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ad57b98e21
Move this out of the main file since for simple users it is easier to rely on standard boot. Signed-off-by: Simon Glass <sjg@chromium.org> Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
277 lines
11 KiB
ReStructuredText
277 lines
11 KiB
ReStructuredText
Booting Ubuntu Manually
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-----------------------
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This shows a manual approach to booting Ubuntu without standard boot or the EFI
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interface.
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As an example of how to set up your boot flow with U-Boot, here are
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instructions for starting Ubuntu from U-Boot. These instructions have been
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tested on Minnowboard MAX with a SATA drive but are equally applicable on
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other platforms and other media. There are really only four steps and it's a
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very simple script, but a more detailed explanation is provided here for
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completeness.
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Note: It is possible to set up U-Boot to boot automatically using syslinux.
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It could also use the grub.cfg file (/efi/ubuntu/grub.cfg) to obtain the
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GUID. If you figure these out, please post patches to this README.
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Firstly, you will need Ubuntu installed on an available disk. It should be
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possible to make U-Boot start a USB start-up disk but for now let's assume
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that you used another boot loader to install Ubuntu.
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Use the U-Boot command line to find the UUID of the partition you want to
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boot. For example our disk is SCSI device 0::
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=> part list scsi 0
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Partition Map for SCSI device 0 -- Partition Type: EFI
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Part Start LBA End LBA Name
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Attributes
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Type GUID
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Partition GUID
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1 0x00000800 0x001007ff ""
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attrs: 0x0000000000000000
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type: c12a7328-f81f-11d2-ba4b-00a0c93ec93b
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guid: 9d02e8e4-4d59-408f-a9b0-fd497bc9291c
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2 0x00100800 0x037d8fff ""
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attrs: 0x0000000000000000
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type: 0fc63daf-8483-4772-8e79-3d69d8477de4
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guid: 965c59ee-1822-4326-90d2-b02446050059
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3 0x037d9000 0x03ba27ff ""
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attrs: 0x0000000000000000
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type: 0657fd6d-a4ab-43c4-84e5-0933c84b4f4f
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guid: 2c4282bd-1e82-4bcf-a5ff-51dedbf39f17
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=>
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This shows that your SCSI disk has three partitions. The really long hex
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strings are called Globally Unique Identifiers (GUIDs). You can look up the
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'type' ones `here`_. On this disk the first partition is for EFI and is in
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VFAT format (DOS/Windows)::
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=> fatls scsi 0:1
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efi/
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0 file(s), 1 dir(s)
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Partition 2 is 'Linux filesystem data' so that will be our root disk. It is
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in ext2 format::
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=> ext2ls scsi 0:2
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<DIR> 4096 .
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<DIR> 4096 ..
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<DIR> 16384 lost+found
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<DIR> 4096 boot
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<DIR> 12288 etc
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<DIR> 4096 media
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<DIR> 4096 bin
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<DIR> 4096 dev
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<DIR> 4096 home
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<DIR> 4096 lib
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<DIR> 4096 lib64
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<DIR> 4096 mnt
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<DIR> 4096 opt
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<DIR> 4096 proc
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<DIR> 4096 root
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<DIR> 4096 run
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<DIR> 12288 sbin
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<DIR> 4096 srv
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<DIR> 4096 sys
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<DIR> 4096 tmp
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<DIR> 4096 usr
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<DIR> 4096 var
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<SYM> 33 initrd.img
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<SYM> 30 vmlinuz
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<DIR> 4096 cdrom
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<SYM> 33 initrd.img.old
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=>
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and if you look in the /boot directory you will see the kernel::
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=> ext2ls scsi 0:2 /boot
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<DIR> 4096 .
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<DIR> 4096 ..
