1Net::OpenSSH(3)       User Contributed Perl Documentation      Net::OpenSSH(3)
2
3
4

NAME

6       Net::OpenSSH - Perl SSH client package implemented on top of OpenSSH
7

SYNOPSIS

9         use Net::OpenSSH;
10
11         my $ssh = Net::OpenSSH->new($host);
12         $ssh->error and
13           die "Couldn't establish SSH connection: ". $ssh->error;
14
15         $ssh->system("ls /tmp") or
16           die "remote command failed: " . $ssh->error;
17
18         my @ls = $ssh->capture("ls");
19         $ssh->error and
20           die "remote ls command failed: " . $ssh->error;
21
22         my ($out, $err) = $ssh->capture2("find /root");
23         $ssh->error and
24           die "remote find command failed: " . $ssh->error;
25
26         my ($rin, $pid) = $ssh->pipe_in("cat >/tmp/foo") or
27           die "pipe_in method failed: " . $ssh->error;
28
29         print $rin "hello\n";
30         close $rin;
31
32         my ($rout, $pid) = $ssh->pipe_out("cat /tmp/foo") or
33           die "pipe_out method failed: " . $ssh->error;
34
35         while (<$rout>) { print }
36         close $rout;
37
38         my ($in, $out ,$pid) = $ssh->open2("foo");
39         my ($pty, $pid) = $ssh->open2pty("foo");
40         my ($in, $out, $err, $pid) = $ssh->open3("foo");
41         my ($pty, $err, $pid) = $ssh->open3pty("login");
42
43         my $sftp = $ssh->sftp();
44         $sftp->error and die "SFTP failed: " . $sftp->error;
45

DESCRIPTION

47       Net::OpenSSH is a secure shell client package implemented on top of
48       OpenSSH binary client ("ssh").
49
50   Under the hood
51       This package is implemented around the multiplexing feature found in
52       later versions of OpenSSH. That feature allows one to run several
53       sessions over a single SSH connection (OpenSSH 4.1 was the first one to
54       provide all the required functionality).
55
56       When a new Net::OpenSSH object is created, the OpenSSH "ssh" client is
57       run in master mode, establishing a persistent (for the lifetime of the
58       object) connection to the server.
59
60       Then, every time a new operation is requested a new "ssh" process is
61       started in slave mode, effectively reusing the master SSH connection to
62       send the request to the remote side.
63
64   Net::OpenSSH Vs. Net::SSH::.* modules
65       Why should you use Net::OpenSSH instead of any of the other Perl SSH
66       clients available?
67
68       Well, this is my (biased) opinion:
69
70       Net::SSH::Perl is not well maintained nowadays (update: a new
71       maintainer has stepped in so this situation could change!!!), requires
72       a bunch of modules (some of them very difficult to install) to be
73       acceptably efficient and has an API that is limited in some ways.
74
75       Net::SSH2 is much better than Net::SSH::Perl, but not completely stable
76       yet. It can be very difficult to install on some specific operating
77       systems and its API is also limited, in the same way as Net::SSH::Perl.
78
79       Using Net::SSH::Expect, in general, is a bad idea. Handling interaction
80       with a shell via Expect in a generic way just can not be reliably done.
81
82       Net::SSH is just a wrapper around any SSH binary commands available on
83       the machine. It can be very slow as they establish a new SSH connection
84       for every operation performed.
85
86       In comparison, Net::OpenSSH is a pure perl module that does not have
87       any mandatory dependencies (obviously, besides requiring OpenSSH
88       binaries).
89
90       Net::OpenSSH has a very perlish interface. Most operations are
91       performed in a fashion very similar to that of the Perl builtins and
92       common modules (e.g. IPC::Open2).
93
94       It is also very fast. The overhead introduced by launching a new ssh
95       process for every operation is not appreciable (at least on my Linux
96       box). The bottleneck is the latency intrinsic to the protocol, so
97       Net::OpenSSH is probably as fast as an SSH client can be.
98
99       Being based on OpenSSH is also an advantage: a proved, stable, secure
100       (to paranoid levels), inseparably and well maintained implementation of
101       the SSH protocol is used.
102
103       On the other hand, Net::OpenSSH does not work on Windows, not even
104       under Cygwin.
105
106       Net::OpenSSH specifically requires the OpenSSH SSH client (AFAIK, the
107       multiplexing feature is not available from any other SSH client).
108       However, note that it will interact with any server software, not just
109       servers running OpenSSH "sshd".
110
111       For password authentication, IO::Pty has to be installed. Other modules
112       and binaries are also required to implement specific functionality (for
113       instance Net::SFTP::Foreign, Expect or rsync(1)).
114
115       Net::OpenSSH and Net::SSH2 do not support version 1 of the SSH
116       protocol.
