This section provides a reference of variables Mender use during the Yocto Project build process. The variables are either specific to- and defined by Mender, as shown by the MENDER_ prefix, or defined by the Yocto Project and used by Mender.

ARTIFACTIMG_FSTYPE

Value: ext4 (default) / <filesystem type>

Defines which filesystem type Mender will build for the rootfs partitions in the .biosimg, .sdimg, .uefiimg and the .mender file. See filesystem types for more information.

ARTIFACTIMG_NAME

Value: <any string> (defaults to image filename)

Overrides the default internal image name that mender will use to build the .mender file with.

IMAGE_ROOTFS_SIZE

Value: <size in KiB> (default calculated from several factors, see below)

The size of the generated rootfs, expressed in kiB. This will be the size of the rootfs image shipped in a .mender update. This variable is a standard Yocto Project variable influenced by several other factors. See the Yocto Project documentation for more information.

Note that this variable has no effect when generating a complete disk image (any suffix ending in img), since meta-mender will determine the size automatically in this case. See MENDER_STORAGE_TOTAL_SIZE_MB for more information.

It is recommended not to set this variable, but instead set MENDER_STORAGE_TOTAL_SIZE_MB and let meta-mender set IMAGE_ROOTFS_SIZE from that variable automatically.

MENDER_ARTIFACT_EXTRA_ARGS

Value: <mender artifact arguments> (default: empty)

Flags added to this variable will be used as extra arguments to the mender-artifact tool when creating the .mender artifact. For example:

MENDER_ARTIFACT_EXTRA_ARGS:append = " -v 1"

The above example builds an artifact with the version 1 format.

MENDER_ARTIFACT_NAME

Value: <name of artifact> (no default, required)

The name of the image or update that will be built. This is what the device will report that it is running, and different updates must have different names. This variable must be defined or the build will fail.

MENDER_ARTIFACT_SIGNING_KEY

Value: <key used to sign artifact> (default: empty)

Optional path to a private key used to sign the update artifact. The default is empty, which means the artifact won't be signed.

The signature can also be added or changed outside the build process, by using the mender-artifact tool's -k option. For more information, see signing Mender Artifacts.

MENDER_ARTIFACT_VERIFY_KEY

Value: <key used to verify artifact> (default: empty)

If set, this will add the given public verification key to the client configuration, which means that the client will reject updates which are not signed by the corresponding private key (see MENDER_ARTIFACT_SIGNING_KEY).

More specifically, it will add the key to the root filesystem under /etc/mender/artifact-verify-key.pem, and add a ArtifactVerifyKey entry to mender.conf, pointing to this key. Using MENDER_ARTIFACT_VERIFY_KEY is recommended when the key is hosted in a file external to the build system / Yocto Project layer.

An alternative way to specify a verification key is to include a file named artifact-verify-key.pem in SRC_URI. This is a better approach if the key is hosted inside a Yocto Project layer, as opposed to living externally on the local host somewhere. Otherwise it has the same effect as defining MENDER_ARTIFACT_VERIFY_KEY.

Note that you cannot both use MENDER_ARTIFACT_VERIFY_KEY and have artifact-verify-key.pem in SRC_URI at the same time.

MENDER_BOOT_PART

Value: <block device> (default: 1st partition on MENDER_STORAGE_DEVICE)

The partition Mender uses as the boot partition. See More detailed storage configuration for more information.

MENDER_BOOT_PART_FSTYPE

Value: auto (default) / <filesystem type>

Filesystem type of boot partition. This configuration is only used in fstab. Most filesystems can be auto detected, but some can not and hence this variable exists to override the auto detection.

MENDER_BOOT_PART_SIZE_MB

Value: 16 (default)

The size of the boot partition in the generated .biosimg, .sdimg or .uefiimg file. See Configuring the partition sizes for more information.

MENDER_DATA_PART

Value: <block device> (default: 4th partition on MENDER_STORAGE_DEVICE)

The partition Mender uses as the persistent data partition. See More detailed storage configuration for more information.

