echo "Hello world"

We are going to learn:

1. User / group
2. grep, awk, find.
3. File permission
4. ssh/scp
5. systemctl

• Groups: collection of users

  sudo groupadd devops
  

  use the /etc/group file to get groups

  Whenever you create a user it creates groups also with the same name.

  • Add user to group

    whenever you add a user to a group you modify the user.

    sudo usermod -aG devops user1
    

  • To add multiple users, we can also use gpasswd to add user

    sudo gpasswd -M user1,user2,user3 testers
    

  • Delete user form group

    sudo gpasswd -d user2 testers
    

  • Delete group

    sudo groupdel testers
    

  • Use chgrp to change group of file

    sudo chgrp tester file.txt
    

---

• File permissions:

  Numeric Permissions:

  • r - read = 4
  • w - write = 2
  • x - execute = 1

   

  • There are three set of permissions for:

    • U - User/Owner
    • G - Group
    • O - Others

   

  • Combinations

    _ U _ . _ G _ . _ O _ => rwx rwx rwx

    Example:

    U - read+write = 4+2 => 6

    G - read+executable = 4+1 => 5

    O - read = 4 => 4

    Final permission numeric == 654

   

  • User chmod command to modify permissions

    chmod 700 file.txt
    

 

• Find files

  • Grep: To find anything inside file or name of files.

    • Find some keyword or filename in directory.

    grep -r keyword /home/ubuntu/
    

    -r is for searching recursively inside directotries

    • grep something inside file

    grep keyword file.txt
    

    • Search case insensitive

    grep -i keyword file.txt
    

    -i stands for case insensitive, by default grep is case sensitive.

     

  • AWK:

    • Find TRACE from log and print column 1,2,5

    awk '/TRACE/ {print $1,$2,$5}' errors.log
    

    • Get the exact line number

    awk '/TRACE/ {print NR,$1,$2,$5}' errors.log
    

    • User condition using NR => row number

    awk 'NR>=1 && NR<=20 && /TRACE/ {print NR,$1,$2,$5}' errors.log
    

   

  • Find:

    • Find files with specific extension

      find *.txt
      

    • Find files in some directory with specific ending

      find dir/ *.log
      

    • Find files by a particular owner

      find dir/ -user ubuntu
      

    • Find files by a particular group

      find dir/ -group devops
      

   

• SSH:

  • Keys:

    • Public key (id_rsa.pub)

    • private key (id_rsa)

      Public key must be known by the server where you want to connect, and you must also have private key to connect.

     

  • Create keys:

    ssh-keygen
    

    Keys are stored in ~/.ssh/ directory.

  • Connect using keys:

    1. Permission must be 400

       chmod 400 key.pem
       

    2. connect

       ssh -i /path/to/key.pem user@ipaddress
       

    3. Types yes when asked.

  • scp from host system to server

    scp -i "key.pem" file.txt user@ipadd:/home/user/file.txt
    

  • scp from server to our host system

    scp -i "key.pem" user@ipadd:/home/user/file .
    

     

• Systemctl

  It is a Service controller, services like docker, apache2, sshd, nginx, etc.

  • Start any service

    sudo systemctl start <service> 
    

  • Stop any service

    sudo systemctl stop <service>
    

  • Check status of any service

    sudo systemctl status <service>