groupadd group_name create a new group

groupdel group_name delete a group

groupmod -n new_group_name old_group_name rename a group

useradd -c "Nome Cognome" -g admin -d /home/user1 -s /bin/bash user1 create a new user belongs "admin" group

useradd user1 create a new user

userdel -r user1 delete a user ( '-r' eliminates home directory)

usermod -c "User FTP" -g system -d /ftp/user1 -s /bin/nologin

user1 change user attributes

passwd change password

passwd user1 change a user password (only by root)

chage -E 2005-12-31 user1 set deadline for user password

pwck check correct syntax and file format of '/etc/passwd' and users existence

grpck check correct syntax and file format of '/etc/group' and groups existence

newgrp group_name log in to a new group to change default group of newly created files