MENDER_DATA_PART_FSTYPE

Value: auto (default) / <filesystem type>

Filesystem type of data partition. This configuration is only used in fstab. Most filesystems can be auto detected, but some can not and hence this variable exists to override the auto detection.

MENDER_DATA_PART_SIZE_MB

Value: 128 (default)

The size of the persistent data partition in the generated .biosimg, .sdimg or .uefiimg file. See Configuring the partition sizes for more information.

MENDER_DEMO_HOST_IP_ADDRESS

Value: <IP address> (default: empty)

As the name indicates, this variable is only relevant if you are building Mender with the meta-mender-demo layer. If set to an IP address, this variable sets the hostname resolution of the API gateway and the storage proxy (docker.mender.io and s3.docker.mender.io) to that address. The default is empty, which reverts to querying DNS (but note that the Docker setup comes with its own DNS server).

MENDER_DEVICE_TYPE

Value: <any string> (default: value of ${MACHINE})

A string that defines the type of the target device for this image. This variable is only relevant when building a complete partitioned image (any suffix ending in img). Once flashed with this image, the device type will persist across subsequent updates.

MENDER_DEVICE_TYPES_COMPATIBLE

Value: <strings> (default: value of ${MACHINE})

A space separated string of device types that determine which types of devices this update is suitable for. This complements the MENDER_DEVICE_TYPE variable, and is only relevant when building a .mender update, not when building a partitioned image (any suffix ending in img).

MENDER_EXTRA_PARTS

Value: <Extra partitions list> (default: empty)

This variable defines extra partitions which will be added after the data partition. MENDER_EXTRA_PARTS_SIZES_MB and MENDER_EXTRA_PARTS_FSTAB can be used to further tweak the partition setup. For example:

MENDER_EXTRA_PARTS = "part1 part2"
MENDER_EXTRA_PARTS[part1] = "--label=static --fstype=ext4"
MENDER_EXTRA_PARTS[part2] = "--label=update --fstype=vfat"
# Size (in MB) of specified extra partition
MENDER_EXTRA_PARTS_SIZES_MB[part1] = "64"
MENDER_EXTRA_PARTS_SIZES_MB[part2] = "128"
# FSTAB options of specified extra partition (optional)
MENDER_EXTRA_PARTS_FSTAB[part1] = "ext4 noexec 0 0"
MENDER_EXTRA_PARTS_FSTAB[part2] = "vfat ro,user 0 0"

Arguments are passed as is to wks file and used by the wic tool

See also MENDER_EXTRA_PARTS_FSTAB and MENDER_EXTRA_PARTS_SIZES_MB.

MENDER_EXTRA_PARTS_FSTAB

Value: <List of fstab mount options for extra partitions> (default: empty)

The mount options for /etc/fstab of the extra partitions defined by MENDER_EXTRA_PARTS in the generated .biosimg, .sdimg or .uefiimg file.

MENDER_EXTRA_PARTS_FSTAB[part1] = "ext4 noexec 0 0"
MENDER_EXTRA_PARTS_FSTAB[part2] = "vfat ro,user 0 0"

See MENDER_EXTRA_PARTS.

MENDER_EXTRA_PARTS_SIZES_MB

Value: <Extra partitions size list> (default: empty)

The size of the extra partitions defined by MENDER_EXTRA_PARTS in the generated .biosimg, .sdimg or .uefiimg file.

If defined, --fixed-size will automatically be added to the wks file and used by the wic tool

MENDER_EXTRA_PARTS_SIZES_MB[part1] = "1024"
MENDER_EXTRA_PARTS_SIZES_MB[part2] = "9216"

See MENDER_EXTRA_PARTS.

MENDER_FEATURES_DISABLE

Value: <mender features> (default: empty)

Disable Mender features by appending to this variable. See the section on features for more information.

MENDER_FEATURES_ENABLE

Value: <mender features> (default: platform dependent)

Enable Mender features by appending to this variable. See the section on features for more information.

