sudo user and special permission

 deleting of user:-

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#userdel <username>   --> to delete a user without deleting his home dir

ex: #userdel maa

#userdel -r <username>  --> to delete a user with its home dir

ex: #userdel -r tokyo

creating  a sudo user:-

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-> the main purpose of creating a sudo user is to give a restricted permissions of root user to normal user

-> all the details of sudo user are stored in /etc/sudoers file

#vim /etc/sudoers

locate the line number 100 and add the entry in next line

<username> ALL=(ALL) <binary path of command>

ex: zafar ALL=(ALL) NOPASSWD:/usr/sbin/useradd

    suhaib ALL=(ALL) ALL

-> for groups if u want to give a sudo permission then go to 107 line and add the entry in next line

%<group name> ALL=(ALL) <binary path of  command>

%kxip ALL=(ALL) NOPASSWD:/usr/sbin/useradd

:wq!

--> to know the binary file path of a command is 

#which <command>  

ex: #which useradd

/usr/sbin/useradd

#su - zafar

$ useradd <username>   --> you get an error permission denied

$ sudo useradd <username>  --> to execute as a sudo user

ex: $ sudo useradd zohra

special permissions:-

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-> we have 3 special permissions in linux OS:

1) SUID  (set user ID)

2) SGID (set group ID)

3) sticky bit 

SUID:-

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-> it is used to assign root user permmission to all normal users

-> if as a normal user we give root user commands it error as permission denied

-> apply SUID permission for perticular commands binary file

-> numerical value of SUID is "2"

to apply:-

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#which <command>   -> to know the binary file path of command

ex: #which useradd

/usr/sbin/useradd

#chmod u+s  <binary file path>

ex: #chmod u+s  /usr/sbin/useradd

#su - red

$useradd papa

#chmod u-s <binary file path>   --> removing a SUID permission on a perticular commands binary file

ex: #chmod u-s /usr/sbin/useradd