--- name: "mkdepthcharge" section: "1" platform: "linux" package: "depthcharge-tools" version: "0.6.2-2" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/mkdepthcharge" --- # mkdepthcharge(1) Build boot images for the ChromeOS bootloader ## NAME mkdepthcharge - Build boot images for the ChromeOS bootloader ## SYNOPSIS **mkdepthcharge** **-o** *FILE* \[options\] \[*VMLINUZ*\] \[*INITRAMFS* ...\] \[*DTB* ...\] ## DESCRIPTION **mkdepthcharge** wraps the [*mkimage*(1)](/mkimage/1.md) and [*vbutil\_kernel*(1)](/vbutil_kernel/1.md) programs with reasonable defaults to package its inputs into the format the ChromeOS bootloader expects. It also automates preprocessing steps and initramfs support hacks that a user would have to do manually or write a script for. The *VMLINUZ* should be a kernel executable, *INITRAMFS* should be a ramdisk image that the kernel should be able to use on its own, and *DTB* files should be device-tree binary files appropriate for the kernel. **mkdepthcharge** tries to determine the type of each input file by some heuristics on their contents, but failing that it assumes a file is whatever is missing in the *VMLINUZ*, *INITRAMFS*, *DTB* order. Alternatively, these files can be specified as options instead of positional arguments. ## OPTIONS ### Input files - **-d** *VMLINUZ,* **--vmlinuz** *VMLINUZ* Kernel executable. If a compressed file is given here, it is decompressed and its contents are used in its place. - **-i *INITRAMFS* \[*INITRAMFS* ...\], --initramfs *INITRAMFS* \[*INITRAMFS* ...\]** Ramdisk image. If multiple files are given (e.g. for CPU microcode updates), they are concatenated and used as a single file. - **-b *DTB* \[*DTB* ...\], --dtbs *DTB* \[*DTB* ...\]** Device-tree binary files. ### Global options - **-A** *ARCH,* **--arch** *ARCH* Architecture to build the images for. The following architectures are understood: **arm**, **arm64**, **aarch64** for ARM boards; **x86**, **x86\_64**, **amd64** for x86 boards. If not given, the build architecture of the *VMLINUZ* file is used. - **--format** *FORMAT* Kernel image format to use, either **fit** or **zimage**. If not given, architecture-specific defaults are used. - **fit** This is the default on ARM boards. The *VMLINUZ* and the optional *INITRAMFS*, *DTB* files are packaged into the Flattened Image Tree (FIT) format using [*mkimage*(1)](/mkimage/1.md) and that is passed to [*vbutil\_kernel*(1)](/vbutil_kernel/1.md). - **zimage** This is the default for x86 boards. The *VMLINUZ* is passed mostly unmodified to [*vbutil\_kernel*(1)](/vbutil_kernel/1.md), except for decompression and padding for self-decompression. The *INITRAMFS* file is passed as the **--bootloader** argument and the kernel header is modified to point to where it will be in memory. It does not support packaging *DTB* files. - **-h, --help** Show a help message and exit. - **--kernel-start** *ADDR* Start of the Depthcharge kernel buffer in memory. Depthcharge loads the packed data to a fixed physical address in memory, and some initramfs support hacks require this value to be known. This is exactly the board-specific **CONFIG\_KERNEL\_START** value in the Depthcharge source code and defaults to **0x100000** for the x86 architecture. - **-o** *FILE,* **--output** *FILE* Write the image to *FILE*. The image isn't generated at the output, but copied to it from a temporary working directory. This option is mandatory. - **--pad-vmlinuz, --no-pad-vmlinuz** Pad the *VMLINUZ* file so that the kernel's self-decompression has enough space to avoid overwriting the *INITRAMFS* file during boot. This has different defaults and behaviour depending on the image format, see explanations in their respective sections. - **--tmpdir** *DIR* Create and keep temporary files in *DIR*. If not given, a temporary **mkdepthcharge-\*** directory is created in **/tmp** and removed at exit. - **-v, --verbose** Print info messages, [*mkimage*(1)](/mkimage/1.md) output and [*vbutil\_kernel*(1)](/vbutil_kernel/1.md) output to stderr. - **-V, --version** Print program version and exit. ### FIT image options - **-C** *TYPE,* **--compress** *TYPE* Compress the *VMLINUZ* before