117

API

119   Optional arguments
120       Almost all methods in this package accept as first argument an optional
121       reference to a hash containing parameters ("\%opts"). For instance,
122       these two method calls are equivalent:
123
124         my $out1 = $ssh->capture(@cmd);
125         my $out2 = $ssh->capture({}, @cmd);
126
127   Error handling
128       Most methods return undef (or an empty list) to indicate failure.
129
130       The "error" method can always be used to explicitly check for errors.
131       For instance:
132
133         my ($output, $errput) = $ssh->capture2({timeout => 1}, "find /");
134         $ssh->error and die "ssh failed: " . $ssh->error;
135
136   Net::OpenSSH methods
137       These are the methods provided by the package:
138
139       Net::OpenSSH->new($host, %opts)
140           Creates a new SSH master connection
141
142           $host can be a hostname or an IP address. It may also contain the
143           name of the user, her password and the TCP port number where the
144           server is listening:
145
146              my $ssh1 = Net::OpenSSH->new('jack@foo.bar.com');
147              my $ssh2 = Net::OpenSSH->new('jack:secret@foo.bar.com:10022');
148              my $ssh3 = Net::OpenSSH->new('jsmith@2001:db8::1428:57ab'); # IPv6
149
150           IPv6 addresses may optionally be enclosed in brackets:
151
152              my $ssh4 = Net::OpenSSH->new('jsmith@[::1]:1022');
153
154           This method always succeeds in returning a new object. Error
155           checking has to be performed explicitly afterwards:
156
157             my $ssh = Net::OpenSSH->new($host, %opts);
158             $ssh->error and die "Can't ssh to $host: " . $ssh->error;
159
160           If you have problems getting Net::OpenSSH to connect to the remote
161           host read the troubleshooting chapter near the end of this
162           document.
163
164           Accepted options:
165
166           user => $user_name
167               Login name
168
169           port => $port
170               TCP port number where the server is running
171
172           password => $password
173               User given password for authentication.
174
175               Note that using password authentication in automated scripts is
176               a very bad idea. When possible, you should use public key
177               authentication instead.
178
179           passphrase => $passphrase
180               Uses given passphrase to open private key.
181
182           key_path => $private_key_path
183               Uses the key stored on the given file path for authentication.
184
185           gateway => $gateway
186               If the given argument is a gateway object as returned by
187               "find_gateway" in Net::OpenSSH::Gateway method, use it to
188               connect to the remote host.
189
190               If it is a hash reference, call the "find_gateway" method
191               first.
192
193               For instance, the following code fragments are equivalent:
194
195                 my $gateway = Net::OpenSSH::Gateway->find_gateway(
196                         proxy => 'http://proxy.corporate.com');
197                 $ssh = Net::OpenSSH->new($host, gateway => $gateway);
198
199               and
200
201                 $ssh = Net::OpenSSH->new($host,
202                         gateway => { proxy => 'http://proxy.corporate.com'});
203
204           proxy_command => $proxy_command
205               Use the given command to establish the connection to the remote
206               host (see "ProxyCommand" on ssh_config(5)).
207
208           batch_mode => 1
209               Disables querying the user for password and passphrases.
210
211           ctl_dir => $path
212               Directory where the SSH master control socket will be created.
213
214               This directory and its parents must be writable only by the
215               current effective user or root, otherwise the connection will
216               be aborted to avoid insecure operation.
217
218               By default "~/.libnet-openssh-perl" is used.
219
220           ctl_path => $path
221               Path to the SSH master control socket.
222
223               Usually this option should be avoided as the module is able to
224               pick an unused socket path by itself. An exception to that rule
225               is when the "external_master" feature is enabled.
226
227               Note that the length of the path is usually limited to between
228               92 and 108 bytes, depending of the underlying operating system.
229
230           ssh_cmd => $cmd
231               Name or full path to OpenSSH "ssh" binary. For instance:
232
233                 my $ssh = Net::OpenSSH->new($host, ssh_cmd => '/opt/OpenSSH/bin/ssh');
234
235           scp_cmd => $cmd
236               Name or full path to OpenSSH "scp" binary.
237
238               By default it is inferred from the "ssh" one.
239
240           rsync_cmd => $cmd
241               Name or full path to "rsync" binary. Defaults to "rsync".
242
243           remote_shell => $name
244               Name of the remote shell. Used to select the argument quoter
245               backend.
246
247           timeout => $timeout
248               Maximum acceptable time that can elapse without network traffic
249               or any other event happening on methods that are not immediate
250               (for instance, when establishing the master SSH connection or
251               inside methods "capture", "system", "scp_get", etc.).
252
253               See also "Timeouts".
254
255           kill_ssh_on_timeout => 1
256               This option tells Net::OpenSSH to kill the local slave SSH
257               process when some operation times out.
258
259               See also "Timeouts".
260
261           strict_mode => 0
262               By default, the connection will be aborted if the path to the
263               socket used for multiplexing is found to be non-secure (for
264               instance, when any of the parent directories is writable by
265               other users).
266
267               This option can be used to disable that feature. Use with
268               care!!!
269
270           async => 1
271               By default, the constructor waits until the multiplexing socket
272               is available. That option can be used to defer the waiting
273               until the socket is actually used.
