To list all users you can use:

cut -d: -f1 /etc/passwd

To add a new user you can use:

sudo adduser new_username

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

sudo userdel username

Then you may want 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

To change the shell for a user:

sudo chsh username

To change the details for a user (for example real name):

sudo chfn username

$ whoamiuser1$ su - user2Password:$ whoamiuser2$ exitlogout

Ubuntu user switch