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

Grahame Bowland grahame at angrygoats.net
Tue Dec 23 00:08:39 WST 2008


2008/12/23 Robert P. J. Day <rpjday at crashcourse.ca>:
> On Mon, 22 Dec 2008, Robert P. J. Day wrote:
>
>>
>>   i suspect i already know the answer to this, but is there any way to
>> run dropbear on a system whose /dev directory is part of a larger
>> romfs?
>>
>>   ssh to such a system worked fine during development when the root
>> filesystem was NFS mounted and, therefore, writable.  but once that
>> rootfs is flashed and is now mounted as a romfs, not surprisingly,
>> dropbear can no longer accept incoming requests because (i'm
>> guessing) while the appropriate /dev/ttyp[0-9] device files are there,
>> dropbear has no ability to change their owner/perms, is that it?
>> which generates the log error message:
>>
>>    pty_allocate: openpty: No child processes
>>    no pty was allocated, couldn't execute
>>
>>   is there a way around this?  i would have guessed not, but i'm
>> willing to be pleasantly surprised.
>
>  actually, a thought just occurred to me.  i checked and, with an NFS
> mount with a writable /dev, an ssh session comes in and is associated
> with a /dev/ttyp[0-9] device file (the first available one).
>
>  is another option to mount the /dev/pts filesystem and, if so, would
> dropbear try to grab one of *those* device files instead?  since
> that's a pseudo filesystem, its device files should be writable, no?
> even when /dev itself isn't.

Hi Robert

Couldn't you mount a ramfs over /dev and create the necessary device files
in it? Should be easy enough to copy /dev to the ramfs first using tar or cpio.

Cheers
Grahame



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