3 free and easily available tools for usability testing

Problem Steps Recorder
Windows 7 comes pre-installed with "Problem Steps Recorder".
Go to "Start", search for "Problem Steps Recorder". Under settings, remember to set the number of steps as 100.

TeamViewer
Allow remote access.

InvisionApp
More for designers, but you can upload a screenshot and let your clients comment on the mockup.

Better than screenshots or emails, saves a lot of frustration.

Linux server admin - Adding user accounts, resetting passwords

When logged in as your own account and changing your own password:

$ passwd

As superuser (or root), changing the password for other accounts

Find out list of users

$ cat /etc/passwd | cut -d: -f1

Change password for account "guest1"

$ passwd guest1

Add users (with default configuration)
$ useradd guest1
(http://www.thegeekstuff.com/2009/06/useradd-adduser-newuser-how-to-create-linux-users/)