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<DIR> 4096 efi
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<DIR> 4096 grub
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3381262 System.map-3.13.0-32-generic
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1162712 abi-3.13.0-32-generic
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165611 config-3.13.0-32-generic
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176500 memtest86+.bin
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178176 memtest86+.elf
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178680 memtest86+_multiboot.bin
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5798112 vmlinuz-3.13.0-32-generic
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165762 config-3.13.0-58-generic
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1165129 abi-3.13.0-58-generic
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5823136 vmlinuz-3.13.0-58-generic
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19215259 initrd.img-3.13.0-58-generic
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3391763 System.map-3.13.0-58-generic
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5825048 vmlinuz-3.13.0-58-generic.efi.signed
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28304443 initrd.img-3.13.0-32-generic
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=>
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The 'vmlinuz' files contain a packaged Linux kernel. The format is a kind of
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self-extracting compressed file mixed with some 'setup' configuration data.
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Despite its size (uncompressed it is >10MB) this only includes a basic set of
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device drivers, enough to boot on most hardware types.
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The 'initrd' files contain a RAM disk. This is something that can be loaded
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into RAM and will appear to Linux like a disk. Ubuntu uses this to hold lots
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of drivers for whatever hardware you might have. It is loaded before the
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real root disk is accessed.
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The numbers after the end of each file are the version. Here it is Linux
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version 3.13. You can find the source code for this in the Linux tree with
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the tag v3.13. The '.0' allows for additional Linux releases to fix problems,
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but normally this is not needed. The '-58' is used by Ubuntu. Each time they
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release a new kernel they increment this number. New Ubuntu versions might
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include kernel patches to fix reported bugs. Stable kernels can exist for
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some years so this number can get quite high.
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The '.efi.signed' kernel is signed for EFI's secure boot. U-Boot has its own
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secure boot mechanism - see `this`_ & `that`_. It cannot read .efi files
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at present.
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To boot Ubuntu from U-Boot the steps are as follows:
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1. Set up the boot arguments. Use the GUID for the partition you want to boot::
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=> setenv bootargs root=/dev/disk/by-partuuid/965c59ee-1822-4326-90d2-b02446050059 ro
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Here root= tells Linux the location of its root disk. The disk is specified
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by its GUID, using '/dev/disk/by-partuuid/', a Linux path to a 'directory'
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containing all the GUIDs Linux has found. When it starts up, there will be a
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file in that directory with this name in it. It is also possible to use a
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device name here, see later.
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2. Load the kernel. Since it is an ext2/4 filesystem we can do::
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=> ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic
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The address 30000000 is arbitrary, but there seem to be problems with using
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small addresses (sometimes Linux cannot find the ramdisk). This is 48MB into
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the start of RAM (which is at 0 on x86).
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3. Load the ramdisk (to 64MB)::
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=> ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic
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4. Start up the kernel. We need to know the size of the ramdisk, but can use
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a variable for that. U-Boot sets 'filesize' to the size of the last file it
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loaded::
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=> zboot 03000000 0 04000000 ${filesize}
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Type 'help zboot' if you want to see what the arguments are. U-Boot on x86 is
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quite verbose when it boots a kernel. You should see these messages from
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U-Boot::
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Valid Boot Flag
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Setup Size = 0x00004400
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Magic signature found
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Using boot protocol version 2.0c
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Linux kernel version 3.13.0-58-generic (buildd@allspice) #97-Ubuntu SMP Wed Jul 8 02:56:15 UTC 2015
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Building boot_params at 0x00090000
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Loading bzImage at address 100000 (5805728 bytes)
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Magic signature found
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Initial RAM disk at linear address 0x04000000, size 19215259 bytes
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Kernel command line: "root=/dev/disk/by-partuuid/965c59ee-1822-4326-90d2-b02446050059 ro"
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Starting kernel ...
