All the below operation use /etc/login.defs configuration file for creating user, home dir and other, It’s part of shadow password suite.

• Add user to system : useradd user_name
• Create user without home-directory : useradd -M user-name
• Create user but not create group with same user-name: useradd -N user_name
  • It will not create group with same as user-name while creting new user.
• Create user with specific shell on login : useradd -s /bin/bash user-name
• Create user with specific user-id and group-id : useradd -u 123 -g 133 user-name
  • -u for user-id.
  • -g for group-id.
• Create user with specific shell, specific home directory, some comments, specific user-id
• useradd -m -d /var/www/home-dir -s /usr/sbin/nologin -c "first last" -u 1019 avishek
  • -c : Sort description of the login, usually used to write user’s full name.
  • -m : Create home-dir if doesn’t exist.
  • -d : Home directory path
• Add user to multiple groups: useradd -G group1,group2 user-name
• List the groups user is added to :
  • groups username or

  • cat /etc/groups

    grep username

• List all the members of group :
  • members groupsname or

  • cat /etc/groups

    grep groupname

Reference:

• https://superuser.com
• https://www.tecmint.com
• http://www.binarytides.com/linux-find-command-examples/