How Computer Programs Run on Linux

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How Computer Programs Run on Linux

What's a Computer Program?

Think of a program like a recipe. When you "run" it, the computer follows the instructions step by step. On Linux, we call this running recipe a process.

Real Life Examples

  • Web browser (like Firefox)
  • Game (like Minecraft)
  • Text editor (like Notepad)

The Life of a Program

  1. 📥 Loading: Computer copies the program from storage to memory
  2. 🏃 Running: Computer follows the program's instructions
  3. 🛑 Stopping: Program finishes or gets canceled

Program Settings (Environment Variables)

These are like special notes the program reads before starting:

  • LANG=en_US - Sets language to English
  • HOME=/users/bob - Shows where your files are stored

How Programs Talk to the Computer

Programs use special requests called system calls:

  • 📖 read - Read a file
  • ✏️ write - Save changes
  • 🚪 open - Access a device

Emergency Signals

Like a walkie-talkie for programs:

  • 🚨 Ctrl+C = "Stop immediately!" (SIGINT)
  • 💥 "Terminate now!" (SIGKILL)

Sharing Between Programs

Programs can share memory like a shared notebook:

  1. Create shared space (shmget)
  2. Connect to it (shmat)
  3. Write/read messages
  4. Disconnect when done (shmdt)

Common Questions

Why do some programs become zombies?

When programs finish but aren't cleaned up properly - use the wait command to fix!

How to see what a program is doing?

Use strace - it's like X-ray glasses for programs!

Can programs share secrets?

Yes! That's why we have special security like ASLR (memory scrambling).

Best Tips

  • 🔒 Always check program permissions
  • 🧹 Clean up finished programs
  • 🐞 Use strace to find problems

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