R-Pi Troubleshooting

From eLinux.org
Jump to: navigation, search

Back to the Hub.

This page lists the most common problems and suggests some solutions.

See RPi_Bugs for problems that are bugs.


Power / Start-up

Note: if you have any kind of booting problems, start off by reading the "Is your Pi not booting? (The Boot Problems Sticky)" in the troubleshooting section of the Official Raspberry PI forum [1].

A good power supply that will supply 5 volts and at least 1 amp (5V 1A) is vital. A 5 volt 2 amp power supply can help some wifi USB adapters run more stable. For more information see #Troubleshooting_power_problems.

Note that the Pi has no BIOS, so nothing will be displayed on screen unless the Pi successfully boots!

Normal LED status

There are five LEDS near the USB connector.

LED statuses
LED colour function normal status
ACT green card status flashing during SD card activity
PWR red power steady ON when Pi receives some power on original B and A, but since the B+ (except for the zero) the PWR LED is also a power good indicator that goes off when power drops below 4.65V
FDX orange full duplex on when Ethernet connection is full duplex
LNK orange link on when Ethernet is connected
100 orange 100 Mbps on when connection is 100 Mbps off when 10 Mbps

See the next sections for how to interpret other statuses.

Red power LED does not light, nothing on display

The power is not properly connected.

Red power LED is blinking

A blinking red power LED indicates problems with the power supply. On model A and B, it is hard-wired to the 3.3V power supply rail. If it is blinking, as one user has reported[1] it means the 5V power supply is dropping out. Use a different power supply.

On model B+ (and presumably also the A+), the circuit has been improved to give a much more reliable warning of poor power quality. The red power LED is wired to an APX803 supervisor[2] which kicks in when the 5V power supply drops below 4.63V[3]. If it does, the LED will blink. Check your connections, cable, and power supply.

Red power LED is on, green LED does not flash, nothing on display

Start off by reading the "Is your Pi not booting? (The Boot Problems Sticky)" in the troubleshooting section of the Official Raspberry PI forum [2] it contains the latest info about "Red power LED is on, green LED does not flash" kind of problems. Note: A faintly glowing steady green LED means no boot code has ever been executed, as almost the first thing the boot code does is to turn the faint glow off! When flashing/blinking the green LED should be as bright as the red LED.

Note also there is a difference between the quad core Pi 2 (BCM2836) and the other models if there is no SD card inserted, or the SD card is improperly formatted. The former will have both red and green lights on bright and steady. The latter will have only the red light on. This indicates:

  • The Raspberry Pi cannot find a valid image on the SD card. Turn the board over to check that the card is inserted correctly; the insertion force is much larger than for some laptops.
    • Check that you have correctly written a Raspberry Pi image to the card by using a MAC or PC and browse for the following files:
      • bootcode.bin
      • fixup.dat
      • start.elf amongst others
    • Did you have admin rights when you used the SD-card writer software? Without it the software might go through the motions without actually doing anything!
    • Older images do not load boot code for revB boards with the Hynix chip. Use release 2013-02-09 (?) or later. (I observe a single blip on the green activity LED)
    • It is also possible that the image you are writing to the card is corrupt, as downloads do occasionally end up corrupted or truncated. You can check with a checksum utility to verify the integrity of the download.
  • Try with no cables connected except the USB power lead, and SD card inserted. You should see flashing of the OK light for ~20 seconds. If that helps, plug in cables one at a time to identify which is interfering with boot.
  • Confirm the USB cable is properly seated in the power slot. The red power LED does not necessarily mean it is fully connected.
  • Look at the SD card holder on the Raspberry Pi carefully. At first glance it may look fine but the contacts must be springy and they must protrude at least 2mm as measured from the lower edge of the holder to the top of the contact bulge. This happens due to the solder process and the type of holder used. Some of the solder residue falls into the contact cavity restricting the springiness and the height that the contact protrudes. You can fix this yourself but remember you can void your warranty. The contacts are delicate so be carefull. Insert a needle pin under the contact bulge and pull lightly up until the one end of the contact unclips. Clean the cavity where the contact unclipped from of any solder or other residue by blowing into the cavity. Clip the contact back into the cavity by lightly pushing it into the cavity. Do this for all the contacts. Look at these photos. Media:SDcardHolder.JPG, Media:UnclipContact.JPG, Media:UnclippedContact.JPG
    • Ensure that when your SD Card is fully inserted that the longer metal spring contacts (one clearly visible on the end of the slot, and one hidden in the side nearest the power connector) are closed. These are used to detect the presence of an SD Card therefore if no contact is made then the Raspberry Pi won't attempt to access the the card.
    • Check carefully for any cracks or damage to the SD Card slot, if the sides are damaged then the card may not be making proper contact with the pins (can usually confirm this if your Raspberry Pi boots if you manually hold the SD Card in position). For ways to resolve this, see PiHardware - SD Card slot fixes for more info.
  • The voltage is too low (below 5 V), try a different power supply and/or cable. The R-Pi needs a supply rated for 700 mA or more. Some supplies labeled as such cannot actually provide their rated current while maintaining 5V. See also, #Troubleshooting_power_problems.
  • (unlikely) hardware abuse, for example by connecting a 7 V supply to a 3v3 GPIO output pin[4] or powering up the board after a solder splash shorts some traces[5].
  • If for whatever reason the main polyfuse F3 has been overheated previously it may happen that it hasn't completely recovered, in which case, if you turn the PI on, a considerable amount of energy from the power supply is lost in the fuse and doesn't reach the PI. Try if the polyfuse seems hot. For this problem too read #Troubleshooting_power_problems.
  • Some problems have been reported if the ambient temperature is low that might be related to micro-fractures, fissures in solder or other issues. Try warming the Raspberry Pi with a hair dryer for just a few seconds (do not use excessive heat or you may cause irreversible damage!) and reconnect the power. Check this video http://www.youtube.com/watch?v=AwF6v-4NFdg

Green LED blinks in a specific pattern

  • 1 flash: possibly you have a Rpi from Micron. Take a good look at the processor if it says M with an orbit around it. Using the lastest software ( >= sept 2013 ) will solve your problem. And make sure you have a 4Gb SD card: a 2Gb doesn't work.
  • 2 flashes: The SD Card cannot be read.

Solution : Format card and flash Raspbian with Pi Installer from Terminal.

