2.5 Process Control

Every running program is a process with a unique PID (Process ID).

Viewing Processes

• top: Real-time view of system resources (CPU/RAM) and processes. Press q to quit.
• htop: A prettier, more interactive version of top (often needs install).
• ps: Snapshot of current processes.
  • ps aux (BSD style) or ps -ef (Standard): Shows ALL processes.

Killing Processes

Creating a “zombie” or stopping a stuck program.

• kill <PID>: Send SIGTERM (15). Asks nicely to stop.
• kill -9 <PID>: Send SIGKILL (9). Forces stop immediately (can lose data).

  Danger

  Use kill -9 only as a last resort, as it can cause data loss or corruption.
• killall <name>: Kill processes by name instead of ID.

Background Jobs

When you run a command, it occupies the terminal.

1. Background (&):

   sleep 100 &

   Runs in background. Terminal is free.

2. Foreground (fg) to Background (bg):

   • Run a command (e.g., top).
   • Press Ctrl + Z to suspend it.
   • Type bg to resume it in background.
   • Type fg to bring it back to foreground.

3. Jobs:

   • Type jobs to list background jobs in current terminal session.