The ps command displays process information from the process table.

It is commonly used for:

• Viewing running processes
• Checking CPU and memory usage
• Filtering for specific users or commands
• Finding process IDs before signaling with kill or pkill

Overview

There are two widely used syntax styles:

• UNIX style options: ps -ef
• BSD style options: ps aux

Both are valid on most Linux systems.

Syntax

ps [options]

Command Quick Reference

Command	Purpose
ps aux	Full process list in BSD format
ps -ef	Full process list in UNIX format
ps -u <user>	Show processes for a user
ps -p <pid>	Show one process by PID
ps -C <name>	Show processes by exact command name
ps -eo ...	Custom output columns

Core Workflows

List All Processes

ps aux
ps -ef

Filter by User or Command

ps -u root
ps -C nginx
ps aux | grep sshd

Inspect Specific Process IDs

ps -p 1234
ps -fp 1234

-f adds full-format details (UID, PID, PPID, start time, command).

Custom Output Columns

ps -eo pid,ppid,user,%cpu,%mem,etime,cmd --sort=-%cpu

This is useful when building repeatable diagnostics.

Useful Options

Option	Meaning
a	Show processes for all users (BSD style)
u	User-oriented output
x	Include processes without a controlling terminal
-e	Select all processes
-f	Full format listing
-o	Custom output format
--sort	Sort by field
-p	Select specific PID(s)

Examples

ps aux
ps -ef
ps -eo pid,user,%cpu,%mem,cmd --sort=-%mem | head

Troubleshooting

grep Matches Itself

ps aux | grep nginx may include the grep process line.

Safer alternatives:

pgrep -af nginx
ps -C nginx -f

Output Differences Across Systems

Some column names and defaults vary by distro and procps version. Use explicit output format (-o) for stable automation.

Best Practices

1. Prefer explicit output columns for scripts (ps -eo ...).
2. Use pgrep when your goal is PID lookup by name/pattern.
3. Combine with head, sort, and grep for focused diagnostics.
4. Avoid parsing human-formatted defaults in automation.

Related Commands

• pgrep: Find process IDs by name/pattern
• kill: Send signals to specific PIDs
• pkill: Send signals by process name/pattern
• top or htop: Interactive process monitoring