- SD Formatter (Mac + Win) https://www.sdcard.org/downloads/formatter_4/eula_mac/index.html

- Pi SD Installer by RayViljoen: https://github.com/RayViljoen/Raspberry-PI-SD-Installer-OS-X

According to this forum post the green light will blink in a specific pattern to indicate some types of errors:

  • 3 flashes: loader.bin not found
  • 4 flashes: loader.bin not launched
  • 5 flashes: start.elf not found
  • 6 flashes: start.elf not launched
  • 7 flashes: kernel.img not found

Firmware since 20th October 2012 no longer requires loader.bin, and the flashes mean:

  • 3 flashes: start.elf not found
  • 4 flashes: start.elf not launched
  • 7 flashes: kernel.img not found
  • 8 flashes: SDRAM not recognised. You need newer bootcode.bin/start.elf firmware.

If start.elf won't launch, it may be corrupt.

Note that 4-flashes may point to a defective SD-card holder, if one or more of the data contacts is intermittent it can lead to this problem.

Coloured splash screen


With current firmware, a coloured splash screen (actually its just four pixels "blown up" by the GPU to full screen) is displayed after GPU firmware (start.elf) is loaded. This should be replaced by linux console a second later. However if the coloured screen remains, it suggests the kernel.img file is failing to boot. Try replacing it with a known good one.

Immediately after displaying the splash screen, the PI starts consuming a little more current. If the PI resets at that moment, it is an indication that the power supply isn't able to deliver the full current your PI requires, but dips its output voltage below a minimum when loaded with the full current the PI needs.

In some cases (Stuck on the Rainbow Screen), freezing at this point has been fixed by adding "boot_delay=1" to the config.txt file. This can be done from a Windows PC, which should show several files in the FAT partition on your SD card including bootcode.bin, kernel.img, and config.txt. You can open config.txt in wordpad or any text editor. Add "boot_delay=1" and save the file. Don't forget to 'eject' the card before removing it from the reader. If you are reading the SD card from a working Pi, you can edit the file with sudo nano /boot/config.txt

Kernel Panic on boot

Text appears on screen, but then hangs with debug messages. This can be caused by USB devices such as keyboards. Try again with nothing in the USB.

Raspberry Pi shuts down (or restarts) soon after booting up

This is caused by a power supply producing too low a voltage. See #Troubleshooting_power_problems.

Pi boots sometimes but not always

With a known good power supply and known good SD card, the R-Pi boots occasionally, but other times shows only a tiny green flicker from the "OK" LED and it fails to start, even with no USB devices and no Ethernet. This has been reported several times[6] [7] [8] and remains an open issue. Low voltage or an improper SD card can cause it. Some SD cards will work until they warm up slightly, and then fail[9]. When exposed to 21 C room temperature the warmest part of an uncased working R-Pi should be 41 C[10]. The wiki has a list of working SD cards. Buy from a reliable vendor as it has been claimed that 1/3 of all "Sandisk" labelled memory cards are counterfeit.

  • It could be that the SD memory card is not making proper contact with the Raspberry Pi. Look at the SD card holder on the Raspberry Pi carefully. At first glance it may look fine, but the contacts must be springy and they must protrude at least 2mm as measured from the lower edge of the holder to the top of the contact bulge. Variations happen due to the solder process and the type of holder used. Some of the solder residue falls into the contact cavity, restricting the springiness and the height that the contact protrudes. You can fix this yourself, but remember you can void your warranty. The contacts are delicate, so be careful. Insert a needle pin under the contact bulge and pull lightly up until the one end of the contact unclips. Clean the cavity where the contact unclipped from any solder or other residue by blowing into the cavity. Clip the contact back into the cavity by lightly pushing it into the cavity. Do this for all the contacts. Refer to these photos: Media:SDcardHolder.JPG, Media:UnclipContact.JPG, Media:UnclippedContact.JPG

Keyboard / Mouse / Input Devices / Webcams

R-Pi does not respond to key presses / Keyboard randomly repeats key presses

note:during entering the password most linux distro's wont show that you typed in anything (not even "*" characters) this is normal behaviour, try the keyboard while entering the user name!

This is most often caused by inadequate power. Use a good power supply and a good power cable. Some cheap cables that work with a cell phone, cannot fully power the R-Pi. Some USB devices require a lot of power: most will have a label showing the voltage and mA requirements. They should be 5v 100mA each max, any more than this they must be used with a powered USB hub. Try unplugging every USB device except the keyboard (you should also note that some keyboards have built in hubs and can try to draw 150mA (Pi can only handle 100mA per USB slot without a hub)). Also, use the latest software. Forum user MrEngman reported some keyboard repeats and wireless hangs until upgrading to the debian6-19-04-2012 kernel, which he reports stable with no problems even with a low TP1-TP2 voltage of 4.65 - 4.68 volts.

Some users have reported that their keyboards work fine on Arch linux, but on Debian distro's, their keyboards become erratic (repeats and/or skips key presses). One suggested remedy to this, which has some positive feedback, is to adjust the USB bus speed. To do this, you need to edit the cmdline.txt file, and add "dwc_otg.speed=1" (without quotes) to the end of the file (found in the /boot directory).

Worst case scenario, some (advanced) keyboards, such as the Roccat Arvo, have kernel modules that need activating. If you have access to another keyboard temporarily, you will need to modprobe the relevent driver. Or if this is not possible, you can rebuild the kernel (instructions available on the wiki page) with the modules installed. (to find the drivers for keyboards etc, you need to find "Device Drivers -> hid Devices".)

As a workaround you can use programs kbdrate and xset to tune the keyboard repeat rate:

kbdrate -r 2.0 -d 1000

on the console and

xset -r

on the desktop (xset is available with: sudo apt-get install x11-xserver-utils)

Sticky keys

Many wireless keyboards are known to have "sticky keys" on the R-Pi. Work has recently (summer 2013) been done on the USB code. Updating to a recent firmware might help. Updating the firmware can be done with rpi-update. Recent Raspbian releases comes with rpi-update installed.

sudo rpi-update

Note that the firware sits on the SD card, so each card, not R-Pi has to be updated.

