Howto Update Coreos with Update Engine

Get engine options:
update_engine_client -help

Get update status
update_engine_client -status

Force Coreos an immediate update check:
update_engine_client -update

If the update fails you can check the logs of the update engine by running:
journalctl -u update-engine -o cat

If you want to download another update you may need to clear the reboot pending status:

update_engine_client -reset_status

Getting SSH_AUTH_SOCK environment variable Error for Fleetctl journal command at CoreOS

One way is it to put private key to ssh-agent

Append commands below to .bash_profile

eval  `ssh-agent -s`
ssh-add ~/.ssh/id_rsa


Then fleetctl journal command will run as expected.

Overrride cloud-config parameters installed by coreos-install

If you invested a lot of time to override config param that comes through installation, then carry on reading.

The installation script will process your cloud-config.yaml file specified with the -c flag and place it onto disk. It will be installed to /var/lib/coreos-install/user_data and evaluated on every boot.

For instance,  there is a simple config for coreos-install

#cloud-config

coreos:

  etcd:

    name: node001

    addr: 192.168.100.1:4001

    peer-addr: 192.168.100.1:7001

    discovery: <discoveriy ip>

  units:

    - name: etcd.service

      command: start

There are two way to override config parameter:

1. Override systemd service by etcd.service.d/override.conf:
2. Override coreos installation script under /var/lib/coreos-install/user_data

I prefer to edit /var/lib/coreos-install/user_data and run coreos-cloudinit to update configurations.