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The process for managing local users and groups is straight forward and differs very little from most other GNU/Linux operating systems. Ubuntu and other Debian based distributions, encourage the use of the “adduser” package for account management.

To add a user account, use the following syntax, and follow the prompts to give the account a password and identifiable characteristics such as a full name, phone number, etc.
```
sudo adduser username
```
To delete a user account and its primary group, use the following syntax:
```
sudo deluser username
```
Deleting an account does not remove their respective home folder. It is up to you whether or not you wish to delete the folder manually or keep it according to your desired retention policies.

Remember, any user added later on with the same UID/GID as the previous owner will now have access to this folder if you have not taken the necessary precautions.

You may want to change these UID/GID values to something more appropriate, such as the root account, and perhaps even relocate the folder to avoid future conflicts:
```
sudo chown -R root:root /home/username/
sudo mkdir /home/archived_users/
sudo mv /home/username /home/archived_users/
```
To temporarily lock or unlock a user account, use the following syntax, respectively:
```
sudo passwd -l username
sudo passwd -u username
```
To add or delete a personalized group, use the following syntax, respectively:
```
sudo addgroup groupname
sudo delgroup groupname
```
To add a user to a group, use the following syntax:
```
sudo adduser username groupname
```
________________________________________________________________________________
Thanks to http://techgurulive.com/2009/01/06/how-to-add-and-delete-users-in-ubuntu/

How to Add and Delete Users in Ubuntu