On ARM-based systems in most cases one of two formats for boot images is used: a) standard Linux zImage-format kernels (vmlinuz) in conjunction with standard Linux initial ramdisks (initrd.gz) or b) uImage-format kernels (uImage) in conjunction with corresponding initial ramdisks (uInitrd). uImage/uInitrd are image formats designed for the u-boot firmware that is used on many ARM-based systems. Older u-boot versions can only boot files in uImage/uInitrd format, so these are often used on older armel systems. Newer u-boot versions can - besides booting uImages/uInitrds - also boot standard Linux kernels and ramdisk images, but the command syntax to do that is slightly different from that for booting uImages. For systems using a multiplatform kernel, besides kernel and initial ramdisk a so-called device-tree file (or device-tree blob, dtb) is needed. It is specific to each supported system and contains a description of the particular hardware. &boot-installer-intro-net.xml; Network booting on systems using the u-boot firmware consists of three steps: a) configuring the network, b) loading the images (kernel/initial ramdisk/dtb) into memory and c) actually executing the previosly loaded code. First you have to configure the network, either automatically via DHCP by running setenv autoload no dhcp or manually by setting several environment variables setenv ipaddr <ip address of the client> setenv netmask <netmask> setenv serverip <ip address of the tftp server> setenv dnsip <ip address of the nameserver> setenv gatewayip <ip address of the default gateway> If you prefer, you can make these settings permanent by running saveenv Afterwards you need to load the images (kernel/initial ramdisk/dtb) into memory. This is done with the tftpboot command, which has to be provided with the address at which the image shall be stored in memory. Unfortunately the memory map can vary from system to system, so there is no general rule which addresses can be used for this. On some systems, u-boot predefines a set of environment variables with suitable load addresses: kernel_addr_r, ramdisk_addr_r and fdt_addr_r. You can check whether they are defined by running printenv kernel_addr_r ramdisk_addr_r fdt_addr_r If they are not defined, you have to check your system's documentation for appropriate values and set them manually. For systems based on Allwinner SunXi SOCs (e.g. the Allwinner A10, architecture name sun4i or the Allwinner A20, architecture name sun7i), you can e.g. use the follwing values: setenv kernel_addr_r 0x46000000 setenv fdt_addr_r 0x47000000 setenv ramdisk_addr_r 0x48000000 When the load addresses are defined, you can load the images into memory from the previously defined tftp server with tftpboot ${kernel_addr_r} <filename of the kernel image> tftpboot ${fdt_addr_r} <filename of the dtb> tftpboot ${ramdisk_addr_r} <filename of the initial ramdisk image> The third part is setting the kernel commandline and actually executing the loaded code. U-boot passes the content of the bootargs environment variable as commandline to the kernel, so any parameters for the kernel and the installer - such as the console device (see ) or preseeding options (see and ) - can be set with a command like setenv bootargs console=ttyS0,115200 rootwait panic=10 The exact command to execute the previously loaded code depends on the image format used. With uImage/uInitrd, the command is bootm ${kernel_addr_r} ${ramdisk_addr_r} ${fdt_addr_r} and with native Linux images it is bootz ${kernel_addr_r} ${ramdisk_addr_r}:${filesize} ${fdt_addr_r} Note: When booting standard linux images, it is important to load the initial ramdisk image after the kernel and the dtb as u-boot sets the filesize variable to the size of the last file loaded and the bootz command requires the size of the ramdisk image to work correctly. In case of booting a platform-specific kernel, i.e. a kernel without device-tree, simply omit the ${fdt_addr_r} parameter. Many modern u-boot versions have USB support and allow booting from USB mass storage devices such as USB sticks. Unfortunately the exact steps required to do that can vary quite a bit from device to device. U-Boot v2014.10 has introduced a common commandline handling and autoboot framework. This allows building generic boot images that work on any system implementing this framework. The &d-i; supports installation from a USB stick on such systems, but unfortunately not all platforms have adopted this new framework yet. To build a bootable USB stick for installing &debian;, unpack the hd-media tarball (see ) onto a USB stick formatted with a filesystem supported by the u-boot version on your device. For modern u-boot versions, any of FAT16 / FAT32 / ext2 / ext3 / ext4 usually works. Then copy the ISO image file of the first &debian; installation CD or DVD onto the stick. The autoboot framework in modern u-boot versions works similar to the boot ordering options in a PC BIOS, i.e. it checks a list of possible boot devices for a valid boot image and starts the first one it finds. If there is no operating system installed, plugging in the USB stick and powering up the system should result in starting the installer. You can also initiate the USB-boot process any time from the u-boot prompt by entering the run bootcmd_usb0 command. One problem that can come up when booting from a USB stick while using a serial console can be a console baudrate mismatch. If a console variable is defined in u-boot, the &d-i; boot script automatically passes it to the kernel to set the primary console device and, if applicable, the console baudrate. Unfortunately the handling of the console variable varies from platform to platform - on some platforms, the console variable includes the baudrate (as in console=ttyS0,115200), while on other platforms the console variable contains only the device (as in console=ttyS0). The latter case leads to a garbled console output when the default baudrate differs between u-boot and the kernel. Modern u-boot versions often use 115200 baud while the kernel still defaults to the traditional 9600 baud. If this happens, you should manually set the console variable to contain the correct baudrate for your system and then start the installer with the run usb_boot command.