config.txt

As it’s an embedded platform, the Raspberry Pi doesn’t have a BIOS like you’d find on a conventional PC. The various system configuration parameters, which would traditionally be edited and stored using a BIOS, are stored in an optional text file named config.txt. This is read by the GPU before the ARM CPU (and Linux) is initialised; therefore it must be located on the first (boot) partition of your SD card, alongside bootcode.bin and start.elf. This file is normally accessible as /boot/config.txt from Linux and must be edited as root; but from Windows or OS X it is seen as a file in the only accessible part of the card. If you need to apply some of the config settings below, but you don’t have a config.txt on your boot partition yet, then simply create it as a new text file.

Any changes will only take effect after you’ve rebooted your Raspberry Pi. After Linux has booted you can get the current active settings with the following commands:

vcgencmd get_config <config> - displays a specific config value, e.g. vcgencmd get_config arm_freq.

vcgencmd get_config int - lists all the integer config options that are set (non-zero).

vcgencmd get_config str - lists all the string config options that are set (non-null).

Note that there’s a small number of config settings that can’t be retrieved using vcgencmd.

File format

As config.txt is read by the early-stage boot firmware it has a very simple file format. The format is a single property=value statement on each line, where value is either an integer or a string. Comments may be added, or existing config values may be commented out and disabled by starting a line with the # character.

Here is an example file:

# Force the monitor to HDMI mode so that sound will be sent over HDMI cable
hdmi_drive=2
# Set monitor mode to DMT
hdmi_group=2
# Set monitor resolution to 1024x768 XGA 60Hz (HDMI_DMT_XGA_60)
hdmi_mode=16
# Make display smaller to stop text spilling off the screen
overscan_left=20
overscan_right=12
overscan_top=10
overscan_bottom=10

Memory

gpu_mem

GPU memory in megabytes. Sets the memory split between the CPU and GPU; the CPU gets the remaining memory. Minimum value is 16; maximum value is either 192, 448 or 944 depending on whether you’re using a 256M, 512MB or 1024MB Pi. The default value is 64.

Setting gpu_mem to low values may automatically disable certain firmware features (as there are some things the GPU simply can’t do with too little memory). So if a certain feature you’re trying to use isn’t working, try setting a larger GPU memory split.

Using gpu_mem_256, gpu_mem_512 and gpu_mem_1024 allows you to swap the same SD card between 256MB, 512MB and 1024MB Pis without having to edit config.txt each time:

gpu_mem_256

GPU memory in megabytes for the 256MB Raspberry Pi (ignored if memory size is not 256M). This overrides gpu_mem. The maximum value is 192 and the default is not set.

gpu_mem_512

GPU memory in megabytes for the 512MB Raspberry Pi (ignored if memory size is not 512M). This overrides gpu_mem. The maximum value is 448 and the default is not set.

gpu_mem_1024

GPU memory in megabytes for the 1024MB Raspberry Pi 2 (ignored if memory size is not 1024M). This overrides gpu_mem. The maximum value is 944 and the default is not set.

disable_l2cache

Setting this to 1 disables the CPU’s access to the GPU’s L2 cache; requires a corresponding L2 disabled kernel. Default value is 0.

disable_pvt

Setting this to 1 disables adjusting the refresh rate of RAM every 500ms; this action measures the RAM’s temperature. Default value is 0.

CMA - Dynamic memory split

The firmware and kernel as of 19th November 2012 supports CMA (Contiguous Memory Allocator), which means the memory split between CPU and GPU is managed dynamically at runtime. However this is not officially supported.

You can find an example config.txt here.

cma_lwm

When the GPU has less than cma_lwm (low-water mark) megabytes of memory available, it will request some from the CPU.

cma_hwm

When the GPU has more than cma_hwm (high-water mark) megabytes of memory available, it will release some to the CPU.

The following options need to be in cmdline.txt for CMA to work:

coherent_pool=6M smsc95xx.turbo_mode=N

Camera

disable_camera_led

Setting this to 1 prevents the red camera LED from turning on when recording video or taking a still picture. Useful for preventing reflections when the camera is facing a window.