274
275               For instance, the following code connects to several remote
276               machines in parallel:
277
278                 my (%ssh, %ls);
279                 # multiple connections are established in parallel:
280                 for my $host (@hosts) {
281                     $ssh{$host} = Net::OpenSSH->new($host, async => 1);
282                 }
283                 # then to run some command in all the hosts (sequentially):
284                 for my $host (@hosts) {
285                     $ssh{$host}->system('ls /');
286                 }
287
288           connect => 0
289               Do not launch the master SSH process yet.
290
291           master_opts => [...]
292               Additional options to pass to the "ssh" command when
293               establishing the master connection. For instance:
294
295                 my $ssh = Net::OpenSSH->new($host,
296                     master_opts => [-o => "ProxyCommand corkscrew httpproxy 8080 $host"]);
297
298           default_ssh_opts => [...]
299               Default slave SSH command line options for "open_ex" and
300               derived methods.
301
302               For instance:
303
304                 my $ssh = Net::OpenSSH->new($host,
305                     default_ssh_opts => [-o => "ConnectionAttempts=0"]);
306
307           forward_agent => 1
308               Enables forwarding of the authentication agent.
309
310               This option can not be used when passing a passphrase (via
311               "passphrase") to unlock the login private key.
312
313               Note that Net::OpenSSH will not run "ssh-agent" for you. This
314               has to be done ahead of time and the environment variable
315               "SSH_AUTH_SOCK" set pointing to the proper place.
316
317           forward_X11 => 1
318               Enables forwarding of the X11 protocol
319
320           default_stdin_fh => $fh
321           default_stdout_fh => $fh
322           default_stderr_fh => $fh
323               Default I/O streams for "open_ex" and derived methods
324               (currently, that means any method but "pipe_in" and "pipe_out"
325               and I plan to remove those exceptions soon!).
326
327               For instance:
328
329                 open my $stderr_fh, '>>', '/tmp/$host.err' or die ...;
330                 open my $stdout_fh, '>>', '/tmp/$host.log' or die ...;
331
332                 my $ssh = Net::OpenSSH->new($host, default_stderr_fh => $stderr_fh,
333                                                    default_stdout_fh => $stdout_fh);
334                 $ssh->error and die "SSH connection failed: " . $ssh->error;
335
336                 $ssh->scp_put("/foo/bar*", "/tmp")
337                   or die "scp failed: " . $ssh->error;
338
339           default_stdin_file = $fn
340           default_stdout_file = $fn
341           default_stderr_file = $fn
342               Opens the given file names and use them as the defaults.
343
344           master_stdout_fh => $fh
345           master_stderr_fh => $fh
346               Redirect corresponding stdio streams of the master SSH process
347               to given filehandles.
348
349           master_stdout_discard => $bool
350           master_stderr_discard => $bool
351               Discard corresponding stdio streams.
352
353           expand_vars => $bool
354               Activates variable expansion inside command arguments and file
355               paths.
356
357               See "Variable expansion" below.
358
359           vars => \%vars
360               Initial set of variables.
361
362           external_master => 1
363               Instead of launching a new OpenSSH client in master mode, the
364               module tries to reuse an already existent one. "ctl_path" must
365               also be passed when this option is set. See also
366               "get_ctl_path".
367
368               Example:
369
370                 $ssh = Net::OpenSSH->new('foo', external_master => 1, ctl_path = $path);
371
372               When "external_master" is set, the hostname argument becomes
373               optional (0.0.0.0 is passed to OpenSSH which does not use it at
374               all).
375
376           default_encoding => $encoding
377           default_stream_encoding => $encoding
378           default_argument_encoding => $encoding
379               Set default encodings. See "Data encoding".
380
381           password_prompt => $string
382           password_prompt => $re
383               By default, when using password authentication, the module
384               expects the remote side to send a password prompt matching
385               "/[?:]/".
386
387               This option can be used to override that default for the rare
388               cases when a different prompt is used.
389
390               Examples:
391
392                  password_prompt => ']'; # no need to escape ']'
393                  password_prompt => qr/[:?>]/;
394
395           login_handler => \&custom_login_handler
396               Some remote SSH server may require a custom
397               login/authentication interaction not natively supported by
398               Net::OpenSSH. In that cases, you can use this option to replace
399               the default login logic.
400
401               The callback will be invoked repeatedly as
402               "custom_login_handler($ssh, $pty, $data)" where $ssh is the
403               current Net::OpenSSH object, "pty" a IO::Pty object attached to
404               the slave "ssh" process tty and $data a reference to an scalar
405               you can use at will.
406
407               The login handler must return 1 after the login process has
408               completed successfully or 0 in case it still needs to do
409               something else. If some error happens, it must die.
410
411               Note, that blocking operations should not be performed inside
412               the login handler (at least if you want the "async" and
413               "timeout" features to work).
414
415               See also the sample script "login_handler.pl" in the "examples"
416               directory.
417
418               Usage of this option is incompatible with the "password" and
419               "passphrase" options, you will have to handle password or
420               passphrases from the custom handler yourself.
421
422           master_setpgrp => 1
423               When this option is set, the master process is run as a
424               different process group. As a consequence it will not die when
425               the user presses Ctrl-C at the terminal.
426
427               In order to allow the master SSH process to request any
428               information from the user, the module may set it as the
429               terminal controlling process while the connection is
430               established (using "tcsetpgrp" in POSIX). Afterwards, the
431               terminal controlling process is reset.
