Linux Classroom Series – 14/Jul/2020

Change your password

  • Command for changing the password
passwd [user]
  • Lets login as user john and change his passwd Preview
  • Login as sudo user and change password of other user Preview
  • root user can change password of any user

Change mode

  • Syntax
chmod [reference][operator][mode] file ..
  • Reference
    • u => owner
    • g => group
    • o => others
    • a => all
  • Operators
      • => Add the modes
      • => Remove the specific modes
    • = => The modes specified are made exact
  • Examples Preview
mkdir -p modtest/{a,b,c}
ls -al modtest/
chmod g=rw modtest/a
ls -al modtest/



  • UMask is known as User Mask or it is also called as User file creation Mask.
  • This is a base permission or a default permission when a new file or folder is created in linux
touch testfile
mkdir testdir


  • The default permissions for file are 644 and for directory are 775
  • Lets add following entry into a file /etc/profile and add the entry umask 0027 Preview
  • Now observe directory permissions for the newly created directory


  • A process is basically a program that is executing.

  • Executing the program happens in a sequential

  • To run anything on OS, a process has to be created

  • For any process to run

    • A program is loaded into memory and it becomes process. Process has 4 sections
      • Stack:
        • Stack contains temporary data such as what method/function paramters, return addresses & local
      • Heap: This is dynamically allocated memory to process
      • Data: Global & static variables
      • Text: Program counter, Process registers
  • Process LifeCycle

    • Start
    • Ready
    • Running
    • Waiting
    • Terminated or Exited
  • Lets understand commands which we would examine w.r.t process

    • ps: Report the snapshot of current process
    • top: Display task
    • jobs: List active jobs
    • bg: Place the job in the background
    • fg: Place the job in the foreground
    • kill: Send a signal to a process
    • Killall: Kill a process by name
    • shutdown: Shutdown or reboot a system
  • Daemon Programs:

    • When a linux starts, kernel has to run some activites, so it initiates those activities as process and launches a program called as init
    • init runs a series of shell scripts called as init scripts, which start all the system services.
    • Many of these services are implemented as daemon programs, Programs that jus run in the background and generally they don’t have UI.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

About learningthoughtsadmin