Onboard Analogue Audio (3.5mm jack)

The onboard audio output has a few config options that alter the behaviour of how the analogue audio is driven and whether some firmware features are enabled or not.

disable_audio_dither

By default, a 1.0LSB dither is applied to the audio stream if it’s routed to the analogue audio output. This can create audible background “hiss” in some situations, such as if the ALSA volume is set to a low level. Set this to 1 to disable dither application.

pwm_sample_bits

Adjust the bit depth of the analogue audio output. The default bit depth is 11. Selecting bit depths below 8 will result in nonfunctional audio - settings below 8 result in a PLL frequency too low to support. Generally only useful as a demonstration of how bit depth affects quantisation noise.

Video

Composite video mode options

sdtv_mode

Defines the TV standard used for composite video output over the yellow RCA jack; the default value is 0.

sdtv_aspect

This defines the aspect ratio for composite video output. The default value is 1.

sdtv_disable_colourburst

Setting this to 1 disables colour burst on composite video output. The picture will be displayed in monochrome, but it may possibly be sharper.

HDMI mode options

hdmi_safe

Setting this to 1 uses “safe mode” settings to try to boot with maximum HDMI compatibility. This is the same as setting the following parameters:

hdmi_force_hotplug=1
hdmi_ignore_edid=0xa5000080
config_hdmi_boost=4
hdmi_group=2
hdmi_mode=4
disable_overscan=0
overscan_left=24
overscan_right=24
overscan_top=24
overscan_bottom=24

hdmi_ignore_edid

Setting this to 0xa5000080 enables the ignoring of EDID/display data if your display doesn’t have an accurate EDID. It requires this unusual value to ensure that it doesn’t get triggered accidentally.

hdmi_edid_file

Setting this to 1, will cause the GPU to read EDID data from the edid.dat file, located in the boot partition, instead of reading it from the monitor. More information is available here.

hdmi_force_edid_audio

Setting this to 1 pretends that all audio formats are supported by the display, allowing passthrough of DTS/AC3 even when not reported as supported.

hdmi_ignore_edid_audio

Setting this to 1 pretends that all audio formats are unsupported by the display. This means ALSA will default to the analogue audio (headphone) jack.

hdmi_force_edid_3d

Setting this to 1 pretends that all CEA modes support 3D, even when the EDID doesn’t indicate support for them.

avoid_edid_fuzzy_match

Setting this to 1 avoids “fuzzy matching” of modes described in the EDID. Instead it will pick the standard mode with the matching resolution and closest framerate, even if blanking is wrong.

hdmi_ignore_cec_init

Setting this to 1 will prevent the initial active source message being sent during bootup. This avoids bringing a CEC-enabled TV out of standby and channel switching when rebooting your Raspberry Pi.

hdmi_ignore_cec

Setting this to 1 pretends that CEC is not supported at all by the TV. No CEC functions will be supported.

hdmi_pixel_encoding

Force the pixel encoding mode. By default it will use the mode requested from the EDID, so it shouldn’t need changing.

hdmi_drive

This allows you to choose between HDMI and DVI output modes.

config_hdmi_boost

Configures the signal strength of the HDMI interface; the default value is 0 and the maximum is 7. Try 4 if you have interference issues with HDMI.

hdmi_group

This defines the HDMI output group to be either CEA (Consumer Electronics Association; the standard typically used by TVs) or DMT (Display Monitor Timings; the standard typically used by monitors). This setting should be used in conjunction with hdmi_mode.

hdmi_mode

This, together with hdmi_group, defines the HDMI output format.

For setting a custom display mode not listed here, see this thread.

These values are valid if hdmi_group=1 (CEA):

In the table above, the modes with a 16:9 aspect ratio are a widescreen variant of a mode which usually has 4:3 aspect ratio. Pixel doubling and quadrupling indicates a higher clock rate, with each pixel repeated two or four times respectively.

These values are valid if hdmi_group=2 (DMT):

Note that there is a pixel clock limit, which means the highest supported mode is 1920x1200 at 60Hz with reduced blanking.

Which values are valid for my monitor?