Keyboard / Mouse interferes with USB WiFi device

Connecting a keyboard and/or mouse while a USB WiFi device is connected, may cause one or both devices to malfunction. On April 30 2012, there was a bugfix[11] relating to USB sharing between high-speed (eg. WiFi) and full/low-speed devices (eg. keyboard/mouse). User spennig[12][13] reports this patch did not fix the Mouse/WiFi conflict. On 2012-05-12, user spennig was pleased to confirm that wifi was working with a USB keyboard and mouse, as long as the Raspberry Pi had a good PSU and a powered hub. Even so, some experimentation was needed, e.g. USB WiFi connected to the device, and the keyboard and mouse connected to the powered hub. Some experimentation may be necessary to find a working combination; however a good power supply is essential.

My experience regarding this issue point to interferences in the 2.4 GHz frequency band in which both WiFi sticks, as well as USB keyboards transmit data. Changing the channel on the wireless access point fixed the problem completely. In my case (Belkin N150 + Logitech K260/M210) I switched from channel 1 to channel 13, which results in a frequency shift of 50 MHz. Possibly enough to not affect the keyboard/mouse receiver.

Wireless Keyboard trouble

Some wireless keyboards, for example the Microsoft Wireless Keyboard 800 are reported to fail[14] even though the current drawn by the wireless adaptor is within the R-Pi USB spec limit of 100 mA. This may be a software driver problem.

Re-mapping the keyboard with Debian Squeeze

If different letters appear on-screen from that which you typed, you need to reconfigure you keyboard settings. In Debian, from a command line type:

sudo dpkg-reconfigure keyboard-configuration

Follow the prompts. Then restart your RasPi.
From the command line type:

sudo nano /etc/default/keyboard

Then find where it says


and change the gb to the two letter code for your country. [3]

Slow keyboard mapping

If you have remapped your keyboard and get a very long delay during the keyboard mapping at startup, type the following once on the command line after you have logged in:

sudo setupcon

No USB device works, with known good PS, SD card, KB

There has been more than one report[15][16][17] of a R-Pi booting but not getting USB input, using a known-good power supply, SD card, and keyboard. The more common cause for no USB devices working is low power supply voltage from bad PSU, cable, or USB hub, but in this case the problem was no clock signal present at the LAN9512 USB/Ethernet chip "IC3", and the solution was to reflow the solder on the 25 MHz crystal "X1" on the bottom side of the board. Or return the board for a replacement, but before making this conclusion, confirm known good peripherals. A significant number of USB keyboards are not compatible with R-Pi. As of June 1 2012, Eben reported[18] that only about 1 in 1000 shipped R-Pi boards have been found to have a hardware fault of any kind.



sudo apt-get install guvcview

Use the excellent guvcview program to test your webcam and to change the capture settings. You can improve the frame rate to a great extent by changing the settings.

hub or internal usb

It is possible that your camera will only work on an internal usb port and not on the hub.


If you are experiencing freezes or timeout errors while using a webcam this script may help:

sudo rmmod uvcvideo
sudo modprobe uvcvideo nodrop=1 timeout=5000 quirks=0x80

(quirks=0x80 is a bandwidth quirk, the necessary bandwidth will be estimated by the uvcvideo driver instead of using the one proposed by the camera)

Updating firmware

Check your firmware version

Using the latest firmware version may help various problems with SD card and display compatibility. Check the kernel version with:

 uname -a
   Linux RPi 3.1.19 #1 PREEMPT Fri Jun 1 14:16:38 CEST 2012 armv6l GNU/Linux

And the GPU firmware with:

 /opt/vc/bin/vcgencmd version
   May 31 2012 13:35:03
   Copyright (c) 2012 Broadcom
   version 317494 (release)

Get the latest firmware version

The GPU firmware and kernel can be updated with Hexxeh's rpi-update tool.

However this requires the Pi to be successfully booted. With sdcard problems, you may not get that far, so can try a manual udpate. If you have a Linux machine, rpi-update can be run on that in an offline mode. Use this to download rpi-update:

curl -L --output rpi-update https://raw.githubusercontent.com/Hexxeh/rpi-update/master/rpi-update && sudo chmod +x rpi-update

and this to run it:


Make sure to substitute in the paths to the root and BOOT partitions on your SD card (likely something like /media/USER/root and /media/USER/BOOT), or it will install it on your linux machine! If you do this by accident, wait until the tool finishes, then delete /boot and move /boot.bak to /boot

Otherwise, on a Windows computer, you will see the "/boot" partition appear as the contents of SD card. You can download the latest GPU firmware version here. Click on view raw, then save it, and put the new start.elf file on the sdcard replacing the existing one. Similarly, the latest kernel is here. After updating these files you should be able to boot. You still need to run rpi-update to update the kernel modules (in /lib/modules) and the GPU libraries (in /opt/vc).

If you are still having issues after update, you could also try the bleeding edge firmware by using the BRANCH=next option in rpi-update. If you are seeing SD card corruption after updating follow the SD Card/Power supply investigation steps. Firmware updates can be I/O intensive and reveal other issues.

Choosing the right ARM/GPU memory split

There is a choice of how the 256M/512M of RAM is divided between the ARM and GPU:

   gpu_mem=16 :  16M GPU,  240M/496M ARM split : Maximum ARM memory. Good for ARM desktop use. No accelerated video or 3D possible.
   gpu_mem=64 :  64M GPU,  192M/448M ARM split : Reasonable ARM memory. Simple video (omxplayer) or 3D (quake) is possible. This is the default.
   gpu_mem=128 : 128M GPU, 128M/384M ARM split : Use this for heavy 3D work, or 3D plus video. Needed for XBMC.

To switch, edit the gpu_mem= setting in your config.txt and reboot.

Note: other amounts are also possible, but setting gpu_mem=32 is usually the wrong choice. gpu_mem=16 is almost always a better choice.

Also note that before the release of the 51MB PI a different method was used based on splitting the 256MB RAM in a part for the CPU and GPU. As this noting system was causing trouble if the amount of RAM was not always the same. the above new method was adapted.

Make sure your editor doesn't change the first letter of the line into an uppercase letter, as some editors do. The entry is case sensitive.

