Essential Linux Commands for Diagnosing Production Issues

This article introduces several frequently used Linux commands for diagnosing online production issues.

top – System Overview

The top command provides a snapshot similar to Windows Task Manager, showing overall system load and per‑process resource usage.

top - 18:14:58 up 112 days, 1:35, 1 user, load average: 0.00, 0.10, 0.11

Key fields:

Current time

Uptime (days, hours, minutes)

Number of logged‑in users

Load averages for the last 1, 5, and 15 minutes (values >1 indicate overload)

Tasks: 225 total, 1 running, 224 sleeping, 0 stopped, 0 zombie

Task line explains total processes, how many are running, sleeping, stopped, or zombie.

CPU Usage

Cpu(s): 1.8%us, 0.9%sy, 0.0%ni, 97.1%id, 0.1%wa, 0.0%hi, 0.1%si, 0.0%st

Fields:

us – user‑space CPU percentage

sy – kernel‑space CPU percentage

ni – processes with altered priority

id – idle CPU

wa – I/O wait

hi – hardware interrupts

si – software interrupts

Memory Usage

Mem: 32879852k total, 23633040k used, 9246812k free, 311552k buffers

Breakdown of physical memory: total, used, free, and kernel buffers. Available memory can be calculated as free + buffers + cached.

Swap Usage

Swap: 4194300k total, 255104k used, 3939196k free, 10422508k cached

Shows virtual memory statistics.

Other Useful Commands

iostat

Displays CPU and I/O statistics.

iostat -d

iostat -d 2 2

iostat -x 1 2

netstat

Shows network connections; pay special attention to the number of ESTABLISHED connections.

netstat -na | grep ESTABLISHED | awk '{print $5}' | awk -F: '{print $1}' | sort | uniq -c

netstat -na | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'

df -h

Displays disk space usage in a human‑readable format.

du -sh

Shows the size of a directory or file; variations include du --max-depth=2 --block-size=M or ll --block-size=M.