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Kyle
Asked: 2021-10-18 08:38:19 +0800 CST

How do I get logs from my dropbear-initramfs SSH host?

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I use dropbear-initramfs (like this) to decrypt the root drive on my Ubuntu 20.04.3 headless server. Recently the server was abruptly powered off (power went out I think?) and now the dropbear SSH server rejects my public key.

I can successfully connect a keyboard and monitor and type in my decryption key, and I can reach the full SSH server after that, but then I still have the same issue with the public key. I've checked /etc/dropbear-initramfs/{authorized_keys,config}, but everything seems as it should be.

I'd like to see what's happening from the dropbear SSH side, but I don't know how to view the logs. Any ideas?

UPDATE:

I've run sudo lsinitramfs /boot/initrd.img-5.4.0-90-generic which gives me something interesting:

...
etc/dropbear  # no etc/dropbear/authorized_keys!
etc/dropbear/config
etc/dropbear/dropbear_dss_host_key
etc/dropbear/dropbear_ecdsa_host_key
etc/dropbear/dropbear_rsa_host_key
...
root-IEiu10  # what is this folder and why is authorized_keys here?
root-IEiu10/.ssh
root-IEiu10/.ssh/authorized_keys

UPDATE2: I think my issue is related to this.

luks dropbear

1 Answers

  1. Best Answer

    After running through several rabbit holes, I finally found this post describing how newer SSH clients are starting to disable ssh-rsa authentication. Turns out that the solution was to temporarily add PubkeyAcceptedKeyTypes +ssh-rsa to my SSH config for this server. The long-term solution is to update dropbear, but this works for now.

    The strange root-XXXXX folder is as it should be apparently.

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