packaging it into a FIT image, either with **lz4** or **lzma**. **none** is also accepted, but does nothing. - **-n** *DESC,* **--name** *DESC* Description of the *VMLINUZ* to put in the FIT image. - **--pad-vmlinuz, --no-pad-vmlinuz** Pad the *VMLINUZ* file so that the kernel's self-decompression has enough space to avoid overwriting the *INITRAMFS* file during boot. The necessary padding is calculated based on compressed and decompressed kernel sizes and the **--kernel-start** argument. On earliest boards U-Boot moves the *INITRAMFS* away to a safe place before running the *VMLINUZ*, and on ARM64 boards Depthcharge itself decompresses the *VMLINUZ* to a safe place. But 32-bit ARM boards with Depthcharge lack FIT ramdisk support and run the *VMLINUZ* in-place, so this initramfs support hack is necessary on those. This option is enabled by default when **--patch-dtbs** is given, use the **--no-pad-vmlinuz** argument to disable it. - **--patch-dtbs, --no-patch-dtbs** Add **linux,initrd-start** and **linux,initrd-end** properties to the *DTB* files' **/chosen** nodes. Their values are based on the **--kernel-start** or the **--ramdisk-load-address** argument, one of which is required if this argument is given. These properties are normally added by Depthcharge, but 32-bit ARM Chromebooks were released with versions before FIT ramdisk support was introduced, so this initramfs support hack is necessary on those. - **--ramdisk-load-address** *ADDR* Add a **load** property to the FIT ramdisk subimage section. The oldest ARM Chromebooks use an old custom U-Boot that implements the same verified boot flow as Depthcharge. Its FIT ramdisk support requires an explicit load address for the ramdisk, which can be provided with this argument. ### zImage image options - **--pad-vmlinuz, --no-pad-vmlinuz** Pad the *VMLINUZ* file so that the kernel's self-decompression has enough space to avoid overwriting the *INITRAMFS* file during boot. The necessary padding is calculated based on values in the zImage header and the **--kernel-start** argument. If the *VMLINUZ* and *INITRAMFS* are small enough (about 16 MiB in total) they may fit between **--kernel-start** and the start of the decompression buffer. In this case the padding is unnecessary and not added. The padding is usually larger than the decompressed version of the kernel, so it results in unbootable images for older boards with small image size limits. For these, it is usually necessary to use **--set-init-size**, or custom kernels to make the parts fit as described above. This is disabled by default in favour of **--set-init-size**, use the **--pad-vmlinuz** argument to enable it. - **--set-init-size, --no-set-init-size** Increase the **init\_size** kernel boot parameter so that the kernel's self-decompression does not overwrite the *INITRAMFS* file during boot. The modified value is calculated based on values in the zImage header and the **--kernel-start** argument. This only works if the kernel has **KASLR** enabled (as is the default), because then the kernel itself tries to avoid overwriting the *INITRAMFS* during decompression. However it does not do this when first copying the *VMLINUZ* to the end of the decompression buffer. Increasing **init\_size** shifts copy this upwards to avoid it overlapping *INITRAMFS*. If the *VMLINUZ* and *INITRAMFS* are small enough, they may fit before the first compressed copy's start. In this case changing the value is unnecessary and skipped. This is enabled by default, use the **--no-set-init-size** argument to disable it. ### Depthcharge image options - **--bootloader** *FILE* Bootloader stub for the very first Chromebooks that use H2C as their firmware. Beyond those, this field is ignored on the firmware side except as a ramdisk for the **multiboot** and **zbi** formats. If an *INITRAMFS* is given for the **zimage** format, it is placed here as part of an initramfs support hack for x86 boards. Otherwise, an empty file is used. - **-c *CMD* \[*CMD* ...\], --cmdline *CMD* \[*CMD* ...