openssh unix dev - Sep 2015 - Differentiating between ssh connection failures and ssh command failures

On Sat, Sep 12, 2015 at 11:14:07AM +1000, Damien Miller
wrote:
> ssh server.example.com /usr/bin/do/something
> r=$?
> if [ $r -eq 0 ] ; then
> 	echo success
> elif [ $r -eq 255 ] ; then
> 	echo ssh failed
> else
> 	echo command failed
> fi

ssh remoteserver exit 255

Hmm :-)

exit(-1)  aka exit(255) is a pretty standard "generic failure code"
for many programs.

The problem, really, is that "exit code" is the wrong thing to test
for.

x=`ssh remoteserver "echo CONNECTED && somecommand"`

And then see if CONNECTED appears in the output to show successful
connection.

-- 

rgds
Stephen

On 12 Sep 2015, at 03:13, Stephen Harris <lists at spuddy.org> wrote:
> On Sat, Sep 12, 2015 at 11:14:07AM +1000, Damien Miller wrote:
>> ssh server.example.com /usr/bin/do/something
>> r=$?
>> if [ $r -eq 0 ] ; then
>> 	echo success
>> elif [ $r -eq 255 ] ; then
>> 	echo ssh failed
>> else
>> 	echo command failed
>> fi
> 
> 
> ssh remoteserver exit 255
> 
> Hmm :-)
> 
> exit(-1)  aka exit(255) is a pretty standard "generic failure
code"
> for many programs.
That's *exactly* the issue I'm concerned about. Furthermore the server
is
not UNIX so I have no idea how to wrap it in something that makes it
return a different exit code.
> The problem, really, is that "exit code" is the wrong thing to
test for.
Well, I suppose there could be a CLI option to squash any non-zero
return codes from the remote into a single specified return code.
I don't think there is currently.
> x=`ssh remoteserver "echo CONNECTED && somecommand"`
> 
> And then see if CONNECTED appears in the output to show successful
> connection.
That's about as far as I got too. Technically that would fail to
differentiate between the shell being /bin/false and failure to
connect, but would be good enough for my use.

-- 
Alex Bligh

On Sep 12, 2015 7:30 PM, "Alex Bligh" <alex at alex.org.uk>
wrote:
> That's *exactly* the issue I'm concerned about. Furthermore the
server is
> not UNIX so I have no idea how to wrap it in something that makes it
> return a different exit code.
Use the control master / mux function in the ssh client?  That way the
connection establishment and command requests will be separate invocations
and you can check their return codes independently.

true. but never found this to be a problem in practice?
> Am 12.09.2015 um 04:13 schrieb Stephen Harris <lists at spuddy.org>:
> 
> On Sat, Sep 12, 2015 at 11:14:07AM +1000, Damien Miller wrote:
>> ssh server.example.com /usr/bin/do/something
>> r=$?
>> if [ $r -eq 0 ] ; then
>> 	echo success
>> elif [ $r -eq 255 ] ; then
>> 	echo ssh failed
>> else
>> 	echo command failed
>> fi
> 
> 
> ssh remoteserver exit 255
> 
> Hmm :-)
> 
> exit(-1)  aka exit(255) is a pretty standard "generic failure
code"
> for many programs.
> 
> The problem, really, is that "exit code" is the wrong thing to
test for.
> 
> x=`ssh remoteserver "echo CONNECTED && somecommand"`
> 
> And then see if CONNECTED appears in the output to show successful
> connection.
> 
> -- 
> 
> rgds
> Stephen
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