SAM-PREFINAL

Process Characteristics

  • Initiated from GUI or command line.

  • Can spawn new processes.

  • Created only by other processes.

Commands for Viewing and Controlling Processes

  • ps: Displays a snapshot of current processes.

  • top: Shows current active tasks.

  • jobs: Lists active jobs.

  • bg: Sends a job to the background.

  • fg: Brings a job to the foreground.

Process States in ps Command

State

Meaning

R

Running

S

Sleeping (awaiting an event)

D

Uninterruptible sleep (awaiting I/O)

T

Traced or stopped

Z

Zombie (terminated but not cleaned up)

Additional Indicators with Process States

  • <: High priority.

  • N: Low priority.

  • L: Locked in memory (real-time I/O).

  • s: Session leader.

  • l: Multi-threaded.

  • +: In foreground group.

ps Command with aux Option Headers

Header

Meaning

USER

Owner of the process

%CPU

CPU usage percentage

%MEM

Memory usage percentage

VSZ

Virtual memory size

RSS

Resident set size (physical memory used)

START

Process start time

top Program Overview

  • System Summary: Shows time up and load average (last 1, 5, and 15 minutes).

  • Tasks Summary: Number of processes and states.

  • CPU Activities: Includes user, system, and idle %.

Columns in top Program

Header

Meaning

PID

Process ID

USER

Username

PR

Priority (ranges from -20 to 19)

NI

Niceness value

VIRT

Total virtual memory used

RES

Resident size in KB

SHR

Shared memory size

S

Process status

%CPU

CPU usage at last update

%MEM

Memory usage at last update

TIME+

Cumulative CPU time used

COMMAND

Name or path of process

Controlling Processes

  • Interrupt a process: Ctrl + C.

  • Background a process: Use bg or jobs.

  • Return a process to foreground: Use fg.

Networking Basics

  • Computer Network: A system connecting computers to share resources.

  • Requires:

    • Network interface (e.g., Ethernet device).

    • Running network services.

    • Access to a network broadcast device (hub, switch, router, gateway).

TCP/IP Layers

  1. Network Interface Layer: Handles packet placement and reception.

  2. Internet Layer: Addresses, packages, and routes packets (includes IP, ARP, ICMP, IGMP).

  3. Transport Layer: Provides communication services (includes TCP, UDP).

  4. Application Layer: Deals with data exchange protocols (e.g., HTTP, FTP, SMTP, Telnet).

Networking Protocols

  • DNS: Resolves hostnames to IP addresses.

  • RIP: Exchanges routing info between routers.

  • SNMP: Manages network devices.

Common Networking Commands

  • ping: Sends ICMP ECHO_REQUEST to hosts.

  • traceroute/tracepath: Traces packet routes to hosts.

  • ip: Manages routing and devices.

  • netstat: Displays network connections and statistics.

  • ftp: File transfer program.

  • wget: Downloads files non-interactively.

  • ssh: Remote login program (OpenSSH).