how to run dropbear on a system with a R/O /dev?

[Matt Johnston]

On Mon, Dec 22, 2008 at 10:51:26AM -0500, Robert P. J. Day wrote:
> > We do have /dev/pts mounted, that may or may not make a difference
> > (didn't check the code).
> 
>   i may do that at the earliest possible opportunity, but here's
> what's happening.  certainly, without mounting /dev/pts, i expect a
> login failure since all of /dev is read-only.
> 
>   however, after i mount /dev/pts RW, i can see that i have two char
> device files under there:  /dev/pts[01].  and i've verified i can
> change their permissions with "chmod".  so that's a good sign -- that
> the contents under /dev/pts are modifiable, at least to that extent.
> 
>   however, when i try to ssh into that system from elsewhere and i
> watch the destination system /var/log/messages, i can see that the
> password authentication succeeds, after which i get an authpriv.warn
> log message complaining about syslogin_perform_logout: logout(pts/2)
> returned an error: No such file or directory

Devices in /dev/pts get "automatically" created by the
openpty() call made by Dropbear - you don't create files
there yourself.  The usual tool I use for debugging things
like this is strace - run "strace -f" on the main Dropbear
process, if it's available. Are there any other log messages
suggesting why it's failing? 

The "logout" log warning isn't something to worry about -
that just means that it couldn't write user login/logout
details to /var/log/wtmp or /var/log/utmp.  You can
configure Dropbear with --disable-loginfunc to avoid it
trying that.

Also to eliminate other factors, check that "ssh -T" to the
host works. That will skip the tty allocation stage
entirely, you should still be able to run commands like "ls"
and get output.

Cheers,
Matt