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

I'm sure this should be an easy question, but from the ssh client manpage:

EXIT STATUS
     ssh exits with the exit status of the remote command or with 255 if an
error occurred.


Let's say I'm using
    ssh server.example.com /usr/bin/do/something
in (e.g.) a bash script.

How can one differentiate between a failure of ssh to connect to the host and
the
command in question returning an error? I need to detect both, and differentiate
between them.

-- 
Alex Bligh

On Fri, 11 Sep 2015, Alex Bligh wrote:
> I'm sure this should be an easy question, but from the ssh client
manpage:
> 
> EXIT STATUS
>      ssh exits with the exit status of the remote command or with 255 if an
error occurred.
> 
> 
> Let's say I'm using
>     ssh server.example.com /usr/bin/do/something
> in (e.g.) a bash script.
> 
> How can one differentiate between a failure of ssh to connect to the host
and the
> command in question returning an error? I need to detect both, and
differentiate
> between them.
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

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