432
433               This feature is highly experimental. Report any problems you
434               may find, please.
435
436           master_pty_force => 1
437               By default, Net::OpenSSH attaches the master SSH process to a
438               pty only when some kind of interactive authentication is
439               requested. If this flag is set a pty will be attached always.
440
441               That allows to get better diagnostics for some kind of errors
442               (as for instance, bad host keys) and also allows to retrieve
443               the pty log using get_master_pty_log.
444
445       $ssh->error
446           Returns the error condition for the last performed operation.
447
448           The returned value is a dualvar as $! (see "$!" in perlvar) that
449           renders an informative message when used in string context or an
450           error number in numeric context (error codes appear in
451           Net::OpenSSH::Constants).
452
453       $ssh->get_master_pty_log
454           In order to handle password authentication or entering the
455           passphrase for a private key, Net::OpenSSH may run the master SSH
456           process attached to a pty.
457
458           In that case and after a constructor call returns a connection
459           failure error, this method can be called to retrieve the output
460           captured at the pty (the log is discarded when the connection is
461           established successfully).
462
463           Any data consumed from the pty by custom login handlers will be
464           missing from the the returned log.
465
466       $ssh->get_user
467       $ssh->get_host
468       $ssh->get_port
469           Return the corresponding SSH login parameters.
470
471       $ssh->get_ctl_path
472           Returns the path to the socket where the OpenSSH master process
473           listens for new multiplexed connections.
474
475       ($in, $out, $err, $pid) = $ssh->open_ex(\%opts, @cmd)
476           Note: this is a low level method which, probably, you do not need
477           to use!
478
479           That method starts the command @cmd on the remote machine creating
480           new pipes for the IO channels as specified on the %opts hash.
481
482           If @cmd is omitted, the remote user shell is run.
483
484           Returns four values, the first three ($in, $out and $err)
485           correspond to the local side of the pipes created (they can be
486           undef) and the fourth ($pid) to the PID of the new SSH slave
487           process. An empty list is returned on failure.
488
489           Note that "waitpid" has to be used afterwards to reap the slave SSH
490           process.
491
492           Accepted options:
493
494           stdin_pipe => 1
495               Creates a new pipe and connects the reading side to the stdin
496               stream of the remote process. The writing side is returned as
497               the first value ($in).
498
499           stdin_pty => 1
500               Similar to "stdin_pipe", but instead of a regular pipe it uses
501               a pseudo-tty (pty).
502
503               Note that on some operating systems (e.g. HP-UX, AIX), ttys are
504               not reliable. They can overflow when large chunks are written
505               or when data is written faster than it is read.
506
507           stdin_fh => $fh
508               Duplicates $fh and uses it as the stdin stream of the remote
509               process.
510
511           stdin_file => $filename
512           stdin_file => \@open_args
513               Opens the file of the given name for reading and uses it as the
514               remote process stdin stream.
515
516               If an array reference is passed its contents are used as the
517               arguments for the underlying open call. For instance:
518
519                 $ssh->system({stdin_file => ['-|', 'gzip -c -d file.gz']}, $rcmd);
520
521           stdin_discard => 1
522               Uses /dev/null as the remote process stdin stream.
523
524           stdout_pipe => 1
525               Creates a new pipe and connects the writing side to the stdout
526               stream of the remote process. The reading side is returned as
527               the second value ($out).
528
529           stdout_pty => 1
530               Connects the stdout stream of the remote process to the pseudo-
531               pty. This option requires "stdin_pty" to be also set.
532
533           stdout_fh => $fh
534               Duplicates $fh and uses it as the stdout stream of the remote
535               process.
536
537           stdout_file => $filename
538           stdout_file => \@open_args
539               Opens the file of the given filename and redirect stdout there.
540
541           stdout_discard => 1
542               Uses /dev/null as the remote process stdout stream.
543
544           stdinout_socket => 1
545               Creates a new socketpair, attaches the stdin an stdout streams
546               of the slave SSH process to one end and returns the other as
547               the first value ($in) and undef for the second ($out).
548
549               Example:
550
551                 my ($socket, undef, undef, $pid) = $ssh->open_ex({stdinout_socket => 1},
552                                                                  '/bin/netcat $dest');
553
554               See also "open2socket".
555
556           stdinout_dpipe => $cmd
557           stdinout_dpipe => \@cmd
558               Runs the given command locally attaching its stdio streams to
559               those of the remote SSH command. Conceptually it is equivalent
560               to the dpipe(1) shell command.
561
562           stderr_pipe => 1
563               Creates a new pipe and connects the writing side to the stderr
564               stream of the remote process. The reading side is returned as
565               the third value ($err).
566
567               Example:
568
569                 my $pid = $ssh->open_ex({stdinout_dpipe => 'vncviewer -stdio'},
570                                         x11vnc => '-inetd');
571
572           stderr_fh => $fh
573               Duplicates $fh and uses it as the stderr stream of the remote
574               process.
