Confusion on SSH and PAM

[Vinny]

Replying to myself to fix my error.

Vinny wrote:
> Rakhesh Sasidharan wrote:
>>
> [snip]
>>
>> Here's another oddity I encountered today.
>>
>> If "PermitRootLogin" is set to "forced-commands-only", my 
>> understanding is the SSHD will permit root logins if a command to be 
>> executed is given. But that doesn't seem to be the case in practice! I 
>> have keys setup for root to login, but instead of letting me in with 
>> those keys, SSHD ignores them, passes me to PAM for password prompting 
>> (three times) and the denies me out! Very strange.
> 
> PermitRootLogin forced-commands-only
> 
> This requires that a command be present in the authorized_keys
> file for a given key.  For example, root's authorized_keys
> file might look like this for an rsync command:
> 
> command="/root/.ssh/cron/validate-rsync",from="10.10.10.2",no-port-forwarding,no-X11-forwarding,no-agent-forwarding 
> 
> ssh-dss AAAAB3N_more_public_key_data comment
> 
> The entire text above should be only one line in the file.
> The command shown in:
> 
>  command="/root/.ssh/cron/validate-rsync"
> 
> I.e. /root/.ssh/cron/validate-rsync
> 

This:

> must be the command submitted on the ssh command line, loosely:
> 
> $ ssh -i private_key_matching_public_key_in_authorized_keys root at host \
>  /root/.ssh/cron/validate-rsync
> 

is incorrect.  The command shown is the command that is executed
when the root user is authenticated via the key in question.  It
does not need to appear on any ssh command line.

> The root user cannot otherwise login to the system using ssh
> unless further keys with corresponding commands exist.
> 

Sorry about the error.

Vinny