Keep in mind that only basic commands are presented here. NO details or particulars! Use official manuals and guides to get a deeper understanding.
Q: How to install an application?
A1: In FreeBSD go to cd /usr/ports/ find the app, get into the app’s folder and issue the command make install clean.
A2: In CentOS just use yum install [package name] command.
A3: In Ubuntu type apt-get install [package name].
Q: How to scroll text ?
A: In FreeBSD use ScrollLock button. In CentOS hold down Shift and use Page Up or Page Down keys.
Q: How to bring a process back to foreground?
A: Issue jobs command. Find the application, look at at the number accociated with it and use fg [number] command to fetch it.
Q: How to stop a process?
A: You must see the list of all processes first by issuing top command. Find the one you need to stop and issue killall -9 [name of process]. This will kill any process with that name.
Q: How to shut down a firewall in CentOS / Red Hat?
A: Issue service iptables stop command.
Q: How to automatically start a service at boot up procedure in CentOS / Red Hat?
A: Issue chkconfig [service name] on. E.g. to enable the httpd service in four runlevels, type chkconfig httpd on.
Q: How to find a package by a keyword?
A1: In Ubuntu type apt-cache search [key word] or proceed to http://packages.ubuntu.com/.
A2: In CentOS type yum provides ‘*/[key word]’.