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U-Boot prints out some bootstage timing. This is more useful if you put the
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above commands into a script since then it will be faster::
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Timer summary in microseconds:
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Mark Elapsed Stage
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0 0 reset
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241,535 241,535 board_init_r
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2,421,611 2,180,076 id=64
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2,421,790 179 id=65
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2,428,215 6,425 main_loop
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48,860,584 46,432,369 start_kernel
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Accumulated time:
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240,329 ahci
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1,422,704 vesa display
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Now the kernel actually starts (if you want to examine kernel boot up message on
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the serial console, append "console=ttyS0,115200" to the kernel command line)::
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[ 0.000000] Initializing cgroup subsys cpuset
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[ 0.000000] Initializing cgroup subsys cpu
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[ 0.000000] Initializing cgroup subsys cpuacct
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[ 0.000000] Linux version 3.13.0-58-generic (buildd@allspice) (gcc version 4.8.2 (Ubuntu 4.8.2-19ubuntu1) ) #97-Ubuntu SMP Wed Jul 8 02:56:15 UTC 2015 (Ubuntu 3.13.0-58.97-generic 3.13.11-ckt22)
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[ 0.000000] Command line: root=/dev/disk/by-partuuid/965c59ee-1822-4326-90d2-b02446050059 ro console=ttyS0,115200
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It continues for a long time. Along the way you will see it pick up your
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ramdisk::
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[ 0.000000] RAMDISK: [mem 0x04000000-0x05253fff]
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...
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[ 0.788540] Trying to unpack rootfs image as initramfs...
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[ 1.540111] Freeing initrd memory: 18768K (ffff880004000000 - ffff880005254000)
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...
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Later it actually starts using it::
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Begin: Running /scripts/local-premount ... done.
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You should also see your boot disk turn up::
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[ 4.357243] scsi 1:0:0:0: Direct-Access ATA ADATA SP310 5.2 PQ: 0 ANSI: 5
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[ 4.366860] sd 1:0:0:0: [sda] 62533296 512-byte logical blocks: (32.0 GB/29.8 GiB)
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[ 4.375677] sd 1:0:0:0: Attached scsi generic sg0 type 0
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[ 4.381859] sd 1:0:0:0: [sda] Write Protect is off
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[ 4.387452] sd 1:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
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[ 4.399535] sda: sda1 sda2 sda3
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Linux has found the three partitions (sda1-3). Mercifully it doesn't print out
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the GUIDs. In step 1 above we could have used::
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setenv bootargs root=/dev/sda2 ro
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instead of the GUID. However if you add another drive to your board the
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numbering may change whereas the GUIDs will not. So if your boot partition
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becomes sdb2, it will still boot. For embedded systems where you just want to
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boot the first disk, you have that option.
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The last thing you will see on the console is mention of plymouth (which
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displays the Ubuntu start-up screen) and a lot of 'Starting' messages::
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* Starting Mount filesystems on boot [ OK ]
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After a pause you should see a login screen on your display and you are done.
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If you want to put this in a script you can use something like this::
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setenv bootargs root=UUID=b2aaf743-0418-4d90-94cc-3e6108d7d968 ro
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setenv boot zboot 03000000 0 04000000 \${filesize}
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setenv bootcmd "ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic; ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic; run boot"
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saveenv
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The \ is to tell the shell not to evaluate ${filesize} as part of the setenv
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command.
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You can also bake this behaviour into your build by hard-coding the
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environment variables if you add this to minnowmax.h:
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.. code-block:: c
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#undef CONFIG_BOOTCOMMAND
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#define CONFIG_BOOTCOMMAND \
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"ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic; " \
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"ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic; " \
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"run boot"
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#undef CFG_EXTRA_ENV_SETTINGS
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#define CFG_EXTRA_ENV_SETTINGS "boot=zboot 03000000 0 04000000 ${filesize}"
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and change CONFIG_BOOTARGS value in configs/minnowmax_defconfig to::
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CONFIG_BOOTARGS="root=/dev/sda2 ro"
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.. _here: https://en.wikipedia.org/wiki/GUID_Partition_Table
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.. _this: http://events.linuxfoundation.org/sites/events/files/slides/chromeos_and_diy_vboot_0.pdf
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.. _that: http://events.linuxfoundation.org/sites/events/files/slides/elce-2014.pdf
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