SD cards

  • If you have problems, check you have latest firmware version (described above)
  • Some SD cards do not work on the R-Pi, so check the list of known SD cards.
  • If you are having problems setting up your SD card you might want to start by erasing it completely - especially if it has been used elsewhere and still contains data / partitions.
  • Reformatting cards is also easy to do in a digital camera.
  • After writing the image to the SD card, verify that you can see the boot partition when you insert the SD card into your computer. The partition should contain a number of files, including start.elf and kernel.img. If you do not see these files on the SD card, you have made an error writing the image file.
  • If you are manually preparing your SD card on Linux or Mac OS using the dd command, this operation will completely erase any existing data and partitions. Make sure you write to the whole card (e.g. /dev/sdd) and not to an existing partition (e.g. /dev/sdd1).
  • If you have an sdcard that doesn't work with latest firmware, head over here.
  • If you put the SD card into your PC in an attempt to write the R-Pi operating system onto it, and the PC tells you the card is write-protected, even with the write-protect tab in the correct, forward position, then you may have a faulty SD-card rewriter. There's a common fault with many SD-card rewriters - The write-protect tab is detected by a very thin, narrow metal strip, that is part of a switch. When the card is inserted, the write-protect tab is supposed to push the strip and make/break the contact, as needed. Unfortunately, these strips have a habit of getting stuck, because they are mounted in a thin plastic channel, and only need to be deformed slightly sideways to get jammed.

Luckily, if you have this problem, most built-in card readers are easy to pull apart and repair; some users have even reported succesfully unjamming the switch with a blast of compressed air from a can into the SD-card slot without having to dislodge anything. You may also be able to temporarily get round the problem by putting the write-protect tab in a half-way position - this pushes on a different part of the strip and may break the contact - it's worth trying a few, slightly different positions. You could also use a USB-SD card adaptor, which are cheap to buy.

SD(DC|DX] Card Class 6 & 10 Hints

[card usage Hints with OverClocking ]


Ethernet connection is lost when a USB device is plugged in

This is often caused by inadequate power. Use a good power supply and a good power cable. Some cheap cables that work with a cell phone, cannot fully power the R-Pi. Some USB devices require a lot of power (>100 mA), so they must be used with a powered USB hub. Some cheap USB hubs suck power from the Raspberry Pi even if a USB power supply is connected. (More often than not, however, the reverse is true with cheap hubs—the Pi draws just enough power backwards from the powered hub to unsuccessfully attempt booting.)

There is an ongoing issue with the Ethernet connection being lost when low-speed devices, such as mice or keyboards are connected via a powered USB hub. The simplest way to solve this is to connect your mouse and keyboard directly into the 2 USB ports on the R-Pi (assuming they draw less than 100 mA apiece).

Ethernet connects at 10M instead of 100M

The LED in the corner of the board labelled "10M" is mislabeled on the rev 1.0 PC board. It is correctly labeled "100" on the rev 2.0 PC board. When that LED is on, RasPi is connected at 100 Mbps. You can confirm the true transfer rate using a network benchmark such as iperf. You can also read the current network speed with:

 cat /sys/class/net/eth0/speed

Cannot ssh in to Pi

In the Debian image, ssh is disabled by default. Boot commands are taken from /boot/boot.rc if that file present. There is an example file named boot_enable_ssh.rc that enables ssh. So:

sudo mv /boot/boot_enable_ssh.rc /boot/boot.rc

and reboot should enable ssh. (password as below)

Network/USB chip gets too hot to touch

This is normal. In open air at 24 C, the LAN9512 Ethernet/USB chip reaches about 52 C after some time. This is too hot to touch for more than a few seconds, but it is not unusually hot for the chip.

The LAN9512 data sheet in Table 4.1 on p.40 says it comes in two versions, rated for operation at an ambient temperature in still air (Ta) of 70 C (commercial) or 85 C (industrial). It uses 763 mW at 3.3V with maximum traffic on 100baseT and both USB ports (Table 4.3.4, p. 42).

There is a study of RasPi heat profiles by "Remy" at ¿Se calienta el ordenador Raspberry Pi? Estudio de sus temperaturas en funcionamiento (Is the Raspberry Pi computer getting hot? A study of its operational temperature.) The Spanish article has numerous color temperature images of RasPi in various operational modes, with the highest LAN9512 case temperature measured as 64.5 C.

Networking no longer works when changing SD card between two Raspberry Pis

In some distributions, /etc/udev/rules.d/70-persistent-net.rules remembers which MAC address is associated with eth0, so each new device will be assigned as a different interface (eth1, eth2, etc.) due to the different MAC addresses. Editing /etc/udev/rules.d/70-persistent-net.rules to remove the invalid rules and rebooting may help fix the problem.

Crashes occur with high network load

The USB driver allocates memory from the kernel, and when traffic is very high (e.g. when using torrents/newsgroup downloads) this memory can be exhausted causing crashes/hangs. (Crashes with high network load can also be related to your power supply, try a powered usb hub.) You should have a line like:

vm.min_free_kbytes = 8192

in /etc/sysctl.conf. Try increasing that number to 16384. If that doesn't work, try adding to /boot/cmdline.txt


which will reduce network throughput, but has improved stability issues for some.

Under special circumstates additional /boot/cmdline.txt options are helpful (for example using RPi as Wifi Access-Point with high Network Traffic):

dwc_otg.dma_enable=1 dwc_otg.dma_burst_size=256

If the above fixes do not work, you can prevent the crashes by limiting the bandwidth (This is also working sometimes if the crashes are related to power supply.):

wondershaper wlan0 1500 1500 

This bandwidth (~150k/s) is enough to stream video with flvstreamer and omxplayer.

(wondershaper is available in raspian: sudo apt-get install wondershaper. You could also test limiting the bandwidth in advance with wget --limit-rate=150)

Network connection fails when a Graphical User Interface is being used

The network connection may fail when the command startx is used to enter a Graphical User Interface. This is caused by a bug in the USB driver related to certain types of USB mouse.

As of 1 September 2012, this fault is fixed in the latest firmware. To load the latest firmware, see http://elinux.org/R-Pi_Troubleshooting#Updating_firmware


I do not know the password to login

Please check the page http://www.raspberrypi.org/downloads for the correct username and password for each image.

Here are the most common username/password combinations:

  • Raspian "wheezy" pi/raspberry
  • Debian after Feb 2012: pi/raspberry
  • Debian 17 Feb 2012: pi/suse
  • Arch: root/root
  • Bodhi: pi/bodhilinux
  • Raspbx:root/raspberry
  • Kali Linux: root/toor

Some programs refuse to accept my password

While using Debian, some programs may ask for your password but refuse to accept a valid password.

This is a fault in old Debian images previous to September 2012. If you are using an image with this fault, upgrade to a more modern image or enter the following command on the command line.

gconftool-2  --type bool  --set  /apps/gksu/sudo-mode  true

Please enter this command carefully, the spaces are important. The command should be accepted without any response or errors.

