Process Monitoring: top, htop & Background Jobs

In Plain English

Real-time process monitors like `top` and `htop` display dynamic system metrics including CPU utilization, memory consumption, load averages, and per-process threads. In Bash, jobs can be sent to the background with `&`, suspended with Ctrl+Z, and resumed via `bg` and `fg`.

The Mental Model

"`ps` is a static photograph of traffic at a single second; `top` is a live CCTV video feed continuously tracking cars driving on the highway."

Deep Dive: How It Works

Load Average: Three numbers representing average runnable tasks over 1, 5, and 15 minutes. A load of 1.0 on a 1-core CPU indicates 100% capacity.

Job Control: Append `&` to run commands in background; `jobs` lists active jobs; `fg %1` brings job 1 to foreground; `bg %1` resumes job in background.

Batch Mode top: `top -b -n 1` dumps a single non-interactive batch frame ideal for parsing in monitoring scripts.

Syntax Blueprint

command &
jobs -l
fg %1
bg %1
top -b -n 1 | head -n 15

Use & to run background jobs and top in batch mode (-b) for scriptable metrics.

Core Rules to Remember

Background Execution: Running `python script.py &` frees the terminal prompt immediately.

nohup / disown: Prevents background jobs from terminating when closing the terminal session (SIGHUP signal).

Batch Mode top: `top -b -n 1` enables programmatic system health monitoring in CI/CD pipelines.

Common Beginner Traps & How to Fix Them

Mistake:Closing the SSH terminal and having background jobs suddenly die.

Why it happens: Closing the terminal sends SIGHUP (hangup) signal to all child processes.

How to fix: Run with `nohup command &` or `disown -h` to detach from terminal sessions.

Pro Tip: Use `watch -n 2 "ps aux --sort=-%cpu | head -n 6"` to build a custom real-time top CPU consumer monitor.

Live Interactive Example

Hit Run Code to see it live

Managing Background Jobs with jobs, bg, and fg

Git 2.45 / CLI

Output Console

Click "Run Code" to view the rendered output.

How it works: $! captures the PID of the most recently spawned background process, and wait pauses until it completes.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Run a Background Job and Wait

Run `sleep 1 &` in the background.
Capture PID using `$!` and wait for it with `wait $!`.
Echo "Done waiting".

Sandbox Output

Click "Run & Check" to test your solution.

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