/var/log/syslog: Explanation & Insights

Contains important message logs

The file /var/log/syslog is one of the most important log files in a Linux system. It is a system log file where your system writes all message logs except for authentication messages, which are written in a different log file. These logs contain messages from the Kernel, daemon, and other system services. Understanding this file can help you diagnose many system issues including hardware failure and system crashes.

What is in the /var/log/syslog file?

The /var/log/syslog file contains a chronological record of system messages and warnings. Each log entry in the file includes the date and time of the message, the name of the machine, the process that generated the message, and the actual message. The log entries are written in plain text, which makes it easy to read and understand the messages.

Importance of /var/log/syslog

This file plays a crucial role in system administration by providing a historical record of system activities. By monitoring and reviewing the /var/log/syslog, system administrators can detect system errors, security breaches, and even predict the possibility of future system failures.

How to Access the /var/log/syslog file

To view the content of the /var/log/syslog file, you can use commands like cat, less, or tail. For example, to view the last 10 lines of this file, you can use the tail command as follows:

sudo tail -n 10 /var/log/syslog

Example of /var/log/syslog file content

Here is an example of what you might see in /var/log/syslog:

Jun  5 15:45:01 myserver CRON[12345]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
Jun  5 15:46:39 myserver kernel: [123456.789012] usb 1-1.2: new high-speed USB device number 5 using ehci-pci
Jun  5 15:46:39 myserver kernel: [123456.890123] usb 1-1.2: New USB device found, idVendor=abcd, idProduct=1234
Jun  5 15:46:39 myserver kernel: [123456.991234] usb 1-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3

Common Problems and Solutions

Some common problems that can be diagnosed by checking the /var/log/syslog include:

High CPU Usage: If your system is slowing down or the CPU usage is high, checking the syslog can help identify the process causing the high CPU usage.
Device Failure: If a device connected to the system is not working, the syslog can show if the system is having trouble communicating with the device.
Unexpected Shutdowns or Restarts: If the system is shutting down or restarting unexpectedly, the syslog can provide clues as to what is causing the issue.

Conclusion

The /var/log/syslog file is a vital tool in diagnosing and solving many system-related issues on a Linux server. Understanding this file and knowing how to interpret its contents is an essential skill for any system administrator.