575
576           stderr_file => $filename
577               Opens the file of the given name and redirects stderr there.
578
579           stderr_to_stdout => 1
580               Makes stderr point to stdout.
581
582           tty => $bool
583               Tells "ssh" to allocate a pseudo-tty for the remote process. By
584               default, a tty is allocated if remote command stdin stream is
585               attached to a tty.
586
587               When this flag is set and stdin is not attached to a tty, the
588               ssh master and slave processes may generate spurious warnings
589               about failed tty operations. This is caused by a bug present in
590               older versions of OpenSSH.
591
592           close_slave_pty => 0
593               When a pseudo pty is used for the stdin stream, the slave side
594               is automatically closed on the parent process after forking the
595               ssh command.
596
597               This option disables that feature, so that the slave pty can be
598               accessed on the parent process as "$pty->slave". It will have
599               to be explicitly closed (see IO::Pty)
600
601           quote_args => $bool
602               See "Shell quoting" below.
603
604           remote_shell => $shell
605               Sets the remote shell. Allows one to change the argument
606               quoting mechanism in a per-command fashion.
607
608               This may be useful when interacting with a Windows machine
609               where argument parsing may be done at the command level in
610               custom ways.
611
612               Example:
613
614                 $ssh->system({remote_shell => 'MSWin'}, echo => $line);
615                 $ssh->system({remote_shell => 'MSCmd,MSWin'}, type => $file);
616
617           forward_agent => $bool
618               Enables/disables forwarding of the authentication agent.
619
620               This option can only be used when agent forwarding has been
621               previously requested on the constructor.
622
623           forward_X11 => $bool
624               Enables/disables forwarding of the X11 protocol.
625
626               This option can only be used when X11 forwarding has been
627               previously requested on the constructor.
628
629           ssh_opts => \@opts
630               List of extra options for the "ssh" command.
631
632               This feature should be used with care, as the given options are
633               not checked in any way by the module, and they could interfere
634               with it.
635
636           tunnel => $bool
637               Instead of executing a command in the remote host, this option
638               instruct Net::OpenSSH to create a TCP tunnel. The arguments
639               become the target IP and port or the remote path for an Unix
640               socket.
641
642               Example:
643
644                 my ($in, $out, undef, $pid) = $ssh->open_ex({tunnel => 1}, $IP, $port);
645                 my ($in, $out, undef, $pid) = $ssh->open_ex({tunnel => 1}, $socket_path);
646
647               See also "Tunnels".
648
649           subsystem => $bool
650               Request a connection to a SSH subsystem. The name of the
651               subsystem must be passed as an argument, as in the following
652               example:
653
654                 my $s = $ssh->open2socket({subsystem => 1}, 'netconf');
655
656           encoding => $encoding
657           argument_encoding => $encoding
658               Set encodings. See "Data encoding".
659
660           Usage example:
661
662             # similar to IPC::Open2 open2 function:
663             my ($in_pipe, $out_pipe, undef, $pid) =
664                 $ssh->open_ex( { stdin_pipe => 1,
665                                  stdout_pipe => 1 },
666                                @cmd )
667                 or die "open_ex failed: " . $ssh->error;
668             # do some IO through $in/$out
669             # ...
670             waitpid($pid);
671
672       setpgrp => 1
673           Calls "setpgrp" after forking the child process. As a result it
674           will not die when the user presses Ctrl+C at the console. See also
675           "setpgrp" in perlfunc.
676
677           Using this option without also setting "master_setpgrp" on the
678           constructor call is mostly useless as the signal will be delivered
679           to the master process and all the remote commands aborted.
680
681           This feature is experimental.
682
683       $ssh->system(\%opts, @cmd)
684           Runs the command @cmd on the remote machine.
685
686           Returns true on success, undef otherwise.
687
688           The error status is set to "OSSH_SLAVE_CMD_FAILED" when the remote
689           command exits with a non zero code (the code is available from $?,
690           see "$?" in perlvar).
691
692           Example:
693
694             $ssh->system('ls -R /')
695               or die "ls failed: " . $ssh->error";
696
697           As for "system" builtin, "SIGINT" and "SIGQUIT" signals are
698           blocked.  (see "system" in perlfunc). Also, setting $SIG{CHLD} to
699           "IGNORE" or to a custom signal handler will interfere with this
700           method.
701
702           Accepted options:
703
704           stdin_data => $input
705           stdin_data => \@input
706               Sends the given data through the stdin stream to the remote
707               process.
708
709               For example, the following code creates a file on the remote
710               side:
711
712                 $ssh->system({stdin_data => \@data}, "cat >/tmp/foo")
713                   or die "unable to write file: " . $ssh->error;
714
715           timeout => $timeout
716               The operation is aborted after $timeout seconds elapsed without
717               network activity.
718
719               See also "Timeouts".
720
721           async => 1
722               Does not wait for the child process to exit. The PID of the new
723               process is returned.
724
725               Note that when this option is combined with "stdin_data", the
726               given data will be transferred to the remote side before
727               returning control to the caller.