I don't know the root password

There is no root password set by default on Debian. You are expected to do everything through sudo. You can set one with "sudo passwd root" - just make sure you know what you are doing with a root account.


Sound does not work with an HDMI monitor

This is caused by some computer monitors which select DVI mode even if an HDMI cable is connected. This fix may be necessary even if other HDMI devices work perfectly on the same monitor (or TV)!

Edit the configuration file - see the instructions at R-Pi_ConfigurationFile.

Add the following line to the configuration file /boot/config.txt:


This will force it to select HDMI mode.

You might need as well:


More reasons why sound does not work with an HDMI monitor

With an HDMI connection it might be possible to hear:

/opt/vc/src/hello_pi/hello_audio/hello_audio.bin 1

but not:

aplay /usr/share/sounds/alsa/Front_Center.wav

Firstly, it seems that some HD TVs mute audible sound output when there is no digital input, and slowly fade the sound up and down at the start and end of digital input. This means that short duration sounds will not be heard. A work around is to play longer duration wav files.

Secondly, it seems that some HD TVs mute audible sound output when there is only one channel of digital input. So, as the file Front_Center.wav is mono, it might not be heard. ALSA aplay uses the file information header to configure its digital output. And the aplay -c 2 option does not over-ride the settings aplay picks up from the file information header. So, if your HD TV doesn't accept just one channel of digital input, you cannot use aplay to hear a mono wav file. However, with the command speaker-test, the -c2 option does work, and sets 2 channels in the digital stream. So speaker-test can be used to hear the file Front_Center.wav in either the left or right speaker using the -s option 1 or 2. For example

speaker-test -c 2 -s 1 -t wav -W /usr/share/sounds/alsa -w Front_Center.wav

should be heard on the left speaker. But note that the command speaker-test seems only to like mono wav files, and seems not to play stereo wav files.

The command aplay plays 2 channel stereo wav files in stereo sound without problem (provided they last longer than the time it takes the TV to unmute and remute). A helpful example I found is the stereo file LRMonoPhase4.wav at the Kozco web site [4]

No sound card present

If no sound is being produced, and alsamixer is unable to show you any controls, the GPU may have disabled audio. Run this command to check:

 amixer controls

Which responds:

 amixer: Control default open error: No such file or directory

You can also confirm by checking for the existence of the directory '/proc/asound'.

This issue can be experienced when upgrading the kernel, due to changes in how the device tree defaulting has changed.

To correct this, assuming the device tree is enabled, add the following to '/boot/config.txt':


This can be unused along with other 'dtparam' settings, on the same line or different lines. Reboot, then check the amixer command again.

Sound does not work at all, or in some applications

Enter the command 'alsamixer' and use the control to check that the volume is up (arrow keys) and that the output is not muted (M key).

In Debian Squeeze, sound is disabled by default because the ALSA sound driver is still "alpha" (not fully tested) on the R-Pi. To install support for sound, type the following from a command line (from the command prompt before "startx" or in a terminal window)

 sudo apt-get update
 sudo apt-get upgrade
 sudo apt-get install alsa-utils
 sudo modprobe snd_bcm2835

On Debian Wheezy, snd_bm2835 is enabled by default, so the 'modprobe' step is not necessary. Next try:

 aplay /usr/share/sounds/alsa/Front_Center.wav

By default output will be automatic (hdmi if hdmi supports audio, otherwise analogue). You can force it with:

 amixer cset numid=3 <n>

where n is 0=auto, 1=headphones, 2=hdmi.

If you have pulseaudio installed you need to also specify the card number:

 amixer -c 0 cset numid=3 <n>

You can immediately verify if you hear a 440 Hz tune:

speaker-test -t sine -f 440 -c 2 -s 1

With recent firmware, you can build hello_audio with:

 cd /opt/vc/src/hello_pi/
 cd hello_audio

With older firmware

 cd /opt/vc/src/hello_pi/hello_audio

to test analogue output:



 ./hello_audio.bin 1

to test HDMI.

Also note that you may have to add your user to the 'audio' group to get permission to access the sound card.

Following this setup, you should be able to play wav files with the command

aplay /usr/share/scratch/Media/Sounds/Animal/Kitten.wav

Other command features can be found with

aplay --help

You will find numerous test files under /usr/share/scratch/Media/Sounds/ .

Removal of installed pulseaudio

Between December 2012 and February 2013 the standard raspbian wheezy distribution, and apt-get upgrade, included pulseaudio. Forum posts suggest that pulseaudio can break alsa. Whilst some members identify various workarounds, others find only removal of pulseaudio restores sound output.

sudo apt-get --purge remove pulseaudio

Playing MP3 files

The alsa app included in the standard distribution plays wav files. If you want to play mp3 files, do the following to install an mp3 player (after installing alsa-utils):

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install mpg321

You can play mp3 files with the command

mpg321 "my file.mp3"

Other command options can be determined with

mpg321 --help

The mp3 support with this app is complete but not robust.


Startx fails to start

If you just get errors instead of a desktop when typing


you may be out of storage space on the SD card. By default there are only a few hundred MB free in the 2 GB main partition, which can quickly fill up if you download files. Make sure there is some space free (gparted can expand a partition, if the SD card is > 2GB). Also, installing some software may incorrectly create or modify a .Xauthority file in your home directory, causing startx to fail, according to this thread. Temporarily renaming, moving, or deleting that file may fix the problem.

Screen is the wrong color

Check and see if the DVI cable is screwed in properly. If that doesn't work then try this section.

Video does not play or plays very slowly

The only hardware-accelerated video player is in the XBMC distribution and its command line variant omxplayer. H264 is the only hardware-accelerated codec, for playback. No hardware encoding is supported. Additional codecs were not purchased as licensing fees would have increased the R-Pi's price.

Notwithstanding the previous paragraph, omxplayer may be included in some versions of raspbian. It is a command line tool, and happily plays .flv files. Command: sudo omxplayer -o hdmi <path-to-filename>

Can only get 800x480 resolution in LXDE (Arch linux)

Known issue with distro package as of 17th April 2012 - there's some missing boot config information. Creating a suitable cmdline.txt fixes it - type the following at the Raspberry Pi command line:

  sudo echo "dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 root=/dev/mmcblk0p2 rootfstype=ext3 rootwait" >/boot/cmdline.txt

Big black borders around small image on HD monitors

Out of the box, R-Pi graphics don't necessarily fill the whole screen. This is due to something called "Underscan", and it can be fixed easily.