Your HDMI monitor may support only a limited set of formats. To find out which formats are supported, use the following method:

1. Set the output format to VGA 60Hz (hdmi_group=1 and hdmi_mode=1) and boot up your Raspberry Pi
2. Enter the following command to give a list of CEA supported modes: /opt/vc/bin/tvservice -m CEA
3. Enter the following command to give a list of DMT supported modes: /opt/vc/bin/tvservice -m DMT
4. Enter the following command to show your current state: /opt/vc/bin/tvservice -s
5. Enter the following commands to dump more detailed information from your monitor: /opt/vc/bin/tvservice -d edid.dat; /opt/vc/bin/edidparser edid.dat

The edid.dat should also be provided when troubleshooting problems with the default HDMI mode.

Custom mode

If your monitor requires a mode that is not in one of the tables above, then it is possible to define a custom CVT mode for it instead:

hdmi_cvt=<width> <height> <framerate> <aspect> <margins> <interlace> <rb>

(Fields at the end can be omitted to use the default values.)

Note that this simply creates the mode (group 2 mode 87); in order to make the Pi use this by default you must add some additional settings. As an example, the following selects an 800x480 resolution and enables audio drive:

hdmi_cvt=800 480 60 6
hdmi_group=2
hdmi_mode=87
hdmi_drive=2

This may not work if your monitor does not support standard CVT timings.

Generic display options

hdmi_force_hotplug

Setting this to 1 pretends that the HDMI hotplug signal is asserted, so it appears that a HDMI display is attached. In other words, HDMI output mode will be used even if no HDMI monitor is detected.

hdmi_ignore_hotplug

Setting this to 1 pretends that the HDMI hotplug signal is not asserted, so it appears that a HDMI display is not attached. In other words, composite output mode will be used even if an HDMI monitor is detected.

disable_overscan

Set to 1 to disable overscan.

overscan_left

Specifies the number of pixels to skip on the left edge of the screen. Increase this value if the text flows off the left edge of the screen; decrease it if there’s a black border between the left edge of the screen and the text.

overscan_right

Specifies the number of pixels to skip on the right edge of the screen.

overscan_top

Specifies the number of pixels to skip on the top edge of the screen.

overscan_bottom

Specifies the number of pixels to skip on the bottom edge of the screen.

framebuffer_width

Specifies the console framebuffer width in pixels. The default is the display width minus the total horizontal overscan.

framebuffer_height

Specifies the console framebuffer height in pixels. The default is the display height minus the total vertical overscan.

framebuffer_depth

Specifies the console framebuffer depth in bits per pixel. The default value is 16.

framebuffer_ignore_alpha

Set to 1 to disable the alpha channel. Can help with the display of a 32bit framebuffer_depth.

test_mode

Displays a test image and sound during boot (but only over the composite video and analogue audio outputs) for the given number of seconds, before continuing to boot the OS as normal. This is used as a manufacturing test; the default value is 0.

display_rotate

Can be used to rotate or flip the screen orientation; the default value is 0.

Note that the 90 and 270 degree rotation options require additional memory on the GPU, so these won’t work with the 16MB GPU split.

Licence keys/codecs

Hardware decoding of additional codecs can be enabled by purchasing a licence that is locked to the CPU serial number of your Raspberry Pi.

decode_MPG2

Licence key to allow hardware MPEG-2 decoding, e.g. decode_MPG2=0x12345678.

decode_WVC1

Licence key to allow hardware VC-1 decoding, e.g. decode_WVC1=0x12345678.

If you’ve got multiple Raspberry Pis, and you’ve bought a codec licence for each of them, you can list up to 8 licence keys in a single config.txt; for example decode_MPG2=0x12345678,0xabcdabcd,0x87654321. This enables you to swap the same SD card between the different Pis without having to edit config.txt each time.

Boot

disable_commandline_tags

Set to 1 to stop start.elf from filling in ATAGS (memory from 0x100) before launching the kernel.

cmdline

The alternative filename on the boot partition to read the kernel command line string from; the default value is cmdline.txt.

kernel

The alternative filename on the boot partition to use when loading the kernel; the default value is kernel.img.

kernel_address

The memory address into which the kernel image should be loaded.

kernel_old

Set to 1 to load the kernel at the memory address 0x0.

ramfsfile

Optional filename on the boot partition of a ramfs to load. More information is available here.

ramfsaddr

The memory address into which the ramfsfile should be loaded.

initramfs

This specifies both the ramfs filename and the memory address to load it at; it performs the actions of both ramfsfile and ramfsaddr in one parameter. Example values are: initramfs initramf.gz 0x00800000. NOTE: This option uses different syntax to all the other options; you should not use a = character here.

init_uart_baud

The initial UART baud rate; the default value is 115200.

init_uart_clock

The initial UART clock frequency; the default value is 3000000 (3MHz).

init_emmc_clock

The initial emmc clock frequency; the default value is 100000000 (100MHz).

bootcode_delay

Wait for a given number of seconds in bootcode.bin before loading start.elf; the default value is 0.

