In Unix/Linux system administration, which command is used to display the characteristics and current status of running processes (for example, PID, TTY, CPU time, and the command)?

Introduction / Context:
Being able to view process characteristics is essential for Unix/Linux troubleshooting and performance tuning. Administrators and developers rely on a standard tool to see a snapshot of running processes, including process IDs, controlling terminals, resource usage, parent relationships, and the command that launched each process.

Given Data / Assumptions:

• You are using a Unix-like shell such as bash or zsh.
• You wish to inspect live process information like PID, TTY, CPU time, and command.
• No third-party utilities are assumed; only core system tools.

Concept / Approach:
The command 'ps' (process status) prints process attributes in various formats. Common invocations include 'ps aux' (BSD style) to list all processes system-wide and 'ps -ef' (SysV style) for a full-format listing. Options like '-o' allow custom column selection, while filters such as '-u user' or a specific PID restrict the output to what you need.

Step-by-Step Solution:

Verification / Alternative check:
Cross-check PIDs reported by 'ps' with corresponding entries under '/proc/' on Linux, or use dynamic viewers like 'top'/'htop' to confirm that the same processes are present. Exit statuses and process hierarchies should align across tools.

Why Other Options Are Wrong:

• pid: This is a process identifier concept, not a listing command.
• du: Reports disk usage; unrelated to process inspection.
• au: Not a standard command for process display.
• None of the above: Incorrect because 'ps' is precisely the required tool.

Common Pitfalls:
Mixing BSD and SysV option styles (some flags differ), assuming 'ps' auto-updates (it does not; it is a snapshot), or forgetting to elevate privileges when listing processes owned by other users and expecting complete results.

Final Answer:
ps