How to reinstall OS X Mavericks without losing your data

If you're a little too geeky like me and you mess up too much with your OS X (installs, uninstalls, kernel extensions, etc.) you may need to refresh it, but what if you don't have the time or the disk space needed for a backup?

Not everybody knows that you can re-install OS X without losing your data.

NOTE: This is an extreme situation and you may want to backup your disk or, if you already have previous backups, at least copy elsewhere the files changed or created since the last backup, for you to make sure you don't lose them.

The above warning is a little paranoid, but I've learned you'd better be like that in I.T., because you never can tell (every time you say: "No, this is not gonna happen!", rest assured it will).

What you need

1. OS X Mavericks installer: You can download it from App Store (good luck and see you in some hours!) or use a copy you already have. I chose the second option because App Store servers are always very slow. If you have time and patience, you might want to download the latest version right away, so you won't have to update the system after the installation, but it's your call.
2. Some time: It takes a while, so be prepared. Grab a book or a tall coffee mug.

How to do it

1. Double-click Install OS X Mavericks.app:  This will launch the setup wizard and will allow you to overwrite your OS X. Very important: DO NOT DELETE YOUR CURRENT PARTITION. In this case, you don't want a clean install, but a simple re-installation to solve system issues. 
2. Launch App Store and check Updates: After successfully reinstalling OS X Mavericks, check App Store to make sure you have its latest version. If you've used an outdated Mavericks installer, you might have to install an OS X Update Combined for you to upgrade to its current version  (in my case, I had to upgrade back from OS X 10.9.2 to 10.9.4 after re-installing Mavericks). This step might not be needed if you've chosen to download the latest version of Mavericks Installer in the step 1. 

Final result

That's it! I've only had to re-install Caffeine because it wouldn't work for some unknown reason, but all the rest looks good and I got my operating system as brand new, without losing my files or my apps.

Wrap-up

If your OS X is experiencing issues and you want to solve them quickly, without losing your files and applications, you can re-install your OS without formatting your hard drive.

You should always backup your files before doing it; in my case I didn't perform any backup because of time and disk space constraints, but I didn't lose any data because this operation simply overwrites the system files, leaving all the rest untouched.

You only need to download and run Install OS X Mavericks.app from App Store (or double-click it only, if you already have a copy of the installer).

In the latter case, you want to check for updates after reinstalling OS X, to make sure you have its current version.