User management

Syntax

useradd -m -s /bin/bash UserX           #Creates user, -m gives home directory and -s gives default shell
passwd UserX                            #Gives password to a user  ?To not give it by insecure plaintext, we first create the user, then use the passwd command on the new user
chage -M n UserX                        #Makes the password expire in n days for UserX
chage -l UserX                          #Shows password caducity configuration
chage -d 0 UserX                        #Forces to change password in next login
chage -m n UserX                        #Configures n days before user can change password again
adduser UserX                           #Creates user but step by step, easier
id UserX                                #Prints user ID and GID (Group ID)
su UserY                                #Changes user
deluser --remove-home UserX             #Removes user and files in home directory
userdel -r UserX                        #Removes user and files in home directory
cat /etc/group                          #File with all groups and its users in the system
getent group GroupX                     #Shows users in a group
getent group sudo                       #Check users with sudo privileges
usermod -aG GroupX UserX                #Adds user to a group
sudo usermod -aG sudo UserX             #Give sudo privileges to a user
gpasswd -d UserX GroupX                 #Removes user from group
usermod -G GroupY,GroupZ UserX          #Overwrites user to specified groups and removes it from others not listed  ?For example if he was on GroupX he would be removed and added to GroupY and GroupZ

Configure password policies

Using sudowill ignore all policies

#libpam-pwquality configuration file
sudo nano /etc/security/pwquality.conf         #Configuration file for pass polcies
minlen = n                                     #Minimum lenght for new passwords
ucredit = -n                                   #Minimum upper characters  ?ucredit = -2 would mean at least 2
dcreit = -n                                    #Minimum digits 
ocredit = -n                                   #Minimum others/symbols
badwords = P@ssword Passw0rd iloveyou          #Prohibits specified passwords
remember = n                                   #Prohibits using N last passwords used