ps Command Guide

Basic Usage

Without options, ps shows processes for the current terminal.

ps

Output columns: PID (Process ID), TTY (Terminal), TIME (CPU time), CMD (Command).

Common Option Styles

ps supports three option styles: Unix (-), BSD (no dash), and GNU (--).

View All Processes

BSD style (most common)

ps aux

Columns: USER, PID, %CPU, %MEM, VSZ, RSS, TTY, STAT, START, TIME, COMMAND

Unix style

ps -ef

Columns: UID, PID, PPID, C, STIME, TTY, TIME, CMD

Understanding Output Columns

Process States (STAT column)

Filtering Processes

By user

# Processes for a specific user
ps -u username

# Or with BSD style
ps aux | grep username

By process name

# Using grep
ps aux | grep nginx

# Using pgrep
pgrep -a nginx

By PID

ps -p 1234

# Multiple PIDs
ps -p 1234,5678,9012

Process Tree

# Show process hierarchy
ps --forest

# Or combined with aux
ps auxf

# Or use pstree for better visualization
pstree

Custom Output Format

# Select specific columns
ps -eo pid,user,%cpu,%mem,command

# Sort by memory usage
ps -eo pid,user,%mem,command --sort=-%mem

# Sort by CPU usage
ps -eo pid,user,%cpu,command --sort=-%cpu

Practical Examples

Find top CPU consuming processes

ps aux --sort=-%cpu | head -11

Find top memory consuming processes

ps aux --sort=-%mem | head -11

Find zombie processes

ps aux | awk '$8 ~ /Z/ { print }'

Count processes by user

ps -eo user | sort | uniq -c | sort -rn

Monitor a specific process

watch -n 1 "ps -p 1234 -o pid,%cpu,%mem,etime"

Find parent process

ps -o ppid= -p 1234

Show threads

ps -eLf

Related Commands

Summary

ps is essential for process monitoring. Key takeaways:

• Use ps aux for comprehensive process listing
• Use ps -ef for Unix-style output with PPID
• Use --sort to sort by CPU or memory
• Use -o for custom output format
• Combine with grep to filter by name