Linux system administration, and understanding how to use it effectively is vital for any Linux administrator.

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