Identity

We recommend that you first read the overview on Identity in order to familiarize yourself with the concept and how it is used in Mender. This tutorial is about how to change the identity scheme and attributes reported by the Mender client.

Example device identities

Even though Mender allows several attributes to make up the device identity, most environments just use one attribute for simplicity.

For example, a MAC address of the primary interface satisfies the requirements for device identity:

ID={
MAC=56:84:7a:fe:97:99
}

Another example would be an eMMC CID:

ID={
# cat /sys/class/mmc_host/mmc0/mmc0\:0001/cid 
CID=90014a484247346132a4528894a9a300
}

You can also use the serial number of a device:

ID={
SerialNumber=PF021XD5
}

In some cases, several attributes form a device identity:

ID={
Generation=2
Model=3
DeviceNumber=1800
}

The Mender client works with all of these schemes, but note that you should only use one of them. For example, it does not make much sense to use the serial number to identify some devices, but the MAC address to identify others.

Implement a device identity executable

The Mender client obtains the identity attributes by running an executable (e.g. binary or script) named mender-device-identity and parsing its standard output as the identity. The executable lives under /usr/share/mender/identity/mender-device-identity.

The executable must produce a set of attributes on standard output in the following key/value format:

key=value\n

For example:

mac=0a:1b:3d:fe:02:33
cpuid=1234123-ABC

You cannot use Newline characters as they will be stripped. If you want to include them in your key or value, encode them in a URL format (e.g. foo\nbar becomes foo%0Abar).

If an attribute appears multiple times, the client will translate it to a list. For example, this output:

mac=0a:1b:3d:fe:02:33
mac=0a:1b:3d:fe:02:34
cpuid=1234123-ABC

will result in the following attributes:

mac=[0a:1b:3d:fe:02:33, 0a:1b:3d:fe:02:34]
cpuid=1234123-ABC

Example device identity executables

Example scripts are provided in the support directory in the Mender client source code repository.