\]** Command-line parameters for the kernel. Can be used multiple times to append new values. If not given, **--** is used. The ChromeOS bootloader expands any instance of **%U** in the kernel command line with the PARTUUID of the ChromeOS kernel partition it has chosen to boot, e.g. **root=PARTUUID=%U/PARTNROFF=1** will set the root partition to the one after the booted partition. As knowing the currently booted partition is generally useful, **mkdepthcharge** prepends **kern\_guid=%U** to the given kernel command line parameters to capture it. Use **--no-kern-guid** to disable this. - **--kern-guid, --no-kern-guid** Prepend **kern\_guid=%U** to kernel command-line parameters. This is enabled by default, use the **--no-kern-guid** argument to disable it. - **--keydir** *KEYDIR* Directory containing verified boot keys to use. Equivalent to using **--keyblock** *KEYDIR*/**kernel.keyblock**, **--signprivate** *KEYDIR*/**kernel\_data\_key.vbprivk**, and **--signpubkey** *KEYDIR*/**kernel\_subkey.vbpubk**. - **--keyblock** *FILE,* **--signprivate** *FILE,* **--signpubkey** *FILE* ChromiumOS verified boot keys. More specifically: kernel key block, private keys in .vbprivk format, and public keys in .vbpubk format. If not given, defaults to files set in **depthcharge-tools** configuration. If those are not set, **mkdepthcharge** searches for these keys in **/etc/depthcharge-tools** and **/usr/share/vboot/devkeys** directories, the latter being test keys that may be distributed with [*vbutil\_kernel*(1)](/vbutil_kernel/1.md). You can set these in **depthcharge-tools** configuration by the **vboot-keyblock**, **vboot-private-key** and **vboot-public-key** options under a **depthcharge-tools** config section. ## EXIT STATUS In general, exits with zero on success and non-zero on failure. ## FILES - **/etc/depthcharge-tools/config, /etc/depthcharge-tools/config.d/*\**** The **depthcharge-tools** configuration files. These might be used to specify locations of the ChromiumOS verified boot keys as system configuration. - **/etc/depthcharge-tools** The **depthcharge-tools** configuration directory. **mkdepthcharge** searches this directory for verified boot keys. - **/usr/share/vboot/devkeys** A directory containing test keys which should have been installed by [*vbutil\_kernel*(1)](/vbutil_kernel/1.md). - ***KEYDIR*/kernel.keyblock** Default kernel key block file used for signing the image. - ***KEYDIR*/kernel\_subkey.vbpubk** Default public key used to verify signed images. - ***KEYDIR*/kernel\_data\_key.vbprivk** Default private key used for signing the image. ## EXAMPLES - **mkdepthcharge -o *depthcharge.img* */boot/vmlinuz*** The simplest invocation possible. If tried on an ARM board, the firmware might refuse to boot the output image since it doesn't have a dtb for the board. Otherwise, even if the firmware runs the */boot/vmlinuz* binary, it might not correctly boot due to non-firmware causes (e.g. kernel panic due to not having a root). - **mkdepthcharge -o *system.img* --cmdline *"root=/dev/mmcblk0p2"* --compress *lz4* -- */boot/vmlinuz.gz* */boot/initrd.img* *rk3399-gru-kevin.dtb*** A command someone using a Samsung Chromebook Plus (v1) might run on their board to create a bootable image for their running system. - **mkdepthcharge -o *veyron.img* -c *"root=LABEL=ROOT gpt"* --kernel-start *0x2000000* --patch-dtbs -- */boot/vmlinuz* */boot/initramfs-linux.img* */boot/dtbs/rk3288-veyron-\*.dtb*** Build an image intended to work on veyron boards like ASUS Chromebook C201PA and Chromebook Flip C100PA. The stock Depthcharge on these boards doesn't process the FIT ramdisk, so the dtbs needs to be patched to boot with initramfs. - **mkdepthcharge -o *peach-pit.img* -c *"console=null"* --ramdisk-load-address *0x44000000* -- *vmlinuz* *initramfs* *exynos5420-peach-pit.dtb* *exynos5420-peach-pit.dtb*** Build an image intended to work on a Samsung Chromebook 2 (11"). This board uses a custom U-Boot, so needs an explicit ramdisk load address. Its firmware has a bug with loading the device-tree file, so needs the file twice for the result to be actually bootable. ## SEE ALSO [*depthchargectl*(1)](/depthchargectl/1.md), [*mkimage*(1)](/mkimage/1.md), [*vbutil\_kernel*(1)](/vbutil_kernel/1.md), [*futility*(1)](/futility/1.md)