Ssh – How to configure SSHD on CoreOS after installation

configurationcoreossshsystemd

I've got the CoreOS running and I would like to remove the ability to login using passwords to the sshd.
I went through the docs of the CoreOS in here, but I am quite new to the systemd. I went through the man page, but I am a bit lost on it.
I know I have to create a dropin file inside /etc/system.d/system/, but I have no idea, in which section of the file, should I put the PasswordAuthentication no option. Since I work remotely, I don't want to screw up and not be able to login again…

I would be grateful for some guidance.

Best Answer

After having a chat on #coreos on freenode, I have learned the simples thing of all.

/etc is not read only, but sshd_config is a symlink to a file on /usr which is. I just had to remove the symlink and create the file by hand... eh.

Related Solutions

SSH – How to Check SSHD Log

If no one else is using the system at the moment you could do what i've done in such cases:

stop sshd service (at least i've been able to do this while logged in via ssh)
start sshd manually and add some -d options to get more verbose debug output. Unless you have something funky going on it should use the same keys and config it does when started properly

How to set sysctl variables at CoreOS cloud-init

See answer on CoreOS github issue tracker: https://github.com/coreos/bugs/issues/747#issuecomment-142764415

There might be a simpler way in future, but for now you can simply write a unit to invoke systemd-sysctl during cloudinit; it'll be started after any files specified in write_files are written:
#cloud-config 
.... 
coreos:
  units:
    - name: update-sysctl.service
      command: start
      content: |
        [Unit]
        Description=Update sysctl values written by cloud-config
        [Service]
        ExecStart=/usr/lib/systemd/systemd-sysctl ...

Best Answer

Related Solutions

SSH – How to Check SSHD Log

How to set sysctl variables at CoreOS cloud-init

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