Can't SSH using Net::OpenSSH, can through command line

Question

This is my first time working with Net::OpenSSH, and I am attempting to create an SSH for loop, where I print the hostname of the server I am on using whoami. I am ale to SSH to my intended servers from the command line, but when I run my script, I encounter the following error...

ssh: could not resolve hostname
: Name or service not known
username

To get more information, I printed the the output of $ssh->error, where $ssh is my Net::OpenSSH object.

unable to establish master SSH connection: bad password or master process exited unexpectedly at line 24, $fh line 1

This is the script so far...

#!/usr/bin/perl

 use strict;
 use warnings;
 use Net::OpenSSH;
 my $file = 'servers.txt';
 open (my $fh, $file) or die "Could not open";

 while (my $row = <$fh>) {
   my $user = "username";
   my $password = "password";
   my $ssh = Net::OpenSSH->new(host => $row, user => $user, password => $password);
   $ssh-error and die "SSH connection failed: " . $ssh->error;
   my $whoami = `whoami`;
   print $whoami;
 }

The servers.txt file is a plain text file with a list of the servers hostnames, one after another.

My understanding is that if I can SSH to these servers from the command line, the problem must lie in the script, and not the servers/network. Any insight into why I Net::OpenSSH cannot resolve a seemingly accessible server would be appreciated.

"Name or service not know" and "bad password or moster process exited" ... sigh — Sinan Ünür
– Sinan Ünür, Commented Jul 6, 2017 at 22:05
Welcome to SO. Please take the tour, read How to Ask, and most importantly in this specific case edit your question to include a Minimal, Complete, and Verifiable example. Any of this comment's helpfulness goes to @OldProgrammer, not me. — Jeff Holt
– Jeff Holt, Commented Jul 7, 2017 at 2:24
@jeff6times7 Apologies, and thank you for the message. I have edited the post to improve the quality. — cm_1nges
– cm_1nges, Commented Jul 7, 2017 at 4:13

Jeff Holt · Accepted Answer · 2017-07-07 04:43:49Z

2

"the problem must lie in the script" Yes, there are two problems with the script that I executed. The first one is a syntax error. Other commenters have noted it.

The line

   $ssh-error and die "SSH connection failed: " . $ssh->error;

should be

   $ssh->error and die "SSH connection failed: " . $ssh->error;

The other problem, which is coming from a version of the script that you haven't shown yet, and which was also noted by others, is that you didn't remove the trailing newline from $row. You do that with

chomp($row)

Do that as the opening instruction of the while block and you should be good to go.

I have to stress the importance of being extra careful in posting MCVs. Before you press that submit button, copy the code in your post to a temp file and execute it, and you will get fewer complaints from responders.

By the way, a good debugging habit that might have let you solve the problem on your own is to have added this line before executing Net::OpenSSH->new

print STDERR ";$row;\n" if $debugging;  # or something to this effect

If you had done this, you would have seen something like this on STDERR

;myhost
;

Additionally, the module you're using has a decent debugging feature mentioned in its pod. The debugging output is not so easy to interpret but if you have no idea where the problem is, then you might start there. If you had added this line

$Net::OpenSSH::debug = 8;

Then you would have seen this on STDERR

$ cat servers.txt
localhostx
$ perl x.pl
...
ssh: Could not resolve hostname localhostx
: nodename nor servname provided, or not known

which would have looked like this if you had called chomp but the hostname truly did not exist

ssh: Could not resolve hostname localhostx: nodename nor servname provided, or not known

edited Jul 7, 2017 at 4:43

answered Jul 7, 2017 at 4:27

Jeff Holt

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1 Comment

cm_1nges Over a year ago

Thanks @jeff6times7, using chomp worked. I tested your debugging advice as well, and was able to get a better idea of what my problem was. I appreciate the input on posting, I realize I should have been more careful before submitting my problem. Lesson learned.

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