how to check and add USER on Ubuntu

To check existing users in Ubuntu :

cut -d: -f1 /etc/passwd

To Add User in Ubuntu :

sudo adduser new_username

or:

sudo useradd new_username

To remove/delete a user, first you can use:

sudo userdel username

To delete the home directory for the deleted user account :

sudo rm -r /home/username

^{(Please use with caution the above command!)}

To modify the username of a user:

usermod -l new_username old_username

To change the password for a user:

sudo passwd username