Mastering Linux ps Command Guide | Generated by AI

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I’ll give you a comprehensive introduction to the ps command and its options for listing processes.

What is ps?

The ps command displays information about active processes on a Unix/Linux system. It’s one of the most fundamental tools for process management and system monitoring.

Basic Usage

The simplest form shows processes for the current user in the current terminal:

ps

Common Option Styles

The ps command has three different option styles that can be mixed:

1. Unix options - preceded by a dash (e.g., -e)
2. BSD options - no dash (e.g., aux)
3. GNU long options - two dashes (e.g., --forest)

Most Useful Commands

See all processes for all users:

ps aux          # BSD style
ps -ef          # Unix style

See processes in a tree/hierarchy:

ps auxf         # BSD style with forest view
ps -ef --forest # Unix style with tree

See processes for a specific user:

ps -u username
ps aux | grep username

See processes by PID:

ps -p 1234
ps -p 1234,5678,9101  # multiple PIDs

Key Options Explained

BSD Style (no dash)

• a - show processes for all users
• u - display user-oriented format (shows owner, CPU%, memory%, etc.)
• x - include processes without a controlling terminal
• f - ASCII art process hierarchy/forest
• w - wide output (don’t truncate command lines)
• ww - unlimited width

Unix Style (with dash)

• -e - select all processes
• -f - full format listing
• -l - long format
• -u user - processes for specific user
• -p pid - specific process ID(s)
• -C command - processes by command name
• -o format - custom output format
• --forest - ASCII art process tree

Understanding the Output

When you run ps aux, you’ll see columns like:

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

• USER - process owner
• PID - process ID
• %CPU - CPU usage percentage
• %MEM - memory usage percentage
• VSZ - virtual memory size (KB)
• RSS - resident set size (physical memory in KB)
• TTY - controlling terminal (? means no terminal)
• STAT - process state:
  • R - running
  • S - sleeping (interruptible)
  • D - sleeping (uninterruptible, usually I/O)
  • T - stopped
  • Z - zombie
  • < - high priority
  • N - low priority
  • s - session leader
  • + - foreground process group
• START - when process started
• TIME - cumulative CPU time
• COMMAND - command with arguments

Custom Output Formats

You can customize which columns to display:

ps -eo pid,user,%cpu,%mem,command
ps aux --sort=-%cpu | head    # top CPU users
ps aux --sort=-%mem | head    # top memory users

Practical Examples

Find a specific process:

ps aux | grep firefox

Show threads:

ps -eLf          # all threads
ps -T -p 1234    # threads for specific PID

Watch processes in real-time:

watch -n 1 'ps aux --sort=-%cpu | head -20'

See process with full command line:

ps auxww | grep process_name

Count processes:

ps aux | wc -l

See process tree from specific process:

ps -ef --forest | grep -A 5 process_name

Commonly Used Combinations

ps aux              # Everything, detailed
ps -ef              # Everything, different format
ps auxf             # Everything with hierarchy
ps -u $(whoami)     # Just your processes
ps -C httpd         # All httpd processes
ps -p $$            # Current shell process

Tips

• For real-time monitoring, consider using top or htop instead
• Combine with grep, sort, head, and tail for filtering
• Use pgrep for simpler process searching by name
• The output can be piped to awk or cut for specific fields

The ps command is incredibly versatile. Start with ps aux or ps -ef for general overview, then add options as needed for more specific information.

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