Capturing backgrounded dbclient command output

Steve Hein ssh at sgi.com
Sat Jul 31 22:01:47 WST 2010


I've continued to investigate this issue, and the problem
is specific to not having stdin available.   I found that
I don't see my output when I run this:

/tmp/dropbear-0.52/dbclient -y -i /tmp/id_rsa_db localhost pwd </dev/null

or when I do this:

/tmp/dropbear-0.52/dbclient -f -y -i /tmp/id_rsa_db localhost pwd


But openssh handles lack of stdin just fine, i.e.:

ssh localhost pwd < /dev/null

will still return the command output.



Is this dropbear behavior intentional?    If so, does anyone know
what I would need to change to fix it?

Thanks!
Steve






On 07/30/2010 02:10 PM, Steven Hein wrote:
> I've been using dropbear-0.52 happily for a long time now, but
> today I tried to write a shell script to execute multiple
> dbclient commands in parallel (backgrounded), capture
> their output, and then display it when all dbclient
> commands have finished.    But I can't seem to capture
> any output from the dbclient command.
>
> The target platform for this is an embedded platform
> running busybox....but I boiled it down to a simple
> failing case on my Fedora 12 box    (I built a brand
> new dbclient from the 0.52 tarball).
>
>
> Here's the simple failing case:
>
>
> #! /bin/sh
>
> (/tmp/dropbear-0.52/dbclient -y -i /tmp/id_rsa_db localhost pwd) >
> /tmp/tout &
> wait
>
>
> When this script completes, there is nothing in /tmp/tout
>
>
>
> When I run this script (same case, just using the openssh client
> instead):
>
> #! /bin/sh
>
> (ssh localhost pwd) > /tmp/tout &
> wait
>
>
> Then I have data in /tmp/out   (the output from the 'pwd' command).
>
>
>
>
> This problem only appears to happen when the dbclient command is run
> in the background from within a script.   If I run this command
> directly from the shell command prompt:
>
> (/tmp/dropbear-0.52/dbclient -y -i /tmp/id_rsa_db localhost pwd) >
> /tmp/tout &; wait
>
> Then /tmp/tout contains the output of the 'pwd' command.
>
>
>
> Has anyone else wrestled with this problem?    Any solutions or pointers?
>
>
> Thanks!
> Steve
>
>



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