As an admin for a Linux server, you are always engaged in monitoring. You use the default system tools but also can utilize more complex monitoring tools.
toptop and you’ll see a list of processes sorted by CPU usage by default.-d [seconds] - Set delay between updates.-o [field] - Sort by a specific field, e.g., memory usage.htoptop, with a better interface and more options.htop and you get a color-coded, more user-friendly display.vmstat (Virtual Memory Statistics)vmstat [delay] [count]vmstat 5 10 will report stats every 5 seconds, 10 times.iostat (I/O Statistics)iostat to view CPU and I/O statistics.iostat 2 will refresh every 2 seconds.netstat / ssnetstat -tuln (to view listening ports).ss -tuln (modern replacement for netstat).sar (System Activity Report)sar -u 5 (CPU utilization every 5 seconds).sar -r (memory usage stats).dmesgdmesg (for a full dump), dmesg -w (to follow live updates).journalctljournalctl -xe (view errors).journalctl -f (follow live log output).nmonnmon and press different keys (e.g., c for CPU, m for memory).sudo apt install nmon.glancesglances to see system metrics.iftopsudo iftop to display network activity on a given interface.-i [interface] to monitor a specific network interface.nloadnload and see network activity in a text-based graph.tcpdumpsudo tcpdump -i eth0 to capture packets on interface eth0.psps aux to view all running processes.ps -eF to display extended process information.kill and killallkill [PID] sends a signal to a specific process by ID.killall [process_name] kills all instances of a process.