Software & AppsOperating SystemLinux

Why is my var/log/syslog file growing indefinitely in size?

Ubuntu 9

Understanding the issue of an indefinitely growing /var/log/syslog file is crucial for system administrators and users alike. This article will provide a comprehensive guide on why this happens and how to resolve it.

Quick Answer

The /var/log/syslog file can grow indefinitely due to repeated logging of errors from the same source. To resolve the issue, you can identify the source of the error by monitoring the logs using the tail -f /var/log/syslog command. Once identified, you can clear the file using either the sudo cat /dev/null > /var/log/syslog or sudo truncate -s 0 /var/log/syslog command. However, clearing the file may not be a permanent solution, and it’s important to investigate and address the underlying problem to prevent the issue from recurring.

What is the /var/log/syslog file?

The /var/log/syslog file in Linux-based systems is a log file that stores messages from your system’s syslogd daemon, including system error messages, startup messages, and system logs. This file is crucial for troubleshooting and monitoring system performance.

Why does it grow indefinitely?

The /var/log/syslog file can grow indefinitely due to various reasons. One common cause is repeated logging of errors from the same source. For instance, error reports related to wifi monitoring interface mon0 or VPN interfaces like tun0 can cause the syslog file to grow significantly.

Identifying the Source of the Error

To identify the source of the error, you can monitor the logs using the tail -f /var/log/syslog command. The tail command outputs the last part of files, and the -f option allows you to follow the output. This command will display the most recent entries to the syslog file in real-time, helping you identify the source of the error.

Clearing the /var/log/syslog file

Once the source of the error is identified, the next step is to clear the /var/log/syslog file to free up disk space. However, due to its massive size, clearing the file can be challenging. Here are two approaches:

  • Use the command sudo cat /dev/null > /var/log/syslog. The cat command concatenates and displays files. /dev/null is a special file that discards all data written to it. The > operator redirects the output. In this command, we’re essentially redirecting nothing into syslog, effectively clearing it.
  • Alternatively, use the command sudo truncate -s 0 /var/log/syslog. The truncate command shrinks or extends the size of a file to the specified size. The -s option is used to specify the size. In this case, we’re setting the size to 0, effectively clearing the file.

Addressing the Underlying Problem

Clearing the syslog file may not be a permanent solution. It’s crucial to investigate the cause of the error and fix the underlying problem. This could involve:

  • Checking the /var/lib/logrotate/status file to ensure proper rotation of logs. Log rotation is the practice of archiving old log files to prevent them from consuming too much disk space.
  • Reviewing the contents of the syslog file to identify system issues.
  • Examining the running processes and services for any potential loops or errors.

Setting up a Regular Check

In some cases, it may be necessary to create a script to regularly check and clear the syslog file if it exceeds a certain size. This can be done by creating a script file, such as clearlog.sh, and adding a postrotate section in the logrotate configuration file /etc/logrotate.d/logs.

Conclusion

The issue of an indefinitely growing /var/log/syslog file can be a significant problem, consuming valuable disk space and potentially slowing down your system. However, with the right knowledge and tools, you can identify the source of the error, clear the file, and take steps to prevent the issue from recurring.

How can I check the size of the `/var/log/syslog` file?

You can check the size of the /var/log/syslog file by using the ls -lh /var/log/syslog command. This will display the size of the file in a human-readable format.

Can I delete the `/var/log/syslog` file to free up disk space?

It is not recommended to delete the /var/log/syslog file directly. Instead, you should clear its contents using the methods mentioned in the article. Deleting the file itself can cause issues with logging and monitoring system performance.

How often should I check the `/var/log/syslog` file for errors?

The frequency of checking the /var/log/syslog file for errors may vary depending on your system and usage. However, it is recommended to check it regularly, especially when troubleshooting system issues or monitoring system performance.

How can I prevent the `/var/log/syslog` file from growing indefinitely in the future?

To prevent the /var/log/syslog file from growing indefinitely, you can implement log rotation. This involves archiving old log files and setting a limit on the size of the syslog file. You can configure log rotation using the logrotate utility and modifying the /etc/logrotate.d/logs file.

What should I do if the `/var/log/syslog` file keeps growing even after clearing it?

If the /var/log/syslog file continues to grow after clearing it, it indicates an underlying problem that needs to be addressed. You should investigate the cause of the error, review the syslog file contents, and examine running processes and services for any potential loops or errors.

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