What is a Sea level? Are we at Sea level at Sea?

Sea level is a measure of the average height of the ocean's surface (such as the halfway point between the mean high tide and the mean low tide); used as a standard in reckoning land elevation.


Gravity is stronger in different places on Earth's surface, so sea level may be higher or lower depending on the strength of gravity.   Source

Funny one liners over the internet!

1. I downloaded winrar once but it came in a .rar

How Does Wi-Fi Work on Airplanes?

I have always come up with question in my head which I didn't have time to google. From, now on I am planning to google all those queries and put it here. Ok back to the question:

How Does Wi-Fi Work on Airplanes?

Source:

Transmitters on the plane communicate with a ground station, either using radio waves similar to a cellphone or through a satellite link, depending on the provider.

Satellite Communications
In a satellite communications system, a satellite antenna on top of the plane communicates with a satellite in orbit above the earth. The satellite also communicates with a ground earth station, which has a direct connection to the Internet. When a passenger requests a Web page on her laptop from the plane's Wi-Fi access point, the plane's electronics transmit the request to the satellite, which then relays it to the ground station. The ground station then transmits the requested page to the satellite, which in turn relays the data to the plane. The wireless access point then sends the data to the passenger’s laptop. Although the signals travel large distances, speeds of up to 11Mbps are currently available.


Ground-Based Cellular Networks
In a ground-based system, an antenna located on the bottom of the plane transmits and receives signals to and from ground-based towers and works in a similar way to mobile phone networks. The plane's antenna transmits signals to the nearest tower, which in turn relays the signals to a ground station. The ground station retrieves the necessary data, which the cell tower broadcasts to the plane. As providers erect more towers, the area covered by the network expands. For faster expansion, existing cellphone towers can be fitted with the necessary equipment. Due to FCC regulations, the network is not available below 10,000 feet as the license is only for aeronautical use.

Restrictions
To avoid disturbing other passengers, the systems automatically drop any packets containing voice data, while passing other data through. Due to the need to be in contact with a tower, ground-based systems do not work on international flights or over large bodies of water, and the service may slow down if a number of people on board the flight use the connection.

How to delete a UNIX directory with a hyphen in the name

rm -rf -- -directoryName
The -- after rm tells it to stop looking for options.

Alternatively, you can put "./" in front of directory name
rm -rd ./-directoryName