======Users and Groups======
=====Create User=====
<code>useradd -g USERS_MAIN_GROUP -G SECONDARY_GROUP1,SECONDARY_GROUP2 -m -d /home/USERNAME USERNAME</code>
=====Create Group=====
<code>groupadd GROUPNAME</code>
=====Add Secondary Group to User=====
<code>usermod -a -G GROUPNAME USERNAME</code>
=====Change Password=====
Run as root
<code>passwd USERNAME</code>
Or run as yourself to change your own password
<code>passwd</code>
Change password without interaction (e.g. withing a script)
<code>echo "username:new_password" | chpasswd</code>
=====Lock Password=====
<code>passwd -l USERNAME</code>
=====Unlock Password=====
<code>passwd -u USERNAME</code>
=====Delete Password=====
Preferred way of doing it as you don't even get the option of trying to log in.
<code>passwd -d USERNAME</code>

=====See User Limits=====
Display max number of processes, etc for a particular user.
<code>ulimit -a USERNAME</code>
=====Set User Limits=====
Set max number of processes for a user for just that session
<code>ulimit -Su USERNAME</code>