MENDER_IMAGE_BOOTLOADER_BOOTSECTOR_OFFSET

Value: <sector number> (default: platform dependent)

Together with MENDER_IMAGE_BOOTLOADER_FILE, this sets the offset for placing the bootloader, counting from the start of the storage medium. The offset is specified in units of 512-byte sectors. The value needs to be non-zero, or the partition table itself would be overwritten.

MENDER_IMAGE_BOOTLOADER_FILE

Value: <bootloader filename> (default: platform dependent)

Together with MENDER_IMAGE_BOOTLOADER_BOOTSECTOR_OFFSET, this specifies a file that you would like to write directly into the boot sector, in the intervening space between the partition table and the first partition.

MENDER_IS_ON_MTDID

Value: <MTD ID> (default: first MTD ID in MENDER_MTDIDS)

This variable is only relevant if the the mender-ubi feature is enabled. The variable should be set to the MTDID of the device that mender, and the root filesystem in particular, resides on. Setting this variable is usually done automatically, but some cases require setting it manually.

For example:

MENDER_MTDIDS = "nand0=20000000.flash"
MENDER_IS_ON_MTDID = "20000000.flash"

See also MENDER_MTDIDS.

MENDER_KERNEL_IMAGETYPE_FORCE

Value: <kernel image type> (default: value of KERNEL_IMAGETYPE)

In certain build scenarios, the detection of kernel image type may not work for specific boards. This is usually caused by custom post-processing steps required to generate the images bypassing the standard Yocto logic. Setting this variable will ensure that Mender packages the proper files in these cases.

MENDER_MBR_BOOTLOADER_FILE

Value: <MBR bootloader filename> (default: platform dependent)

Specifies a first stage bootloader to flash to the very first sector of the storage device (Master Boot Record, or "MBR"), in the same sector as the partition table. This is often used on BIOS based systems and frequently in combination with MENDER_IMAGE_BOOTLOADER_FILE to flash a second stage bootloader on a later sector on the same storage device. The bootloader is normally very short, usually shorter than the sector size itself, so that the partition table will also fit on the same sector. The size of the bootloader is specified with MENDER_MBR_BOOTLOADER_LENGTH.

The default depends on which features are enabled. If mender-bios and mender-grub are enabled, then the default is the GRUB first stage bootloader, otherwise the default is empty.

MENDER_MBR_BOOTLOADER_LENGTH

Value: 446 (default)

The number of bytes to flash into the Master Boot Record (MBR) using MENDER_MBR_BOOTLOADER_FILE.

MENDER_MTD_UBI_DEVICE_NAME

Value: ubi (default)

The MTD part name where UBI volumes are stored.

Defaults to ubi when mender-ubi feature is on and building a .ubimg, otherwise the default is empty.

MENDER_MTDIDS

Value: <mtdids string> (no default, required if using UBI)

This variable is only required with the mender-ubi feature enabled. It lists the MTDID assignments on the system, separated by comma. For example:

MENDER_MTDIDS = "nand0=20000000.flash,nand1=30000000.flash"

If it has more than one entry, then MENDER_IS_ON_MTDID must be set too.

MENDER_MTDPARTS

Value: <mtdparts string> (default calculated from several factors)

This variable is only relevant with the mender-ubi feature enabled. The variable holds the MTDPARTS string for the Flash based device. Setting this variable is usually done automatically cases where it is possible, but some cases requires setting it manually. For example:

MENDER_MTDPARTS = "20000000.flash:1m(u-boot),-(ubi)"

Two volume names have special meaning to the Mender mtdimg image builder:

• u-boot - The image builder will place the bootloader specified in MENDER_IMAGE_BOOTLOADER_FILE into this volume, if it is specified. Can be omitted if the platform doesn't need it.
• ubi - The ubimg image (UBI image) will be put into this volume. The ubi volume should virtually always be present.

See also MENDER_MTDIDS.