728
729               See also the "spawn" method documentation below.
730
731           stdin_fh => $fh
732           stdin_discard => $bool
733           stdout_fh => $fh
734           stdout_discard => $bool
735           stderr_fh => $fh
736           stderr_discard => $bool
737           stderr_to_stdout => $bool
738           stdinout_dpipe => $cmd
739           tty => $bool
740               See the "open_ex" method documentation for an explanation of
741               these options.
742
743           stdin_keep_open => $bool
744               When "stdin_data" is given, the module closes the stdin stream
745               once all the data has been sent. Unfortunately, some SSH buggy
746               servers fail to handle this event correctly and close the
747               channel prematurely.
748
749               As a workaround, when this flag is set the stdin is left open
750               until the remote process terminates.
751
752       $ok = $ssh->test(\%opts, @cmd);
753           Runs the given command and returns its success/failure exit status
754           as 1 or 0 respectively. Returns undef when something goes wrong in
755           the SSH layer.
756
757           Error status is not set to OSSH_SLAVE_CMD_FAILED when the remote
758           command exits with a non-zero code.
759
760           By default this method discards the remote command "stdout" and
761           "sterr" streams.
762
763           Usage example:
764
765             if ($ssh->test(ps => -C => $executable)) {
766               say "$executable is running on remote machine"
767             }
768             else {
769               die "something got wrong: ". $ssh->error if $ssh->error;
770
771               say "$executable is not running on remote machine"
772             }
773
774           This method support the same set of options as "system", except
775           "async" and "tunnel".
776
777       $output = $ssh->capture(\%opts, @cmd);
778       @output = $ssh->capture(\%opts, @cmd);
779           This method is conceptually equivalent to the perl backquote
780           operator (e.g. "`ls`"): it runs the command on the remote machine
781           and captures its output.
782
783           In scalar context returns the output as a scalar. In list context
784           returns the output broken into lines (it honors $/, see "$/" in
785           perlvar).
786
787           The exit status of the remote command is returned in $?.
788
789           When an error happens while capturing (for instance, the operation
790           times out), the partial captured output will be returned. Error
791           conditions have to be explicitly checked using the "error" method.
792           For instance:
793
794             my $output = $ssh->capture({ timeout => 10 },
795                                        "echo hello; sleep 20; echo bye");
796             $ssh->error and
797                 warn "operation didn't complete successfully: ". $ssh->error;
798             print $output;
799
800           Setting $SIG{CHLD} to a custom signal handler or to "IGNORE" will
801           interfere with this method.
802
803           Accepted options:
804
805           stdin_data => $input
806           stdin_data => \@input
807           stdin_keep_open => $bool
808               See the "system" method documentation for an explanation of
809               these options.
810
811           timeout => $timeout
812               See "Timeouts".
813
814           stdin_fh => $fh
815           stdin_discard => $bool
816           stderr_fh => $fh
817           stderr_discard => $bool
818           stderr_to_stdout => $bool
819           tty => $bool
820               See the "open_ex" method documentation for an explanation of
821               these options.
822
823       ($output, $errput) = $ssh->capture2(\%opts, @cmd)
824           captures the output sent to both stdout and stderr by @cmd on the
825           remote machine.
826
827           Setting $SIG{CHLD} to a custom signal handler or to "IGNORE" will
828           also interfere with this method.
829
830           The accepted options are:
831
832           stdin_data => $input
833           stdin_data => \@input
834           stdin_keep_open => $bool
835               See the "system" method documentation for an explanation of
836               these options.
837
838           timeout => $timeout
839               See "Timeouts".
840
841           stdin_fh => $fh
842           stdin_discard => $bool
843           tty => $bool
844               See the "open_ex" method documentation for an explanation of
845               these options.
846
847       ($in, $pid) = $ssh->pipe_in(\%opts, @cmd)
848           This method is similar to the following Perl "open" call
849
850             $pid = open $in, '|-', @cmd
851
852           but running @cmd on the remote machine (see "open" in perlfunc).
853
854           No options are currently accepted.
855
856           There is no need to perform a waitpid on the returned PID as it
857           will be done automatically by perl when $in is closed.
858
859           Example:
860
861             my ($in, $pid) = $ssh->pipe_in('cat >/tmp/fpp')
862                 or die "pipe_in failed: " . $ssh->error;
863             print $in $_ for @data;
864             close $in or die "close failed";
865
866       ($out, $pid) = $ssh->pipe_out(\%opts, @cmd)
867           Reciprocal to previous method, it is equivalent to
868
869             $pid = open $out, '-|', @cmd
870
871           running @cmd on the remote machine.
872
873           No options are currently accepted.
874
875       ($in, $out, $pid) = $ssh->open2(\%opts, @cmd)
876       ($pty, $pid) = $ssh->open2pty(\%opts, @cmd)
877       ($socket, $pid) = $ssh->open2socket(\%opts, @cmd)
878       ($in, $out, $err, $pid) = $ssh->open3(\%opts, @cmd)
879       ($pty, $err, $pid) = $ssh->open3pty(\%opts, @cmd)
880           Shortcuts around "open_ex" method.
881
882       $pid = $ssh->spawn(\%opts, @_)
883           Another "open_ex" shortcut, it launches a new remote process in the
884           background and returns the PID of the local slave SSH process.
