Excellent summary. In short, the bootstrap process is one time only.

On Jul 22, 2026, at 5:41 AM, Eugen Block via ceph-users <ceph-users@ceph.io> wrote:

Hi, responses inline...

Zitat von Michel Le Cocq via ceph-users <ceph-users@ceph.io>:

...

Actually, what confused me was this:

cephadm bootstrap --mon-ip <my-ip>

Among other things, this command: - Generates a new SSH key for the Ceph cluster and adds it to the /root/.ssh/authorized_keys file. - Saves a copy of the public key to the /etc/ceph/ceph.pub file.

You then need to add a node.

ssh-copy-id -f -i /etc/ceph/ceph.pub root@<new-host>

ceph orch host add <newhost> [<ip>] [<label1> ...]

I wondered where the private part of the SSH key /etc/ceph/ceph.pub was !

That's stored in the config-key db:

ceph config-key get mgr/cephadm/ssh_identity_key

...

-- M

Michel Le Cocq via ceph-users <ceph-users@ceph.io> writes:

...

Hi again.

I'm answering my own question.

It seems I read the wrong version of the doc ... sic!

It should be enough to set the “_admin” flag on all nodes:

and that we also need to install cephadm on the nodes we want to use for administration, right!?

Not necessarily, but it can be more convenient for debugging. The orchestrator stores a cephadm binary on each node to be able to manage them, it is stored in /var/lib/ceph/{FSID}/cephadm.{SOME_DIGEST}. That's used to remotely orchestrate the cluster/nodes etc. The original bootstrap node requires a cephadm binary either installed as a package or downloaded via curl as described in the docs to be able to bootstrap. After that you'll only need to execute cephadm commands locally on the nodes if you're debugging issues etc., otherwise the orchestrator will only use the file in /var/lib/ceph.

...

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