.. _booting_linux: Booting Linux ============= Introduction ------------ The basic boot command in barebox is :ref:`command_bootm`. This command can be used directly, but there is also a :ref:`command_boot` command which offers additional features like a boot sequence which tries to boot different entries until one succeeds. The bootm command ----------------- The :ref:`command_bootm` command is the basic boot command. Depending on the architecture the bootm command handles different image types. On ARM the following images are supported: * ARM Linux zImage * U-Boot uImage * barebox images The images can either be passed directly to the bootm command as argument or in the ``global.bootm.image`` variable: .. code-block:: sh bootm /path/to/zImage # same as: global.bootm.image=/path/to/zImage bootm When barebox has an internal devicetree it is passed to the kernel. You can specify an alternative devicetree with the ``-o DTS`` option or the ``global.bootm.oftree`` variable: .. code-block:: sh bootm -o /path/to/dtb /path/to/zImage # same as: global.bootm.oftree=/path/to/dtb global.bootm.image=/path/to/zImage bootm **NOTE:** it may happen that barebox is probed from the devicetree, but you have want to start a Kernel without passing a devicetree. In this case call ``oftree -f`` to free the internal devicetree before calling ``bootm`` Passing Kernel Arguments ^^^^^^^^^^^^^^^^^^^^^^^^ The simple method to pass bootargs to the kernel is with ``CONFIG_FLEXIBLE_BOOTARGS`` disabled: in this case the bootm command takes the bootargs from the ``bootargs`` environment variable. With ``CONFIG_FLEXIBLE_BOOTARGS`` enabled, the bootargs are composed from different :ref:`global device` variables. All variables beginning with ``global.linux.bootargs.`` will be concatenated to the bootargs: .. code-block:: sh global linux.bootargs.base="console=ttyO0,115200" global linux.bootargs.debug="earlyprintk ignore_loglevel" bootm zImage ... Kernel command line: console=ttymxc0,115200n8 earlyprintk ignore_loglevel Additionally all variables starting with ``global.linux.mtdparts.`` are concatenated to a ``mtdparts=`` parameter to the kernel. This makes it possible to consistently partition devices with the :ref:`command_addpart` command and pass the same string as used with addpart to the Kernel: .. code-block:: sh norparts="512k(bootloader),512k(env),4M(kernel),-(root)" nandparts="1M(bootloader),1M(env),4M(kernel),-(root)" global linux.mtdparts.nor0="physmap-flash.0:$norparts" global linux.mtdparts.nand0="mxc_nand:$nandparts" addpart /dev/nor0 $norparts addpart /dev/nand0 $nandparts ... bootm zImage ... Kernel command line: mtdparts=physmap-flash.0:512k(bootloader),512k(env),4M(kernel),-(root); mxc_nand:1M(bootloader),1M(env),4M(kernel),-(root) The boot command ---------------- The :ref:`command_boot` command offers additional convenience for the :ref:`command_bootm` command. It works with :ref:`boot_entries` and :ref:`bootloader_spec` entries. Boot entries are located under /env/boot/ and are scripts which setup the bootm variables so that the ``boot`` command can run ``bootm`` without further arguments. .. _boot_entries: Boot entries ^^^^^^^^^^^^ A simple boot entry in ``/env/boot/mmc`` could look like this: .. code-block:: sh #!/bin/sh global.bootm.image=/mnt/mmc1/zImage global.bootm.oftree=/env/oftree global linux.bootargs.dyn.root="root=PARTUUID=deadbeef:01" This takes the kernel from ``/mnt/mmc1/zImage`` (which could be an :ref:`automount` path registered earlier). The devicetree will be used from ``/env/oftree``. The Kernel gets the command line ``root=PARTUUID=deadbeef:01``. Note the ``.dyn`` in the bootargs variable name. boot entries should always add Kernel command line parameters to variables with ``.dyn`` in it. These will be cleared before booting different boot entries. This is done so that following boot entries do not leak command line parameters from the previous boot entries. This entry can be booted with ``boot mmc``. It can also be made the default by setting the ``global.boot.default`` variable to ``mmc`` and then calling ``boot`` without arguments. .. _bootloader_spec: Bootloader Spec ^^^^^^^^^^^^^^^ barebox supports booting according to the bootloader spec: http://www.freedesktop.org/wiki/Specifications/BootLoaderSpec/ It follows another philosophy than the :ref:`boot_entries`. With Boot Entries booting is completely configured in the