885
886           At some later point in your script, "waitpid" should be called on
887           the returned PID in order to reap the slave SSH process.
888
889           For instance, you can run some command on several hosts in parallel
890           with the following code:
891
892             my %conn = map { $_ => Net::OpenSSH->new($_, async => 1) } @hosts;
893             my @pid;
894             for my $host (@hosts) {
895                 open my($fh), '>', "/tmp/out-$host.txt"
896                   or die "unable to create file: $!";
897                 push @pid, $conn{$host}->spawn({stdout_fh => $fh}, $cmd);
898             }
899
900             waitpid($_, 0) for @pid;
901
902           Note that "spawn" should not be used to start detached remote
903           processes that may survive the local program (see also the "FAQ"
904           about running remote processes detached).
905
906       ($socket, $pid) = $ssh->open_tunnel(\%opts, $dest_host, $port)
907       ($socket, $pid) = $ssh->open_tunnel(\%opts, $socket_path)
908           Similar to "open2socket", but instead of running a command, it
909           opens a TCP tunnel to the given address. See also "Tunnels".
910
911       $out = $ssh->capture_tunnel(\%opts, $dest_host, $port)
912       @out = $ssh->capture_tunnel(\%opts, $dest_host, $port)
913           Similar to "capture", but instead of running a command, it opens a
914           TCP tunnel.
915
916           Example:
917
918             $out = $ssh->capture_tunnel({stdin_data => join("\r\n",
919                                                             "GET / HTTP/1.0",
920                                                             "Host: www.perl.org",
921                                                             "", "") },
922                                         'www.perl.org', 80)
923
924           See also "Tunnels".
925
926       $ssh->scp_get(\%opts, $remote1, $remote2,..., $local_dir_or_file)
927       $ssh->scp_put(\%opts, $local, $local2,..., $remote_dir_or_file)
928           These two methods are wrappers around the "scp" command that allow
929           transfers of files to/from the remote host using the existing SSH
930           master connection.
931
932           When transferring several files, the target argument must point to
933           an existing directory. If only one file is to be transferred, the
934           target argument can be a directory or a file name or can be
935           omitted. For instance:
936
937             $ssh->scp_get({glob => 1}, '/var/tmp/foo*', '/var/tmp/bar*', '/tmp');
938             $ssh->scp_put('/etc/passwd');
939
940           Both "scp_get" and "scp_put" methods return a true value when all
941           the files are transferred correctly, otherwise they return undef.
942
943           Accepted options:
944
945           quiet => 0
946               By default, "scp" is called with the quiet flag "-q" enabled in
947               order to suppress progress information. This option allows one
948               to re-enable the progress indication bar.
949
950           verbose => 1
951               Calls "scp" with the "-v" flag.
952
953           recursive => 1
954               Copies files and directories recursively.
955
956           glob => 1
957               Enables expansion of shell metacharacters in the sources list
958               so that wildcards can be used to select files.
959
960           glob_flags => $flags
961               Second argument passed to File::Glob::bsd_glob function. Only
962               available for "scp_put" method.
963
964           copy_attrs => 1
965               Copies modification and access times and modes from the
966               original files.
967
968           bwlimit => $Kbits
969               Limits the used bandwidth, specified in Kbit/s.
970
971           timeout => $secs
972               The transfer is aborted if the connection does not finish
973               before the given timeout elapses. See also "Timeouts".
974
975           async => 1
976               Does not wait for the "scp" command to finish. When this option
977               is used, the method returns the PID of the child "scp" process.
978
979               For instance, it is possible to transfer files to several hosts
980               in parallel as follows:
981
982                 use Errno;
983                 my (%pid, %ssh);
984                 for my $host (@hosts) {
985                   $ssh{$host} = Net::OpenSSH->new($host, async => 1);
986                 }
987                 for my $host (@hosts) {
988                   $pid{$host} = $ssh{$host}->scp_put({async => 1}, $local_fn, $remote_fn)
989                     or warn "scp_put to $host failed: " . $ssh{$host}->error . "\n";
990                 }
991                 for my $host (@hosts) {
992                   if (my $pid = $pid{$host}) {
993                     if (waitpid($pid, 0) > 0) {
994                       my $exit = ($? >> 8);
995                       $exit and warn "transfer of file to $host failed ($exit)\n";
996                     }
997                     else {
998                       redo if ($! == EINTR);
999                       warn "waitpid($pid) failed: $!\n";
1000                     }
1001                   }
1002                 }
1003
1004           stdout_fh => $fh
1005           stderr_fh => $fh
1006           stderr_to_stdout => 1
1007               These options are passed unchanged to method "open_ex",
1008               allowing capture of the output of the "scp" program.
1009
1010               Note that "scp" will not generate progress reports unless its
1011               stdout stream is attached to a tty.
1012
1013           ssh_opts => \@opts
1014               List of extra options for the "ssh" command.
1015
1016               This feature should be used with care, as the given options are
1017               not checked in any way by the module, and they could interfere
1018               with it.
