Process Management

On Linux, what single file attribute distinguishes a runnable program from an ordinary data file, and why does that make file extensions irrelevant for execution?

A Windows user asks where the .exe files live on a Linux box. What is the accurate answer, including the one real exception?

You just compiled a binary in your current directory and typing its name gives "command not found". Why, and what is the fix?

From a desktop terminal, what does xdg-open do that plain execution does not, and what is its portable-looking alias on some distros?

In a terminal, what is the difference between a foreground and a background job, and how do you move an already-running foreground command into the background without killing it?

Plain ps in a terminal shows only a handful of processes on a busy graphical system. Why, and what invocation lists everything?

You want to see which processes are hammering the CPU right now, updating live. Which tool beats ps for this, how does it order output, and how do you act on a runaway process from inside it?

In top or ps you see a process in state S. Does that mean it's broken or hung, and how does it differ from states R and T?

The CPU looks idle but the machine crawls, and top's CPU sort tells you nothing useful. Which monitor should you reach for instead, and how do you narrow its output?

An unmount fails because a directory is "in use" but you can't see any obvious program touching it. Which command reveals the culprit, and what non-obvious thing counts as "using" it?

What single process sits at the root of the Linux process tree, when is it started, and which tool visualizes the hierarchy?

A process ignores your kill and keeps eating memory. What signal did kill send by default, what should you escalate to, and why not lead with the harsher one?

You try to kill another user's runaway process and get "Operation not permitted". Why, and who is allowed to do it?

You have five stuck Firefox windows and don't want to hunt down five PIDs. Which command targets them by name, and what is the side effect to watch for?

A text-based command in the foreground is stuck and you want it gone instantly without opening another terminal. What's the quickest fix?

You want to cap how much memory or how large a file a shell and its child programs can create. Which command does this, and where is it typically configured system-wide?

You launch a backup so it won't slow down interactive work. Using nice, which number means "low priority", and which way does the scale run?

A long-running job is already started and you realize it should be lower priority. Which command adjusts it, and what can a non-root user NOT do with it?

Your backup saturates the disk and slows time-critical services even though CPU is fine. nice didn't help — what's the right tool, and why is it different?

Coming from Windows, what Linux term corresponds to a "service", and when do these processes usually start?

For each of these roles, which daemon runs it: incoming SSH, web server, MySQL/MariaDB, print spooling, DNS, outgoing mail?

In ps axu you see names in square brackets like [kswapd0] and [kworker/0]. What are these, and can you kill or reconfigure them like normal daemons?

With systemctl, what is the difference between starting a service and enabling it, and which single flag does both at once?

At the OS level, when does a program file actually become a 'process', and what is a process responsible for?

You start a long command with & but its status messages keep cluttering the terminal. How do you keep it in the background without the noise?

top works, but you want to scroll sideways through long command lines and up/down the process list. Which tool gives you that, and what's the catch?

You know a program's name and just need its PID(s) for a script, without eyeballing ps output. Which command is built for that?

fuser shows no process using a file you're clearly editing in a text editor. Is fuser broken, and why does this happen?

Several processes share the same name, yet the init system can still stop exactly the right one. What mechanism makes that possible?

A graphical window is frozen and you'd rather point-and-click than hunt for its PID. Which command lets you do that, and what's the hard requirement?

A desktop program hangs so badly it grabs the keyboard/mouse and the GUI stops responding to input. What key combination can rescue you?

How does the kernel expose live data about each running process, and where do ps/top get details like a process's original command line?