bootm command

Synopsis

bootm [start|restart] [<fit_addr>]#<conf>[#<extra-conf>]
bootm [start|restart] [[<fit_addr>]:<os_subimg>] [[<fit_addr2>]:<rd_subimg2>] [[<fit_addr3>]:<fdt_subimg>]
bootm <subcmd>

bootm <addr1> [[<addr2> [<addr3>]]    # Legacy boot

Description

The bootm command is used to boot an Operating System. It has a large number of options depending on what needs to be booted.

Note that the second form supports the first and/or second arguments to be omitted by using a hyphen ‘-’ instead.

fit_addr / fit_addr2 / fit_addr3

address of FIT to boot, defaults to CONFIG_SYS_LOAD_ADDR. See notes below.

conf

configuration unit to boot (must be preceded by hash ‘#’)

extra-conf

extra configuration to boot. This is supported only for additional devicetree overlays to apply on the base device tree supplied by the first configuration unit.

os_subimg

OS sub-image to boot (must be preceded by colon ‘:’)

rd_subimg

ramdisk sub-image to boot. Use a hyphen ‘-’ if there is no ramdisk but an FDT is needed.

fdt_subimg

FDT sub-image to boot

Bootm steps

The bootm command follows a predefined set of states to complete a boot. The usual case, if a subcommand is omitted, is that bootm runs a complete boot, working through each state one by one, in sequence. Some states are skipped depending on the boot type.

Note that the bootm command automatically adds findos and findother states when the start state begins. These states are documented here but cannot be individually selected.

The states are described below:

start

Start the boot process afresh, recording the image(s) to be booted.

restart

Start the boot process again, but keeping the current state. This allows multiple FITs to be loaded, for example a first FIT containing just the devicetree and a second containing the OS and any overlays. In this case, the first bootm command will typically use only start (and its implicit states) and loados, with the second using bootm restart to select the second FIT.

preload

Deal with any preload step, sometimes used to do a full signature check of the FIT, before looking at any of the data within.

This cannot be selected from the bootm command, as it is implicit in start.

findos

Find the OS within the FIT, etc. and set up the images.os fields

This cannot be selected from the bootm command, as it is implicit in start.

findother

Find other files that may be needed, including any ramdisk, devicetree, FPGA or loadables. After this, the images.rd… and images.ft fields are set up.

For each loadable, the appropriate handler is called (as declared by the U_BOOT_FIT_LOADABLE_HANDLER() macro). There is no record kept of which loadables were loaded, other than that used by Universal Payload.

This step is only active if the image type is kernel, kernel_noload or multi, and the OS is Linux, VxWorks, EFI or TEE.

This cannot be selected from the bootm command, as it is implicit in start.

measure

This measures the loaded files, if CONFIG_MEASURED_BOOT is enabled.

This cannot be selected from the bootm command. Currently it is only used when using bootm without a subcommand.

loados

Load the OS itself to its final location. This may involve copying or decompressing it.

ramdisk

Load the ramdisk to its final location, if necessary. This typically involves copying it out of the FIT.

fdt

Load the devicetree to its final location. This typically involves copying or decompressing it from the FIT.

cmdline

Set up the command line for the OS, e.g. using the bootargs environment variable, perhaps adding some more pieces from an extlinux.conf entry.

bdt

Set up the board information for the OS (seldom used these days).

prep

Prepare to boot the OS, e.g. setting up any tables or data structures that are required. After this the OS itself is ready to boot.

fake

This is only used for testing and only available when CONFIG_BOOTM_FAKE_GO is enabled. It fakes a boot of the OS, performs all the normal steps right up to the point where U-Boot is about to jump to the OS. It then runs a list of commands from the fakegocmd environment variable. Note that the machine may not be stable after this occurs.

This can be useful for debugging slow booting, for example. See Tracing in U-Boot for more details.

go

Start the OS, after performing any last-minute tasks. At this point, the OS should be running and U-Boot’s task is completed.

Subcommands

Except as noted above, it is possible to perform the bootm processing piecemeal. The first command must be bootm start after which the others can be used, normally in the order they are documented above. This can aid debugging but it can also help to see what happens at each stage and the state of U-Boot and memory after each stage.

See below for legacy boot. Booting using Flat Image Tree (FIT) is recommended.

Note on current image address

When bootm is called without arguments, the image at current image address is booted. The current image address is the address set most recently by a load command, etc, and is by default equal to CONFIG_SYS_LOAD_ADDR. For example, consider the following commands:

tftp 200000 /tftpboot/kernel
bootm
# Last command is equivalent to:
# bootm 200000

As shown above, with FIT the address portion of any argument can be omitted. If <addr3> is omitted, then it is assumed that image at <addr2> should be used. Similarly, when <addr2> is omitted, it is assumed that image at <addr1> should be used. If <addr1> is omitted, it is assumed that the current image address is to be used. For example, consider the following commands:

tftp 200000 /tftpboot/uImage
bootm :kernel-1
# Last command is equivalent to:
# bootm 200000:kernel-1

tftp 200000 /tftpboot/uImage
bootm 400000:kernel-1 :ramdisk-1
# Last command is equivalent to:
# bootm 400000:kernel-1 400000:ramdisk-1

tftp 200000 /tftpboot/uImage
bootm :kernel-1 400000:ramdisk-1 :fdt-1
# Last command is equivalent to:
# bootm 200000:kernel-1 400000:ramdisk-1 400000:fdt-1

Legacy boot

U-Boot supports a legacy image format, enabled by CONFIG_LEGACY_IMAGE_FORMAT. This is not recommended as it is quite limited and insecure. Use Flat Image Tree (FIT) instead. It is documented here for old boards which still use it.