MENDER_NAND_FLASH_PAGE_SIZE

Value: 2048 (default)

This variable sets the page size, in bytes, of the NAND flash on the device, and is used to calculate parameters for the UBI volumes.

MENDER_PARTITIONING_OVERHEAD_KB

Value: <number> (default calculated from several factors)

A rough estimate of space lost due to partition alignment, expressed in KiB. The build process will calculate that automatically using a simple heuristic. See the definition of MENDER_PARTITIONING_OVERHEAD_KB in meta-mender for details on the calculation.

MENDER_PARTITION_ALIGNMENT

Value: <number> (default: value of MENDER_STORAGE_PEB_SIZE)

Alignment of partitions used when building partitioned images, expressed in bytes. Note that this is not always a whole number of KiB, particularly when the storage device is a UBI volume.

MENDER_ROOTFS_PART_A

Value: <block device> (default: 2nd partition on MENDER_STORAGE_DEVICE)

The partition Mender uses as the first (A) rootfs partition. See More detailed storage configuration for more information.

MENDER_ROOTFS_PART_A_NAME

Value: <name> (default: platform dependent)

Alternative name for MENDER_ROOTFS_PART_A. Used if you need two different references to MENDER_ROOTFS_PART_A.

Example:

# will only accept a UBI volume name (but we normally work with index numbers e.g. `mender_boot_part`)
ubifsmount ubi0:rootfsa

Defaults to the value of ${MENDER_ROOTFS_PART_A} when building .biosimg, .sdimg or .uefiimg.

Defaults to ${MENDER_STORAGE_DEVICE}:rootfsa when building .ubimg.

MENDER_ROOTFS_PART_B

Value: <block device> (default: 3rd partition on MENDER_STORAGE_DEVICE)

The partition Mender uses as the second (B) rootfs partition. See More detailed storage configuration for more information.

MENDER_ROOTFS_PART_B_NAME

Value: <name> (default: platform dependent)

See MENDER_ROOTFS_PART_A_NAME

Defaults to the value of ${MENDER_ROOTFS_PART_B} when building .biosimg, .sdimg or .uefiimg.

Defaults to ${MENDER_STORAGE_DEVICE}:rootfsb when building .ubimg.

MENDER_SERVER_URL

Value: https://docker.mender.io (default)

Variable to override the URL of the server for the client to connect to. It is also used for add-ons configuration, where enabled.

MENDER_CONNECT_USER

Value: nobody (default)

Variable holding the username which the mender-connect employs. See Mender shell configuration options. Note that the default value in meta-mender-core is nobody, while in meta-mender-demo it is root.

MENDER_STATE_SCRIPTS

Value: ${S}/mender-state-scripts ${MENDER_STATE_SCRIPTS_DIR} (default)

Variable to override the location of state scripts. See MENDER_STATE_SCRIPTS_DIR for more information.

MENDER_STATE_SCRIPTS_DIR

Value: ${B}/mender-state-scripts (default)

Only usable inside recipes that inherit mender-state-scripts. Recipes can put executable binaries or scripts into this location to have the scripts be included as state scripts for the Mender artifact. This should be done inside the do_compile task of a recipe.

If neither building nor other preprocessing is necessary then it is also possible to list a source archive in SRC_URI that extracts directly into ${PN}-${PV}/mender-state-scripts, where $PN and ${PV} are the usual Bitbake values of recipe name and version, respectively.

And finally, it is possible to set MENDER_STATE_SCRIPTS (note the missing _DIR) manually to a location containing state scripts, however it is recommended to use one of the two above methods.

You cannot mix the three methods.

MENDER_STORAGE_DEVICE

Value: /dev/mmcblk0 (default)

The storage device holding all partitions (rootfs, boot, data) used by Mender. See Configuring storage for more information.

MENDER_STORAGE_PEB_SIZE

Value: 8388608 (default)

Holds the size, in bytes, of the physical erase blocks (PEBs) on the Flash device.

