Linux System Monitoring

• System monitoring helps with identifying bottlenecks, optimizing performance, and troubleshooting issues.

Monitoring CPU Usage

• The top command is used for real-time process monitoring.
• It displays active processes, CPU, and memory usage.
• Press "q" to exit, "k" to kill a process, and "r" to renice a process in top.
• The command htop provides a better visual representation of system resource usage.
• Install htop with sudo apt install htop.
• The mpstat command is part of the sysstat package.
• mpstat is used to monitor CPU usage per core in real-time.
• Use mpstat -P ALL 1 to view all CPU cores.
• The uptime command provides a quick summary of how long the system has been running and its load average.

Monitoring Memory Usage

• The free command displays memory statistics.
• free checks the RAM (memory) and swap usage on a Linux system.
• Use free -m for output in megabytes.

System Performance Overview

• The command vmstat (Virtual Memory Statistics) provides a detailed overview of system performance.
• This includes CPU, memory, swap, disk, and process activity.
• Use vmstat 2 5 to update every 2 seconds, 5 times.

Monitoring Disk Usage

• The df (Disk Filesystem) command displays the disk space usage on Ubuntu.
• Command df -h shows disk usage in human readable format.
• Command df -h /home shows disk usage for the /home directory.

Directory Disk Usage

• The du (Disk Usage) command checks how much disk space directories and files are consuming.
• Command du -sh /home shows the total disk usage for /home in summary format.
• Command du -h /home shows disk usage for /home in human readable format.
• Command du -ah /home | sort -rh | head -10 lists the 10 largest files/directories in /home.

Disk I/O Statistics

• The iostat command monitors disk performance.
• iostat helps analyze disk read/write speeds, utilization, and performance bottlenecks.
• Command iostat -dx 1 shows detailed disk I/O statistics, updating every 1 second.

Monitoring Network Usage

• The netstat (Network Statistics) command displays active network connections, routing tables, and interface statistics and more.
• The option netstat -tulnp shows listening ports.

Monitoring Socket Statistics

• The ss command (Socket Statistics) is a faster and more efficient alternative to netstat for displaying network socket information.
• Use ss -tulnp to show listening ports.

Real-time Network Bandwidth Monitoring

• The iftop is a real-time network monitoring tool.
• iftop shows bandwidth usage on an interface by monitoring the traffic between hosts.
• Use sudo iftop to run command.

Per Process Bandwidth Usage

• nethogs is also a real-time network monitoring tool
• nethogs displays the bandwidth usage per process.
• Use sudo nethogs to run the command.

Monitoring Logs

• journalctl is the command-line utility used to query and view logs stored in the systemd journal.
• Use the command journalctl -xe to show logs with explanations and extra details.

Live System Log Monitoring

• tail -f is a command used to continuously monitor log files in real time.
• tail -f allows for watching new log entries as they are added.
• Command tail -f /var/log/syslog monitors the system log file continuously.