How to compress an entire directory on GNU/Linux tar

tar -cvf filename.tar.gz directory_to_compress/

How to mount ISO image into GNU/Linux filesystem

You must be logged as a root and execute the following command, assuming that you have a mount point directory (/mnt/disk1) already created.

mount -o loop disk1.iso /mnt/disk

Source: http://www.cyberciti.biz/tips/how-to-mount-iso-image-under-linux.html

Enable PAE support for the CentOS virtual image, on VirtualBox

When trying to dun a CentOS image in my VirtualBox, I got the following error.

This kernel requires the following features not present on the CPU:
PAE
Unable to boot - please use a kernel appropiate for your CPU.

Due to the new kernel version of CenOS 6, we are required to have PAE support enabled in the actual virtual machine. To proceed with this we just need to run the following console command, which sets to On mode PAE support for the current machine.

VBoxManage modifyvm SlackVM2 --pae on

Info taken from: http://slackblogs.blogspot.cz/2011/06/pae-support-on-virtualbox.html