MENDER_STORAGE_TOTAL_SIZE_MB

Value: 1024 (default)

Total size of the physical storage medium that mender partitioned images will be written to, expressed in MiB. The size of rootfs partition will be calculated automatically by subtracting the sizes of boot (see MENDER_BOOT_PART_SIZE_MB) and data partitions (see MENDER_DATA_PART_SIZE_MB) along with some predefined overhead (see MENDER_PARTITIONING_OVERHEAD_KB)). Default value is 1024.

MENDER_SWAP_PART_SIZE_MB

Value: 0 (default)

The size of the optional swap partition in the generated .biosimg, .sdimg or .uefiimg file. By default no swap partition is created, setting this variable to a value greater than zero will add one after the other partitions.

MENDER_TENANT_TOKEN

Value: <tenant token string> (default: empty)

Set this variable in local.conf in order to make the device recognize the organization account to which it belongs. This option should always be set, except when running a custom Mender Server installation with multitenancy module disabled.

MENDER_UBI_LEB_PEB_BLOCK_OVERHEAD

Value: <number> (default: 128 for NOR Flash, ${MENDER_NAND_FLASH_PAGE_SIZE} * 2 for NAND Flash)

The overhead that each logical erase block (LEB) of the UBI device adds to the physical erase block (PEB), in bytes. In other words, how many bytes are "wasted" in each LEB. Usually set automatically, but can be overridden.

MENDER_UBI_LEB_SIZE

Value: <number> (default: ${MENDER_STORAGE_PEB_SIZE} - ${MENDER_UBI_LEB_PEB_BLOCK_OVERHEAD})

The size of each logical erase block (LEB) on the UBI device, in bytes. Usually set automatically from the various MENDER_UBI_*_OVERHEAD variables, but can be overridden.

MENDER_UBI_TOTAL_BAD_PEB_OVERHEAD

Value: <number> (default: 0 for NOR Flash, 20 per PEB block for NAND Flash)

Total overhead on the whole UBI device, in bytes, reserved for bad physical erase blocks (PEBs). Usually zero for NOR Flash or a variable amount for NAND Flash.

MENDER_UBOOT_ENV_STORAGE_DEVICE_OFFSET

Value: <number> (default: Value of MENDER_PARTITION_ALIGNMENT)

Specifies the offset from the start of the raw block storage for placing the U-Boot environment, expressed in bytes. The default is equal to MENDER_PARTITION_ALIGNMENT_KB (converted to bytes), and must align with MENDER_PARTITION_ALIGNMENT_KB if the value is overwritten.

MENDER_UBOOT_POST_SETUP_COMMANDS

Value: <U-Boot command string> (default: empty)

A set of U-Boot commands to executed at the end of the MENDER_SETUP code in the MENDER_BOOTENV.

MENDER_UBOOT_PRE_SETUP_COMMANDS

Value: <U-Boot command string> (default: empty)

A set of U-Boot commands to executed at the beginning of the MENDER_SETUP code in the MENDER_BOOTENV.

MENDER_UBOOT_STORAGE_DEVICE

Value: <U-Boot storage device> (default: empty)

The storage device, as referred to by U-Boot (e.g. 1). This variable can be used in cases where the Linux kernel and U-Boot refer to the same device with different names. See The bootloader and the Linux kernel do not agree about the indexes of storage devices for more information.

If the variable is empty, it is automatically deduced from MENDER_STORAGE_DEVICE.

MENDER_UBOOT_STORAGE_INTERFACE

Value: <U-Boot storage interface> (default: empty)

The storage interface, as referred to by U-Boot (e.g. mmc). This variable can be used in cases where the Linux kernel and U-Boot refer to the same device with different names. See The bootloader and the Linux kernel do not agree about the indexes of storage devices for more information.

If the variable is empty, it is automatically deduced from MENDER_STORAGE_DEVICE.

SYSTEMD_AUTO_ENABLE:pn-mender

Value: enable (default)

Controls whether to run Mender as a systemd service. See Modes of operations and Image configuration for more information.