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