Linux Top Command Usage Tutorial and Tips

1. Basic Usage

Starting top

# Start directly
top

# Set refresh interval (seconds)
top -d 2

# Show only processes of a specific user
top -u username

# Hide idle processes on startup
top -i

2. Overview of the Top Interface

top - 10:30:00 up 10 days,  1:15,  1 user,  load average: 0.05, 0.10, 0.15
Tasks: 150 total,   1 running, 149 sleeping,   0 stopped,   0 zombie
%Cpu(s):  1.5 us,  0.5 sy,  0.0 ni, 98.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :   7952.0 total,    512.0 free,   4096.0 used,   3344.0 buff/cache
MiB Swap:   2048.0 total,   2048.0 free,      0.0 used.   3500.0 avail Mem

Explanation of Each Area:

• • First Line: System time, uptime, number of users, load average
• • Second Line: Process statistics (total, running, sleeping, stopped, zombie)
• • Third Line: CPU usage statistics
• • Fourth Line: Physical memory usage
• • Fifth Line: Swap usage

3. Interactive Commands (Used While top is Running)

Process Sorting

P - Sort by CPU usage (default)
M - Sort by memory usage
T - Sort by running time
N - Sort by PID

Display Options

l - Toggle load average line display
t - Toggle task/CPU state line display
m - Toggle memory information line display
1 - Expand to show usage for each CPU core

Process Operations

k - Kill process (input PID and signal)
r - Reset process priority (nice value)

Refresh Control

Spacebar - Refresh immediately
s - Change refresh interval (seconds)

4. Practical Tips

Batch Mode (For Scripts)

# Display once and then exit
top -n 1 -b

# Save to file
top -n 1 -b > top_output.txt

# Show only the top 10 processes
top -n 1 -b | head -20

Monitor Specific Processes

# Monitor specific PID
top -p 1234

# Monitor multiple PIDs
top -p 1234,5678,9012

# Monitor processes with names containing nginx
top -p $(pgrep nginx | tr '\n' ',' | sed 's/,$//')

5. Field Explanation and Customization

Display Full Command Line

While running top, press: c

Change Display Fields

f - Enter field management interface
Use up and down keys to select fields, press spacebar to toggle display
d - Select sorting field

Common Field Explanations

• • PID: Process ID
• • USER: Process owner
• • PR: Priority
• • NI: Nice value
• • VIRT: Virtual memory usage
• • RES: Physical memory usage
• • SHR: Shared memory size
• • S: Process state
• • %CPU: CPU usage percentage
• • %MEM: Memory usage percentage
• • TIME+: Cumulative CPU time

6. Advanced Usage

Save Configuration

# After adjusting the display in top
Press W (uppercase) to save configuration to ~/.toprc

Color Display

# Enable color display
top -z

# Switch color during runtime: press Z

Tree View of Processes

# Press: V during runtime

7. Practical Application Examples

Monitor System Performance

# Refresh every 5 seconds, show only important information
top -d 5 -i

# Sort by memory, monitor memory usage
top -o %MEM

Find Processes with Highest Resource Usage

# Sort by CPU
top -o %CPU

# Sort by memory
top -o %MEM

Use in Scripts

#!/bin/bash
# Get the process with the highest CPU usage
HIGH_CPU_PROC=$(top -bn1 -o %CPU | head -8 | tail -1 | awk '{print $12}')
echo "Process with highest CPU usage: $HIGH_CPU_PROC"

# Get memory usage percentage
MEM_USAGE=$(top -bn1 | grep "MiB Mem" | awk '{print $8/$4*100}')
echo "Memory usage: ${MEM_USAGE}%"

8. Recommended Alternative Tools

# htop - Enhanced version of top
htop

# atop - More detailed system monitoring
atop

# nmon - Professional performance monitoring tool
nmon

Summary of Common Shortcuts

• • q – Exit
• • h – Help
• • P/M/T – Sort by CPU/memory/time
• • k – Kill process
• • r – Adjust priority
• • 1 – Show each CPU core
• • z – Toggle color display

Mastering these top command usage tips can help you monitor system performance more effectively and quickly locate problematic processes.