Note: the best solution is to disable overscan on the TV/monitor. Check the display menu options (it may be called "just scan", "screen fit", "HD size", "full pixel", "unscaled", "dot by dot", "native" or "1:1"), then use the disable_overscan=1 option.

Edit the configuration file, see the instructions at R-Pi_ConfigurationFile.

Add the following lines to the configuration file...

If your display has no overscan:


or if your display has some overscan:





Making the R-Pi graphics fill the screen is a matter of experimenting with the numbers you put in the config.txt file. Change the numbers – try jumps of 5 or 10 at a time. Bigger negative numbers reduce the black borders (so -40 means less black border than -20). The numbers do not all have to be the same; you can use this feature to centre the display on the screen.

This only affects the framebuffer (e.g. console or X). It doesn't affect hardware layers (like video/3D). You can make it apply to hardware layers with:


Writing spills off the screen on HD monitors

Out of the box, R-Pi graphics may be larger than the 1080p (ie Full HD) screen. This is due to something called "Overscan", and it can be fixed easily by creating a simple text file on the R-Pi SD card by using Notepad on your PC.

Follow the instructions in the section "Big black borders around small image on HD monitors", but use positive numbers for the overscan settings, for example





Interference visible on a HDMI or DVI monitor

This may be caused by loss of signal on long video cables. The signal level may be increased by changing a configuration parameter.

RPi HDMI interference.jpg

Edit the configuration file; see the instructions at Raspberry Pi configuration file.

Add the following line to the configuration file


You may experiment with different values of config_hdmi_boost. The default is 2 for Pi1 model A/B, and 5 for newer Pi's (B+, Pi2, Pi3). At your own risk, you can go up to 11.

Note that various adapters, such as HDMI-to-DVI, can also cause power loss and therefore require high values of config_hdmi_boost even with short cables.

This option can also help when there is no display output at all, the display periodically blanks, or colours are wrong/inverted.

This symptom can also be caused by RasPi +5V (measured from TP1 to TP2) falling too low. See Troubleshooting Power Problems.

No HDMI output at all

The PI's GPIO header P1 Source

First make sure the display is powered on and switched to the right input before booting Pi. If you have a case remove it as it can prevent your HDMI cable to properly connect to the HDMI port.

If you have the Rasbian Wheezy image (recommended) then try


Which will force the PI to boot in "safe mode".

For a quicker way to force wheezy into booting in safe mode, which doesn't need editing config.sys, you can also try to boot while holding the GPIO header P1-pin-5 (GPIO 1, SCL) low. This pin is normally held high with a pullup, but if you place a jumper between pin 5, (GPIO 1) and pin 6, (GND) of the GPIO header it will force the PI to boot in safe mode, which will force a 640x480 VGA screen mode, which any HDMI device should be able to display. Be very careful not to connect any other pins, especially not pins 1 and 2 (3V3 and 5V) as doing so, with power on, will damage your PI!

Otherwise, try adding the following line to the configuration file (similar to interference case above)


Your monitor/cable may not be asserting the hotplug signal. You can override this with:


A similar problem has occured following the installation of Rasbian Wheezy image "2013-02-09-wheezy-raspbian" - the hotplug signal appeared to be no longer detected when a HDMI 3 Port Switcher was in use for the Pi running from that image. An older, but updated and upgraded image still worked, as did a similar image on the other Pi connected to the switch, but, unless the above override was implemented, the Pi with the new image would only provide a HDMI display when directly connected to the monitor. The same problem has re-occurred when using that wheezy image with a new (in March 2013) "Model A" Pi.

Also try the following video options:


which resolved an issue with DVI monitor reporting "input signal out of range"

As a last resort, try deleting (rename to keep backup) config.txt from the SD card.

Also check that the RasPi +5V voltage (measured from TP1 to TP2) is in the correct range. One user found that his DVI-D monitor blanked out when +5V was too low. See Troubleshooting Power Problems.

Here's a rare cause: A standard HDMI cable has five individual ground wires plus a shield. Some cheap HDMI cables do not implement the individual grounds and just have a common foil shield that's connected to the HDMI plug shells at both ends. This works OK in most HDMI applications since most HDMI sources (like RasPi) and most monitors connect the shells to circuit ground. However, some HDMI or DVI monitors may requires individual ground lines. You can tell if an HDMI cable implements the individual grounds by checking for continuity using an Ohmmeter or multimeter. You can find the HDMI pinout for full-size connectors at Wikipedia.

Composite displays no image

The output display should default to HDMI if an HDMI display is connected, and composite if not (the composite output is the yellow RCA phono connector). At boot time, the Pi tries to detect an HDMI cable. If it cannot detect an HDMI cable it defaults to using composite output. Therefore, make sure there isn't a HDMI cable connected when you want to use composite output. Also, the Pi will only auto-detect once, at boot-time. If you want to switch from HDMI to Composite or back you need to reboot (or know the appropriate command-line magic).

If you expected to get composite output and you do not, the problem is either with the Pi output, with the cable or with the TV/monitor. Here are some things to try

