Operation Manual

adjust this setting in Chapter 6, “Configuring the Raspberry Pi”.
When you use the HDMI output, the display type is usually automatically detected. If you’re using an HDMI to DVI adapter to
plug the Pi into a computer monitor, however, this occasionally goes awry. Common symptoms include snow-like static, missing
picture portions or no display at all. To fix this, note the resolution and refresh rate of your connected display, and then jump to
Chapter 6 to find out how to set these manually.
Another issue is a too-large or too-small image, either missing portions at the edge of the screen or sitting in the middle of a large
black border. This is caused by a setting known as overscan, which is used when the Pi is connected to TVs to avoid printing to
portions of the display which may be hidden under a bezel. As with other display-related settings, you will learn how to adjust—
or even completely disable—overscan in Chapter 6.
Boot Diagnostics
The most common cause for a Pi to fail to boot is a problem with the SD card. Unlike a desktop or laptop computer, the Pi
relies on files stored on the SD card for everything. If Pi can’t talk to the card, it won’t display anything on the screen or show
any signs of life at all.
If your Pi’s power light glows when you connect the micro-USB power supply, but nothing else happens and the OK light
remains dark, you have an SD card problem. First, ensure that the card works when you connect it to a PC, and that it shows
the partitions and files expected of a well-flashed card. (For more details, see Chapter 2, “Linux System Administration”,
particularly the section titled “File System Layout” in that chapter.)
If the card works on a PC but not in the Pi, it may be a compatibility problem. Some SD cards—especially high-speed cards
marked as Class 10 on their labelling—don’t operate correctly when connected to the Pi’s onboard SD card reader. A list of
cards known to cause compatibility problems with the Pi can be found on the eLinux wiki:
http://elinux.org/RPi_VerifiedPeripherals#Problem_SD_Cards
Sadly, if you have one of the cards on the list, you may need to replace it with a different card in order for the Pi to work. As the
Pi’s software base is developed, however, work is being carried out to ensure that a wider range of cards operate correctly with
the Pi. Before giving up on a high-speed card completely, check to see if an updated version of your chosen Linux distribution is
available. (See Chapter 1, “Meet the Raspberry Pi”, for more information about distributions.)
Network Diagnostics
The most useful tool for diagnosing network problems is ifconfig. If you’re using a wireless network connection, jump to
Chapter 4, “Network Configuration”, for information on a similar tool for those devices. Otherwise, read on.
Designed to provide information on connected network ports, ifconfig is a powerful tool for controlling and configuring the
Pi’s network ports. For its most basic usage, simply type the tool’s name in the terminal:
ifconfig
Called in this manner, ifconfig provides information on all the network ports it can find (see Figure 3-2). For the standard
Raspberry Pi Model B, there are two ports: the physical Ethernet port on the right side of the board, and a virtual loopback
interface that allows programs on the Pi to talk to each other.
Figure 3-2: The output of ifconfig on a Raspberry Pi Model B