When we create a MC that declares the same kernel argument twice, MCO is adding it only once.

$ oc get clusterversion
NAME      VERSION                              AVAILABLE   PROGRESSING   SINCE   STATUS
version   4.12.0-0.nightly-2023-09-22-181920   True        False         5h18m   Cluster version is 4.12.0-0.nightly-2023-09-22-181920

We have seen this behavior in 4.15 too 4.15.0-0.nightly-2023-09-22-224720

Always

1. Create a MC that declares 2 kernel arguments with the same value (z=4 is duplicated)

 apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  labels:
    machineconfiguration.openshift.io/role: worker
  name: test-kernel-arguments-32-zparam
spec:
  config:
    ignition:
      version: 3.2.0
  kernelArguments:
    - y=0
    - z=4
    - y=1
    - z=4

We get the following parameters

$ oc debug -q node/sergio-v12-9vwrc-worker-c-tpbvh.c.openshift-qe.internal  -- chroot /host cat /proc/cmdline
BOOT_IMAGE=(hd0,gpt3)/ostree/rhcos-a594b3a14778ce39f2b42ddb90e933c1971268a746ef1678a3c6eedee5a21b00/vmlinuz-4.18.0-372.73.1.el8_6.x86_64 ostree=/ostree/boot.0/rhcos/a594b3a14778ce39f2b42ddb90e933c1971268a746ef1678a3c6eedee5a21b00/0 ignition.platform.id=gcp console=ttyS0,115200n8 root=UUID=e101e976-e029-411d-ad71-6856f3838c4f rw rootflags=prjquota boot=UUID=75598fe5-c10d-4e95-9747-1708d9fe6a10 console=tty0 y=0 z=4 y=1

There is only one "z=4" parameter. We should see "y=0 z=4 y=1 z=4" instead of "y=0 z=4 y=1"

In older versions we can see that the duplicated parameters are created

For example, this is the output in a IPI on AWS 4.9 cluster

$ oc debug -q node/ip-10-0-189-69.us-east-2.compute.internal -- chroot /host cat /proc/cmdline
BOOT_IMAGE=(hd0,gpt3)/ostree/rhcos-e1eeff6ec1b9b70a3554779947906f4a7fb93e0d79fbefcb045da550b7d9227f/vmlinuz-4.18.0-305.97.1.el8_4.x86_64 random.trust_cpu=on console=tty0 console=ttyS0,115200n8 ostree=/ostree/boot.1/rhcos/e1eeff6ec1b9b70a3554779947906f4a7fb93e0d79fbefcb045da550b7d9227f/0 ignition.platform.id=aws root=UUID=ed307195-b5a9-4160-8a7a-df42aa734c28 rw rootflags=prjquota y=0 z=4 y=1 z=4


All the parameters are created, including the duplicated "z=4".