  • Are you using the NOOBS GUI for OS installation and selection? On the first boot, i.e. when installing, you can hold 3 (PAL) or 4 (NTSC) while booting to force composite. If you install with HDMI and later want to change, alternately press SHIFT then 3 or 4 while booting: SHIFT takes you to the install screen, where 3 and 4 are recognized. You can then choose whether to make the change permanent, and press Esc to go back to the OS selection screen.
  • Is the Pi configuration forcing HDMI output? Inspect the file "config.txt" in the boot partition of your memory card and look for the line "hdmi_force_hotplug=1". If you see this line, comment it out (in particular, look at the end of "config.txt", in the section entitled "NOOBS Auto-generated Settings:")
  • Is the cable connection ok? If you're using a cable with red/white/yellow phonos on each end, make sure you're plugging in the yellow at both ends, and make sure it is pushed home fully into the socket. Try using (e.g.) the white connectors at each end, instead.
  • Are you using the correct connection on the TV/monitor? You need to be using a composite input, which will usually be a yellow RCA phono connector. This is NOT the same as the (RF modulated) antenna connection. If your TV has a SCART input you can buy a SCART Composite adaptor that has a set of RCA phono connectors. If you're already using one of those connectors, make sure that the switch on it is set to IN.
  • Have you selected the correct input on the TV/Monitor? It's normally marked "AV". If your TV has multiple AV inputs, try all of the inputs, normally by pressing a button marked "AV" or "Input" or "Source" or "->O" on the remote control. If you have other things connected to the TV AV inputs they may have a higher "priority" in. Try disconnecting them.
  • Are you being impatient? It takes about 7s from power-up for the Pi to start driving the composite output. With everything wired up, and the correct source selected on the monitor, power up the Pi and start counting. After about 7s you may see a brief white flicker or flash on the screen. That is the Pi considering using the composite output and choosing not to. If you see this, the problem is probably in your config.txt
  • Is everything good apart from the TV? One user suggested connecting the composite output to the audio input (red or white RCA phono) e.g. on a mini HiFi system. Keep the volume right down low. After power-up you should hear a couple of clicks. After about 7s you should hear a near-constant throbbing buzz, changing tone a couple of times after a few seconds (that's the desktop starting up, I think). If you power-cycle and then do the same thing with an HDMI cable connected (even with nothing connected at the far end of the HDMI cable) you should hear the clicks just after power-up and then no more sound.
  • Is the Pi faulty? This is unlikely and you should consider it only as a last resort.

Composite displays only black and white image

The composite display defaults to NTSC (American) output. Most TVs will show an image with that, but older PAL (European) televisions may display only back and white or no image. To fix this:

Edit the configuration file, see the instructions at R-Pi_ConfigurationFile.

Add the following line to the configuration file


(You can try other values: 0 is NTSC, 1 is Japanese NTSC, 2 is PAL, 3 is Brazilian PAL)

HDMI -> VGA adapters

Some good information can be found here:

A commonly used adapter from Ebay: gallery with detailed images & steps of a modification to use external power source: HERE --by Pinoccio



Remember that the GPIO pins are 3.3V logic level only, and are NOT 5V tolerant.

If you momentarily shorted the two end GPIO pins together (+3.3V and +5V), or a supply pin to ground, and the Pi appears to be dead, don't panic. The input polyfuse may have tripped. It is self-resetting after it cools down and the polymer re-crystallizes, which can take several hours. Set the Pi aside and try again later.

The GPIO pins connect directly into the core of the ARM processer, and are static-sensitive, so you should avoid touching the pins wherever possible. If you are carrying a static charge, for example by taking off an acrylic pullover, or walking across a nylon carpet, touching the GPIO pins could destroy your R-Pi, so always earth yourself before touching the pins or anything connected to them.


If you think you have damaged one or more gpios you can carry out a diagnostic test.

The test is a bash (command line) script called gpiotest

The test requires the services of the pigpio library.

For the duration of the test nothing must be connected to the gpios (no LEDs, wires, ribbon cables etc.).

The test checks that each gpio may be read and written and that the internal resistor pull-ups and pull-downs are functional.

A video showing what happens to the gpios during a test.

A test with all gpios okay.

This program checks the Pi's (user) gpios.

The program reads and writes all the gpios.  Make sure NOTHING
is connected to the gpios during this test.

The program uses the pigpio daemon which must be running.

To start the daemon use the command sudo pigpiod.

Press the ENTER key to continue or ctrl-C to abort...

Skipped non-user gpios: 0 1 28 29 30 31 
Tested user gpios: 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 
Failed user gpios: None

A test showing failed gpios.

This program checks the Pi's (user) gpios.

The program reads and writes all the gpios. Make sure NOTHING
is connected to the gpios during this test.

The program uses the pigpio daemon which must be running.

To start the daemon use the command sudo pigpiod.

Press the ENTER key to continue or ctrl-C to abort...

Write 1 to gpio 17 failed.
Pull up on gpio 17 failed.
Write 1 to gpio 18 failed.
Pull up on gpio 18 failed.
Write 0 to gpio 23 failed.
Pull down on gpio 23 failed.
Write 0 to gpio 24 failed.
Pull down on gpio 24 failed.
Write 1 to gpio 27 failed.
Pull up on gpio 27 failed.
Skipped non-user gpios: 0 1 28 29 30 31
Tested user gpios: 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
Failed user gpios: 17 18 23 24 27

Digital Waveform Viewer

A logic analyser or a digital waveform viewer is a very useful tool to diagnose problems with the gpios.

piscope is a digital waveform viewer which lets you see what is happening on the gpios in a live view.

A video of a capture session.

Some screen captures.


The time is incorrect

If the clock is off by a series of hours, in the command line type:

sudo dpkg-reconfigure tzdata

The R-Pi has no real-time clock, so unless it can access a timeserver over the network at boot, or time is manually entered by the user, the time/date will restart counting from the last logged time in the previous session.

A part broke off

The silver cylinder near the microUSB power input is a 220 uF capacitor ("C6" on schematic). It sticks up and due to the small surface-mount pads, it is easy to break off; several people have done so. This is a power supply filter capacitor which reduces any noise and spikes on the input +5V power. If you like, you can solder it back on, or just leave it off. If you do solder it back on, take care to observe the correct polarity with the black stripe towards the board edge. This part, C6 is a "just in case" component which is good design practice to include, but as it turns out most power supplies still work OK without this part installed. This part is also discussed here.

Unable to install new software

When trying to install a software package (using the command sudo apt-get install xxxx) you may see the error

Package yyyy is not available

This means that your software list is out of date. Before attempting to install software, you should always make sure that you are using the latest software list by using the commands

sudo apt-get update
sudo apt-get upgrade

Troubleshooting power problems

If you think you have a problem with your power supply, it is a good idea to check the actual voltage on the Raspberry Pi circuit board. Two test points labelled TP1 and TP2 are provided on the circuit board to facilitate voltage measurements.

Use a multimeter which is set to the range 20 volts DC (or 20v =). You should see a voltage between 4.75 and 5.25 volts. Anything outside this range indicates that you have a problem with your power supply or your power cable.

If you have not used a multimeter before, see these [basic instructions]

Note: Even if the multimeter shows the correct voltage, you may have some power supply problems. A multimeter only displays the average voltage. If there are very short-lived dips or spikes in the voltage, these will not be shown by the multimeter. It is best to measure voltage when Pi is busy.