bootloader. Bootloader Spec Entries on the other hand the boot entries are on a boot medium. This gives a boot medium the possibility to describe where a Kernel is and what parameters it needs. All Bootloader Spec Entries are in a partition on the boot medium under ``/loader/entries/*.conf``. In the Bootloader Spec a boot medium has a dedicated partition to use for boot entries. barebox is less strict, it accepts Bootloader Spec Entries on every partition barebox can read. A Bootloader Spec Entry consists of key value pairs:: /loader/entries/6a9857a393724b7a981ebb5b8495b9ea-3.8.0-2.fc19.x86_64.conf: title Fedora 19 (Rawhide) version 3.8.0-2.fc19.x86_64 machine-id 6a9857a393724b7a981ebb5b8495b9ea options root=UUID=6d3376e4-fc93-4509-95ec-a21d68011da2 linux /6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.x86_64/linux initrd /6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.x86_64/initrd All paths are absolute paths in the partition. Bootloader Spec Entries can be created manually, but there also is the ``scripts/kernel-install`` tool to create/list/modify entries directly on a MMC/SD card or other media. To use it create a SD card / USB memory stick with a /boot partition with type 0xea. The partition can be formatted with FAT or EXT4 filesystem. If you wish to write to it from barebox later you must use FAT. The following creates a Bootloader Spec Entry on a SD card: .. code-block:: sh scripts/kernel-install --device=/dev/mmcblk0 -a \ --machine-id=11ab7c89d02c4f66a4e2474ea25b2b84 --kernel-version="3.15" \ --kernel=/home/sha/linux/arch/arm/boot/zImage --add-root-option \ --root=/dev/mmcblk0p1 -o "console=ttymxc0,115200" The entry can be listed with the -l option: .. code-block:: sh scripts/kernel-install --device=/dev/mmcblk0 -l Entry 0: title: Linux-3.15 version: 3.15 machine_id: 11ab7c89d02c4f66a4e2474ea25b2b84 options: console=ttymxc0,115200 root=PARTUUID=0007CB20-01 linux: 11ab7c89d02c4f66a4e2474ea25b2b84.15/linux When on barebox the SD card shows up as ``mmc1`` then this entry can be booted with ``boot mmc1`` or with setting ``global.boot.default`` to ``mmc1``. A bootloader spec entry can also reside on an NFS server in which case a RFC2224 compatible NFS URI string must be passed to the boot command: .. code-block:: sh boot nfs://nfshost//path/ Additionally to the options defined in the original spec barebox understands the ``linux-appendroot`` option. This is a boolean value and if set to ``true`` barebox will automatically append a ``root=`` string to the Linux commandline based on the device where the entry is found on. This makes it possible to use the same rootfs image on different devices without having to specify a different root= option each time. Network boot ------------ With the following steps barebox can start the Kernel and root filesystem over network, a standard development case. Configure network: edit ``/env/network/eth0``. For a standard dhcp setup the following is enough: .. code-block:: sh #!/bin/sh ip=dhcp serverip=192.168.23.45 serverip is only necessary if it differs from the serverip offered from the dhcp server. A static ip setup can look like this: .. code-block:: sh #!/bin/sh ip=static ipaddr=192.168.2.10 netmask=255.255.0.0 gateway=192.168.2.1 serverip=192.168.2.1 Note that barebox will pass the same ip settings to the kernel, i.e. it passes ``ip=$ipaddr:$serverip:$gateway:$netmask::eth0:`` for a static ip setup and ``ip=dhcp`` for a dynamic dhcp setup. Adjust ``global.user`` and maybe ``global.hostname`` in ``/env/config``:: global.user=sha global.hostname=efikasb Copy the kernel (and devicetree if needed) to the base dir of the TFTP server:: cp zImage /tftpboot/sha-linux-efikasb cp myboard.dtb /tftpboot/sha-oftree-efikasb barebox will pass ``nfsroot=/home/${global.user}/nfsroot/${global.hostname}`` This may be a link to another location on the NFS server. Make sure that the link target is exported from the server. ``boot net`` will then start the Kernel. If the paths or names are not suitable they can be adjusted in ``/env/boot/net``: .. code-block:: sh #!/bin/sh path="/mnt/tftp" global.bootm.image="${path}/${global.user}-linux-${global.hostname}" oftree="${path}/${global.user}-oftree-${global.hostname}" if [ -f "${oftree}" ]; then global.bootm.oftree="$oftree" fi nfsroot="/home/${global.user}/nfsroot/${global.hostname}" bootargs-ip global.linux.bootargs.dyn.root="root=/dev/nfs nfsroot=$nfsroot,v3,tcp"