System processes and memory usage

4.3 Where Data is Stored (Weight: 3)

📘Linux Essentials (LPI 010-160)

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1. What is a Process?

• A process is basically a program that is running.
• Examples of processes:
  • Running a text editor like gedit or nano.
  • A web server process like apache2.
  • A backup script running automatically at night.
• Each process has:
  • A unique ID called PID (Process ID).
  • Memory usage: How much RAM it is using.
  • CPU usage: How much processor power it is using.
  • State: Running, sleeping, stopped, etc.

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2. Viewing Processes

Linux provides commands to see which processes are running:

1. ps (Process Status)
   • Shows current running processes.
   • Example: ps aux
     • a – shows all users’ processes
     • u – shows user/owner
     • x – includes background processes
2. top
   • Real-time monitoring of processes.
   • Shows CPU and memory usage for each process.
   • Example output columns:
     • PID – Process ID
     • USER – Owner of process
     • %CPU – CPU usage
     • %MEM – Memory usage
     • COMMAND – Name of program
3. htop (if installed)
   • Better, interactive version of top.
   • You can scroll, sort, and kill processes easily.

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3. Process States

A process can be in different states:

State	Meaning
R (Running)	Actively using CPU
S (Sleeping)	Waiting for input or a resource
T (Stopped)	Paused (manual or system signal)
Z (Zombie)	Finished but still in process table

IT example: A web server process may sleep while waiting for a request from a user.

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4. Memory Usage in Linux

Memory is where data is stored temporarily while processes are running. In Linux, memory usage is split into:

1. RAM (Random Access Memory)
   • Stores active processes and data temporarily.
   • Faster than storage drives.
2. Swap Space
   • Extra memory on disk used when RAM is full.
   • Slower than RAM.
3. Cached Memory
   • Linux keeps frequently used data in memory for faster access.
   • It’s free for processes if needed.

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5. Checking Memory Usage

Linux provides tools to see memory usage:

1. free
   • Shows RAM and swap usage.
   • Example: free -h
     • -h makes it human-readable (GB/MB)
   • Output: total used free shared buff/cache available
     8G 3G 2G 0.1G 3G 4.5G
2. top or htop
   • Also shows memory per process.
   • Useful for spotting processes using too much memory.
3. vmstat
   • Shows detailed memory, CPU, and process stats.
   • Example: vmstat 2 5
     • Updates stats every 2 seconds, 5 times.

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6. Managing Processes

Sometimes you may need to stop or restart a process:

1. kill
   • Stop a process using its PID.
   • Example: kill 1234
     • 1234 is the PID of the process.
2. killall
   • Stop all processes by name.
   • Example: killall firefox
3. nice and renice
   • Control CPU priority for processes.
   • Example: Giving a backup script lower CPU priority: nice -n 10 ./backup.sh

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7. IT Examples of Process & Memory Management

• Web server (Apache/Nginx):
  • Each request can start a new process/thread.
  • System memory must be monitored to avoid crashes.
• Database server (MySQL/PostgreSQL):
  • Heavy queries may consume a lot of RAM.
  • Swap may be used if RAM is full, slowing down performance.
• Automated backup scripts:
  • Scheduled via cron.
  • Low CPU priority using nice to avoid slowing other services.

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8. Key Exam Points

For LPI 010-160, you need to know:

1. What a process is and PID.
2. How to view processes (ps, top, htop).
3. Process states (R, S, T, Z).
4. Memory types: RAM, swap, cache.
5. Commands to check memory (free, vmstat, top).
6. How to manage processes (kill, killall, nice, renice).

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Summary Table for Quick Revision

Topic	Command / Info
View processes	ps aux, top, htop
Process ID	PID
Process states	R, S, T, Z
Memory usage	free -h, top, vmstat
Stop process	kill PID, killall name
Change CPU priority	nice, renice