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Re^7: SSH2 - Asynchronous Opens & Synchronous Commands

by salva (Abbot)
on Apr 06, 2014 at 06:43 UTC ( #1081290=note: print w/replies, xml ) Need Help??

in reply to Re^6: SSH2 - Asynchronous Opens & Synchronous Commands
in thread SSH2 - Asynchronous Opens & Synchronous Commands

The connection and authentication phases are carried out by the OpenSSH client and it doesn't pass the cause of the failure back to the module.

An easy to implement workaround is to redirect the output of the master ssh process to a file and then, to retrieve it when something goes wrong.

my $ssh = Net::OpenSSH->new($host, master_stderr_file => "/tmp/ssh-std +err-$host", master_opts => ['-v'], ...);

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Re^8: SSH2 - Asynchronous Opens & Synchronous Commands
by 5haun (Scribe) on Apr 06, 2014 at 15:57 UTC

    Of course! (head slap) :)

    I was already gathering the info, but didn't think of using it to automatically pull the error:

    my $ssh_debug = 0; # verbose logging: 0-3 ... my $session_log_name = "ssh_$host.log"; open( my $session_log_fh, ">", $session_log_name ) or die "Failed to create logfile $session_log_name: $!"; binmode( $session_log_fh, ":unix" ); # unbuffer log file ... $ssh_session{$host} = Net::OpenSSH->new( # host $host, # automatically add new host keys to the user known hosts file +s # enable verbosity, if enabled master_opts => ($ssh_debug) ? [ -o => "StrictHostKeyChecking=no", "-" . "v" x $ssh_debug ] : [ -o => "StrictHostKeyChecking=no" ], # authentication user => $username, password => $password, # logging master_stderr_fh => $session_log_fh, # connection parameters timeout => $loginTO, port => $ssh_port, async => 1 ); }

    The '-v' to enable debugging is not required in this case, as the error message (or nothing) will be written to the file with $ssh_debug = 0. I believe the important concept here is the cause of error message always appears to be the last line output to the master_stderr_fh file. Something like the following (combined with the above) appears to provide a more accurate error message:

    elsif ( $ssh->error ) { # handle connection error my $lasterr = File::ReadBackwards->new("ssh_$host.log")->r +eadline; # ... something that outputs or logs the error message }

    It should be noted there will be a linefeed on the end of $lasterr (it's left up to the user to chomp it off if they don't want it).

    It should also be noted that master_stderr_fh cannot be assigned to an in-memory file, or the following error will be received:

    Not a GLOB reference at /usr/local/share/perl/5.14.2/Net/ li +ne 614. 612 sub _check_is_system_fh { 613 my ($name, $fh) = @_; 614 my $fn = fileno(defined $fh ? $fh : $name); 615 defined $fn and $fn >= 0 and return; 616 croak "child process $name is not a real system file handle"; 617 }

    Thanks again. The full solution will be posted when it is done (I'm juggling a couple of other things while doing this, so sorry it's taking a while).

      master_stderr_fh cannot be assigned to an in-memory file

      Yes, using scalars as files only works at the Perl level. They are not backed by operating system file handlers and so they are unsuitable for IPC.

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