This is useful in particular to insert a delay before reading the EDID of the monitor, which can be useful if the Pi and monitor are powered from the same source but the monitor takes longer to start up than the Pi. Try setting this value if the display detection is “wrong” on initial boot but correct if you soft-reboot the Pi without removing power from the monitor.

boot_delay

Wait for a given number of seconds in start.elf before loading the kernel; the default value is 1. The total delay in milliseconds is calculated as (1000 x boot_delay) + boot_delay_ms. This can be useful if your SD card needs a while to ‘get ready’ before Linux is able to boot from it.

boot_delay_ms

Wait for a given number of milliseconds in start.elf, together with boot_delay, before loading the kernel. The default value is 0.

avoid_safe_mode

If set to 1, safe_mode boot won’t be enabled. The default value is 0.

disable_splash

If set to 1, don’t show the rainbow splash screen on boot. The default value is 0.

Device Tree

There are several config.txt parameters related to Device Tree setup, and these are documented separately here.

Overclocking

NOTE: Setting any overclocking parameters to values other than those used by raspi-config will set a permanent bit within the SoC, making it possible to detect that your Pi has been overclocked. This was originally set to detect a void warranty if the device had been overclocked. Since September 19th 2012 you have been able to overclock your Pi without affecting your warranty; for more information see the blog post on Turbo Mode.

The latest kernel has a cpufreq kernel driver with the “ondemand” governor enabled by default. It has no effect if you have no overclock settings; if you overclock, the CPU frequency will vary with processor load. Non-default values are only used when needed according to the governor. You can adjust the minimum values with the *_min config options, or disable dynamic clocking with force_turbo=1; for more information see here.

Overclocking and overvoltage will be disabled at runtime when the SoC reaches 85°C to cool it down. You should not hit the limit, even with maximum settings at 25°C ambient temperature; for more information see here.

Overclocking options

force_turbo

force_turbo=0

This enables dynamic clocks and voltage for the CPU, GPU core and SDRAM. When busy, the CPU frequency goes up to arm_freq and down to arm_freq_min on idle.

core_freq/core_freq_min, sdram_freq/sdram_freq_min and over_voltage/over_voltage_min behave in a similar manner. over_voltage is limited to 6 (1.35V). Non-default values for the h264/v3d/isp frequencies are ignored.

force_turbo=1

Disables dynamic frequency clocking, so that all frequencies and voltages stay high. Overclocking of h264/v3d/isp GPU parts is allowed, as well as setting over_voltage up to 8 (1.4V). For more information see here.

Clocks relationship

The GPU core, h264, v3d, and ISP blocks all share a PLL and therefore need to have related frequencies. The CPU, SDRAM and GPU each have their own PLLs and can have unrelated frequencies; for more information see here.

The frequencies are calculated as follows:

pll_freq = floor(2400 / (2 x core_freq)) x (2 x core_freq)
gpu_freq = pll_freq / [even number]

The effective gpu_freq is automatically rounded to the nearest even integer; asking for core_freq=500 and gpu_freq=300 will result in the divisor of 2000/300 = 6.666 => 6 and so result in a gpu_freq of 333.33MHz.

avoid_pwm_pll

Setting this to 1 will decouple a PLL from the PWM hardware. This will result in more hiss on the analogue audio output, but will allow you to set the gpu_freq independently of the core_freq.

Monitoring temperature and voltage

To view the Pi’s temperature, type: cat /sys/class/thermal/thermal_zone0/temp. Divide the result by 1000 to get the value in Celsius.

To view the Pi’s current frequency, type: cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq. Divide the result by 1000 to get the value in MHz.

To monitor the Pi’s PSU voltage, you’ll need a multimeter to measure between the TP1 and TP2 power supply test points; more information is available in power.

