top

Overview

The top command provides a dynamic real-time view of running processes. It shows system summary information and a list of processes currently being managed by the Linux kernel.

Syntax

top [options]

Common Options

Option Description
-b Batch mode
-n num Number of iterations
-p pid Monitor PID
-u user User processes
-H Show threads
-i Idle processes
-c Command line
-w Output width
-d delay Update delay
-o field Sort field
-U user User filter
-E scale Memory scale

Interactive Commands

Key Action
h Help
q Quit
k Kill process
r Renice process
f Fields management
o Sort field
u User filter
M Sort by memory
P Sort by CPU
T Sort by time
W Write config

Key Use Cases

  1. System monitoring
  2. Resource tracking
  3. Process management
  4. Performance analysis
  5. Troubleshooting

Examples with Explanations

Example 1: Basic Usage

top

Show system status

Example 2: Specific User

top -u username

Show user processes

Example 3: Batch Mode

top -b -n 1

Single iteration output

Common Usage Patterns

  1. Monitor PID:

    top -p 1234

  2. Sort by memory:

    top -o %MEM

  3. Update faster:

    top -d 0.5

Header Information

  1. System uptime
  2. Load averages
  3. CPU states
  4. Memory usage
  5. Swap usage

Additional Resources

Best Practices

  1. Regular monitoring
  2. Set refresh rate
  3. Use filters
  4. Check trends
  5. Document issues

Security Considerations

  1. Process visibility
  2. User permissions
  3. Resource impact
  4. Signal handling
  5. Configuration

Troubleshooting

  1. High CPU use
  2. Memory leaks
  3. Process states
  4. System load
  5. Performance issues

Output Fields

  1. PID
  2. USER
  3. PR/NI
  4. VIRT/RES/SHR
  5. S (Status)