Arguments are:

addr1

address of legacy image to boot. If the image includes a second component (ramdisk) it is used as well, unless the second parameter is hyphen ‘-‘.

addr2

address of legacy image to use as ramdisk

addr3

address of legacy image to use as FDT

Example syntax

This section provides various examples of possible usage:

1.  bootm       /* boot image at the current address, equivalent to 2,3,8 */

This is equivalent to cases 2, 3 or 8, depending on the type of image at the current image address.

Boot method: see cases 2,3,8

Legacy uImage syntax

2.  bootm <addr1>            /* single image at <addr1> */

Boot kernel image located at <addr1>.

Boot method: non-FDT

3.  bootm <addr1>            /* multi-image at <addr1>  */

First and second components of the image at <addr1> are assumed to be a kernel and a ramdisk, respectively. The kernel is booted with initrd loaded with the ramdisk from the image.

Boot method: depends on the number of components at <addr1>, and on whether U-Boot is compiled with OF support, which it should be.

Configuration	2 components (kernel, initrd)	3 components (kernel, initrd, fdt)
#ifdef CONFIG_OF_*	non-FDT	FDT
#ifndef CONFIG_OF_*	non-FDT	non-FDT

4.  bootm <addr1> -            /* multi-image at <addr1>  */

Similar to case 3, but the kernel is booted without initrd. Second component of the multi-image is irrelevant (it can be a dummy, 1-byte file).

Boot method: see case 3

5.  bootm <addr1> <addr2>        /* single image at <addr1> */

Boot kernel image located at <addr1> with initrd loaded with ramdisk from the image at <addr2>.

Boot method: non-FDT

6.  bootm <addr1> <addr2> <addr3>   /* single image at <addr1> */

<addr1> is the address of a kernel image, <addr2> is the address of a ramdisk image, and <addr3> is the address of a FDT binary blob. Kernel is booted with initrd loaded with ramdisk from the image at <addr2>.

Boot method: FDT

7.  bootm <addr1> -      <addr3>   /* single image at <addr1> */

<addr1> is the address of a kernel image and <addr3> is the address of a FDT binary blob. Kernel is booted without initrd.

Boot method: FDT

FIT syntax

8.  bootm <addr1>

Image at <addr1> is assumed to contain a default configuration, which is booted.

Boot method: FDT or non-FDT, depending on whether the default configuration defines FDT

9.  bootm [<addr1>]:<subimg1>

Similar to case 2: boot kernel stored in <subimg1> from the image at address <addr1>.

Boot method: non-FDT

10. bootm [<addr1>]#<conf>[#<extra-conf[#...]]

Boot configuration <conf> from the image at <addr1>.

Boot method: FDT or non-FDT, depending on whether the configuration given defines FDT

11. bootm [<addr1>]:<subimg1> [<addr2>]:<subimg2>

Equivalent to case 5: boot kernel stored in <subimg1> from the image at <addr1> with initrd loaded with ramdisk <subimg2> from the image at <addr2>.

Boot method: non-FDT

12. bootm [<addr1>]:<subimg1> [<addr2>]:<subimg2> [<addr3>]:<subimg3>

Equivalent to case 6: boot kernel stored in <subimg1> from the image at <addr1> with initrd loaded with ramdisk <subimg2> from the image at <addr2>, and pass FDT blob <subimg3> from the image at <addr3>.

Boot method: FDT

13. bootm [<addr1>]:<subimg1> [<addr2>]:<subimg2> <addr3>

Similar to case 12, the difference being that <addr3> is the address of FDT binary blob that is to be passed to the kernel.

Boot method: FDT

14. bootm [<addr1>]:<subimg1> -              [<addr3>]:<subimg3>

Equivalent to case 7: boot kernel stored in <subimg1> from the image at <addr1>, without initrd, and pass FDT blob <subimg3> from the image at <addr3>.

Boot method: FDT

15. bootm [<addr1>]:<subimg1> - <addr3>

Similar to case 14, the difference being that <addr3> is the address of the FDT binary blob that is to be passed to the kernel.

Boot method: FDT

Example

boot kernel “kernel-1” stored in a new uImage located at 200000:

bootm 200000:kernel-1

boot configuration “cfg-1” from a new uImage located at 200000:

bootm 200000#cfg-1

boot configuration “cfg-1” with extra “cfg-2” from a new uImage located at 200000:

bootm 200000#cfg-1#cfg-2

boot “kernel-1” from a new uImage at 200000 with initrd “ramdisk-2” found in some other new uImage stored at address 800000:

bootm 200000:kernel-1 800000:ramdisk-2

boot “kernel-2” from a new uImage at 200000, with initrd “ramdisk-1” and FDT “fdt-1”, both stored in some other new uImage located at 800000:

bootm 200000:kernel-1 800000:ramdisk-1 800000:fdt-1

boot kernel “kernel-2” with initrd “ramdisk-2”, both stored in a new uImage at address 200000, with a raw FDT blob stored at address 600000:

bootm 200000:kernel-2 200000:ramdisk-2 600000

boot kernel “kernel-2” from new uImage at 200000 with FDT “fdt-1” from the same new uImage:

bootm 200000:kernel-2 - 200000:fdt-1