It’s generally a good idea to keep the core temperature below 70 degrees and the voltage above 4.8V. Note that some USB power supplies fall as low as 4.2V; this is because they are usually designed to charge a 3.7V LiPo battery, rather than to supply 5V to a computer. If your overclocked Raspberry Pi is getting hot a heatsink can be helpful, especially if the Pi is to be run inside a case. A suitable heatsink is the self-adhesive BGA (ball-grid-array) 14x14x10 mm heatsink, available from RS Components.

Overclocking problems

Most overclocking issues show up immediately with a failure to boot. If this occurs, hold down the shift key during the next boot which will temporarily disable all overclocking; this will allow you to boot successfully and then edit your settings.

Conditional Filters

When a single SD card (or card image) is only being used with one Pi and one monitor, it’s easy to simply set config.txt as required for that specific combination and keep it that way, amending only when something changes.

However if one Pi is swapped between different monitors, or if the SD card (or card image) is being swapped between multiple Pis, a single set of settings may no longer be sufficient. Conditional filters allow you to make certain sections of the config file used only in specific cases, allowing a single config.txt to create different configurations when read by different hardware.

The [all] filter

This is the most basic filter: it resets all previously set filters and allows any settings listed below it to be applied to all hardware.

[all]

It is usually a good idea to add an [all] filter at the end of groups of filtered settings to avoid unintentionally combining filters (see below).

The [pi1] and [pi2] filters

Any settings below a [pi1] filter will only be applied to Pi1 (A, A+, B, B+) hardware. Any settings below a [pi2] filter will only be applied to Pi2 hardware.

[pi1]
[pi2]

These are particularly useful for defining different kernel, initramfs, and cmdline settings, as the Pi1 and Pi2 require different kernels. They can also be useful to define different overclocking settings for each, since they have different default speeds. For example, to define separate initramfs images for each:

[pi1]
initramfs initrd.img-3.18.7+ followkernel
[pi2]
initramfs initrd.img-3.18.7-v7+ followkernel
[all]

Remember to use the [all] filter at the end, so that any subsequent settings aren’t limited to Pi2 hardware only.

The [EDID=*] filter

When switching between multiple monitors while using a single SD card in your Pi, and where a blank config is not sufficient to automatically select the desired resolution for each one, this allows specific settings to be chosen based on the monitors’ EDID names.

To view the EDID name of a specific monitor, run the following command:

tvservice -n

This will print something like this:

device_name=VSC-TD2220

You can then specify settings that apply only to this monitor like so:

[EDID=VSC-TD2220]
hdmi_group=2
hdmi_mode=82
[all]

This forces 1920x1080 DVT mode for this monitor, without affecting any other monitors.

Note that these settings apply only at boot, so the monitor must be connected at boot time and the Pi must be able to read its EDID information to get the correct name. Hotplugging a different monitor after boot will not reselect different settings.

The serial number filter

Sometimes settings should only be applied to a single specific Pi, even if you swap the SD card to a different one. Examples include license keys and overclocking settings (although the license keys already support SD card swapping in a different way). You can also use this to select different display settings even if the EDID identification above is not possible for some reason (provided that you don’t swap monitors between your Pis) — for example if your monitor does not supply a usable EDID name or if you are using composite output (for which EDID cannot be read).

To view the serial number of your Pi, run the following command:

cat /proc/cpuinfo

The serial will be shown as a 16-digit hex value at the bottom. For example, if you see:

Serial          : 0000000012345678

Then you can define settings that will only be applied to this specific Pi like so:

[0x12345678]
# settings here are applied only to the Pi with this serial
[all]
# settings here are applied to all hardware

Combining conditional filters

Filters of the same type replace each other (so [pi2] overrides [pi1], as it is not possible for both to be true at once).

Filters of different types can be combined simply by listing them one after the other, eg:

# settings here are applied to all hardware
[EDID=VSC-TD2220]
# settings here are applied only if monitor VSC-TD2220 is connected
[pi2]
# settings here are applied only if monitor VSC-TD2220 is connected *and* on a Pi2
[all]
# settings here are applied to all hardware

Use the [all] filter to reset all previous filters and avoid unintentionally combining different filter types.

This article uses content from the eLinux wiki page RPiconfig, which is shared under the Creative Commons Attribution-ShareAlike 3.0 Unported license