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Chapter 4.2 - Process Visualization

Learning Objectives​

By the end of this chapter, you will be able to:

  • Use ps effectively
  • Monitor with top and htop
  • Understand the displayed information
  • Filter and sort processes

ps - Process Listing​

Basic Syntax​

# All processes
ps aux

# Current user's processes
ps

# BSD format
ps aux

# Standard format
ps -ef

Useful Options​

# Custom format
ps -eo pid,ppid,user,cmd,%mem,%cpu,etime

# By user
ps -u user1
ps aux | grep user1

# By command
ps aux | grep apache

# Process tree
ps auxf
ps -ejH
ps --forest

# Processes from a terminal
ps -t tty1

Important Columns​

  • PID: Process ID
  • PPID: Parent Process ID
  • USER: Owner
  • %CPU: CPU usage
  • %MEM: Memory usage
  • STAT: State (R, S, T, Z, D)
  • START: Start time
  • TIME: CPU time used
  • COMMAND: Full command

top - Real-Time Monitoring​

Interactive Interface​

top

Header displays:

  • System time and uptime
  • Number of users
  • Load average
  • Process states
  • CPU and memory usage

Body displays:

  • List of processes
  • Sorted by CPU (default)

Commands in top​

# Navigation
h          # Help
q          # Quit
Space      # Refresh immediately

# Sorting
P          # By CPU (default)
M          # By memory
T          # By CPU time
N          # By PID
k          # Kill a process (asks for PID)
r          # Renice (change priority)

# Filters
u          # Filter by user
o          # Filter by criteria
=          # Reset filters

# Display
1          # Show all CPUs
f          # Choose columns
W          # Save configuration

Command Line Options​

# Custom update
top -d 5           # Every 5 seconds

# By user
top -u user1

# Specific process
top -p 1234,5678

# Batch mode (for scripts)
top -b -n 1 > processes.txt

htop - Enhanced Version​

Installation​

# Ubuntu/Debian
sudo apt install htop

# Red Hat/CentOS
sudo yum install htop
# or
sudo dnf install htop

Advantages​

  • Colorful and intuitive interface
  • Arrow key navigation
  • Easy filtering
  • Visual process tree
  • Progress bars

Usage​

htop

Shortcuts:

  • F2: Setup
  • F3: Search
  • F4: Filter
  • F5: Tree view
  • F6: Sort
  • F9: Kill process
  • F10: Quit
  • Space: Mark process

Other Tools​

pstree - Process Tree​

# Simple tree
pstree

# With PIDs
pstree -p

# With users
pstree -u

# By user
pstree -u user1

pgrep - Search by Name​

# Find PID by name
pgrep apache
pgrep -u user1 bash

# Show name too
pgrep -l apache

# Count
pgrep -c apache

pidof - Program PID​

# Program PID
pidof apache2
pidof -s apache2  # Single PID

Detailed Information​

/proc/[PID]/​

Directory with information about each process:

# View process info
cat /proc/1234/status
cat /proc/1234/cmdline
cat /proc/1234/environ
cat /proc/1234/io        # I/O
cat /proc/1234/fd/      # Open files

stat and status​

# Detailed status
cat /proc/1234/status

# Raw information
cat /proc/1234/stat

Summary​

In this chapter, you learned:

ps: Process listing, numerous options
top: Real-time monitoring, interactive interface
htop: Enhanced version, more user-friendly
pstree: Process tree
pgrep/pidof: Search processes by name
/proc/: Detailed process information

Next Steps​

Chapter 4.3: Process Control
Chapter 4.4: Priorities and Nice Values

Chapter created on: December 2024