If your voltage is low, it could be:

  • The power supply produces too low a voltage
  • The power supply cannot supply enough current, which results in a voltage drop. Make sure Power supply is labelled as at least 700mA. (Some cheap power supplies don't deliver what is labelled).
  • The Micro USB power cable is low quality. Some Micro USB cables have very thin conductors, resulting in enough voltage drop for RasPi to fail even if the power supply itself is fine. For details, see On_the_RPi_usb_power_cable.
  • Attached USB devices want too much power. The Pi is only designed for up to 100mA USB devices. A USB device wanting more that that will cause a voltage drop.
  • The F3 Polyfuse could be blown or bad, see below for how to test.

Note: keyboards with LCD displays, built in USB hubs, backlights, etc are likely to be problematic. Try to use a basic one. Wifi dongles are also unlikely to work when directly connected. Connect high powered USB devices to a powered USB hub.

Try booting without HDMI, ethernet or USB deviced plugged in, and see if the voltage improves. See also: Power Supply Problems

RPI Test Points.JPG Voltmeter.JPG

How to test the F3 polyfuse[19]

  1. Remove all the things plugged into your Raspberry Pi, including SD card.
  2. Locate the TP2 test point on the top of the board.
  3. Turn your board over and find the TP2 test point on the bottom of the board. One lead of your multi-meter will always be on the TP2 point on the bottom of the board for all tests.
  4. Plug your power supply into the micro usb port and power your board.
  5. Place one lead of your multi-meter on the TP2 point on the bottom of the board and one lead on the side of the F3 fuse closest to the edge of the board. Note the voltage. This is the voltage coming into your RPi from your power supply.
  6. Keeping one lead on TP2, move the other lead to the side of F3 closest to the SD card slot. This is the voltage coming out of the F3 fuse.
Multi-meter lead placement for testing the Raspberry Pi F3 Polyfuse

If the voltage is different by more than about 0.3v you probably have an issue with the F3 fuse[20].

When polyfuses "blow" their resistance increases dramatically, there by limiting the voltage that can pass through them. If your power problem suddenly appeared after your board was known to be working fine, it is probable the fuse is just "blown" and will return to normal. Polyfuses recover from the tripped state to near their normal value in a few minutes, but do take some hours to fully recover so leave it unpowered and check it again in a little while.[21] If your power problem has been since the first time you plugged in your board, the fuse was probably bad when it arrived and should be returned to place you purchased it.

Also, on a related issue, do note that if you do not power the PI in the "official manner", that is through it's micro-USB port, but use any alternative way (such as through the GPIO header, the test points TP1 and TP2), but also by back-powering it, you are actually bypassing the PI's input polyfuse protection device! This can have extreme consequences if ever you manage to put more than 6V on the PI, even for a very short period. As this causes the overvoltage device D17 on the the PI to trigger and short the 5V supply! Without the polyfuse limiting the current through D17, it will burn out, probably melting the PI's enclosure with it, (if you have any) and possibly causing a fire-hazard. It will probably also create a permanent short of the 5V supply! So be warned, and if you use back power make sure your hub or its PSU has a fuse to prevent this from happening. If not, add your own fuse.

If you prefer to make your own PSU - see: Power Supply construction - HowTo

Hardware versions/revisions

Several different boards have been found probably from different assembly lines, and the following tables try to help you identify your board for better troubleshooting.

Look for the date of manufacturing printed with the year and week. In this example year (2012) and week (18th):

Date of manufacturing.jpg

For what we can see for model B boards there are mainly two versions that differ on the type RAM used, Samsung (S) and Hynix (H).

For Board ver. we used: <model><RAM Maker><production date> (ex.: BS1218 is "Model B, Samsung RAM, 18th week of 2012")

Model A:







Front Back

Model B:







Front Back
BS12xx Samsung SMSC
RaspberryPi-Board A-Front.JPG
RaspberryPi-Board A-Back.JPG
BH12xx Hynix SMSC
RaspberryPi-Board B-Front.JPG
RaspberryPi-Board B-Back.JPG

See a complete list and user feedback here: RaspberryPi Boards


  1. http://www.raspberrypi.org/phpBB3/viewtopic.php?f=28&t=7528
  2. http://www.raspberrypi.org/documentation/hardware/raspberrypi/schematics/Raspberry-Pi-B-Plus-V1.2-Schematics.pdf
  3. http://www.mouser.com/ds/2/115/APX803_D-86185.pdf
  4. http://www.raspberrypi.org/phpBB3/viewtopic.php?f=6&t=5096&p=76503#p76503
  5. http://www.raspberrypi.org/phpBB3/viewtopic.php?f=6&t=5096&p=76654#p76654
  6. http://www.raspberrypi.org/forum/troubleshooting/will-not-boot-consistently-any-suggestions-before-i-send-my-pi-back
  7. http://www.raspberrypi.org/forum/troubleshooting/booted-once-wont-work-again
  8. http://www.raspberrypi.org/forum/troubleshooting/possible-fault-pi-boots-sometimes-but-not-always
  9. http://www.raspberrypi.org/phpBB3/viewtopic.php?f=6&t=5900&p=79008#p79008
  10. http://www.raspberrypi.org/phpBB3/viewtopic.php?f=6&t=5900&p=78973#p78973
  11. https://github.com/raspberrypi/linux/commit/e09244e60881148431ecd016ccc42f1fa0678556
  12. http://www.raspberrypi.org/forum/troubleshooting/usb-power-hub-wifi/page-4#p74609
  13. http://www.raspberrypi.org/forum/troubleshooting/success-with-kb-mouse-wifi?value=3761&type=8&include=1&search=1
  14. http://www.raspberrypi.org/forum/troubleshooting/display-and-keyboard-issues-on-a-real-pi#p74816
  15. http://www.raspberrypi.org/phpBB3/viewtopic.php?f=28&t=7533
  16. http://www.raspberrypi.org/phpBB3/viewtopic.php?t=5766#p77576
  17. http://www.raspberrypi.org/phpBB3/viewtopic.php?t=5766#p80995
  18. http://www.raspberrypi.org/phpBB3/viewtopic.php?f=28&t=6822&p=89589&hilit=eben#p89513
  19. http://www.raspberrypi.org/phpBB3/viewtopic.php?f=26&t=22318
  20. http://www.raspberrypi.org/phpBB3/viewtopic.php?f=28&t=24005&p=222526#p222526
  21. http://www.raspberrypi.org/phpBB3/viewtopic.php?f=28&t=24005&p=222549#p222543