1019
1020       $ssh->rsync_get(\%opts, $remote1, $remote2,..., $local_dir_or_file)
1021       $ssh->rsync_put(\%opts, $local1, $local2,..., $remote_dir_or_file)
1022           These methods use "rsync" over SSH to transfer files from/to the
1023           remote machine.
1024
1025           They accept the same set of options as the "scp" ones.
1026
1027           Any unrecognized option will be passed as an argument to the
1028           "rsync" command (see rsync(1)). Underscores can be used instead of
1029           dashes in "rsync" option names.
1030
1031           For instance:
1032
1033             $ssh->rsync_get({exclude => '*~',
1034                              verbose => 1,
1035                              safe_links => 1},
1036                             '/remote/dir', '/local/dir');
1037
1038       $sftp = $ssh->sftp(%sftp_opts)
1039           Creates a new Net::SFTP::Foreign object for SFTP interaction that
1040           runs through the ssh master connection.
1041
1042       @call = $ssh->make_remote_command(\%opts, @cmd)
1043       $call = $ssh->make_remote_command(\%opts, @cmd)
1044           This method returns the arguments required to execute a command on
1045           the remote machine via SSH. For instance:
1046
1047             my @call = $ssh->make_remote_command(ls => "/var/log");
1048             system @call;
1049
1050           In scalar context, returns the arguments quoted and joined into one
1051           string:
1052
1053             my $remote = $ssh->make_remote_comand("cd /tmp/ && tar xf -");
1054             system "tar cf - . | $remote";
1055
1056           The options accepted are as follows:
1057
1058           tty => $bool
1059               Enables/disables allocation of a tty on the remote side.
1060
1061           forward_agent => $bool
1062               Enables/disables forwarding of authentication agent.
1063
1064               This option can only be used when agent forwarding has been
1065               previously requested on the constructor.
1066
1067           tunnel => 1
1068               Return a command to create a connection to some TCP server
1069               reachable from the remote host. In that case the arguments are
1070               the destination address and port. For instance:
1071
1072                 $cmd = $ssh->make_remote_command({tunnel => 1}, $host, $port);
1073
1074           subsystem => 1
1075               Return a command for invoking a SSH subsystem (i.e. SFTP or
1076               netconf). In that case the only argument is the subsystem name.
1077
1078       $ssh->wait_for_master($async)
1079           When the connection has been established by calling the constructor
1080           with the "async" option, this call allows one to advance the
1081           process.
1082
1083           If $async is true, it will perform any work that can be done
1084           immediately without waiting (for instance, entering the password or
1085           checking for the existence of the multiplexing socket) and then
1086           return. If a false value is given, it will finalize the connection
1087           process and wait until the multiplexing socket is available.
1088
1089           It returns a true value after the connection has been successfully
1090           established. False is returned if the connection process fails or
1091           if it has not yet completed (then, the "error" method can be used
1092           to distinguish between both cases).
1093
1094           From version 0.64 upwards, undef is returned when the master is
1095           still in an unstable state (login, killing, etc.) and 0 when it is
1096           in a stable state (running, stopped or gone).
1097
1098       $ssh->check_master
1099           This method runs several checks to ensure that the master
1100           connection is still alive.
1101
1102       $ssh->shell_quote(@args)
1103           Returns the list of arguments quoted so that they will be restored
1104           to their original form when parsed by the remote shell.
1105
1106           In scalar context returns the list of arguments quoted and joined.
1107
1108           Usually this task is done automatically by the module. See "Shell
1109           quoting" below.
1110
1111           This method can also be used as a class method.
1112
1113           Example:
1114
1115             my $quoted_args = Net::OpenSSH->shell_quote(@args);
1116             system('ssh', '--', $host, $quoted_args);
1117
1118       $ssh->shell_quote_glob(@args)
1119           This method is like the previous "shell_quote" but leaves wildcard
1120           characters unquoted.
1121
1122           It can be used as a class method also.
1123
1124       $ssh->set_expand_vars($bool)
1125           Enables/disables variable expansion feature (see "Variable
1126           expansion").
1127
1128       $ssh->get_expand_vars
1129           Returns current state of variable expansion feature.
1130
1131       $ssh->set_var($name, $value)
1132       $ssh->get_var($name, $value)
1133           These methods allow one to change and to retrieve the value of the
1134           given name.
1135
1136       $ssh->get_master_pid
1137           Returns the PID of the master SSH process
1138
1139       $ssh->master_exited
1140           This methods allows one to tell the module that the master process
1141           has exited when we get its PID from some external wait or waitpid
1142           call. For instance:
1143
1144             my $ssh = Net::OpenSSH->new('foo', async => 1);
1145
1146             # create new processes
1147             # ...
1148
1149             # rip them...
1150             my $master_pid = $ssh->master_pid;
1151             while ((my $pid = wait) > 0) {
1152               if ($pid == $master_pid) {
1153                 $ssh->master_exited;
1154               }
1155             }
1156
1157           If your program rips the master process and this method is not
1158           called, the OS could reassign the PID to a new unrelated process
1159           and the module would try to kill it at object destruction time.
1160
1161       $ssh->disconnect($async)
1162           Shuts down the SSH connection.
1163
1164           Usually, you don't need to call this method explicitly, but just
1165           let the Net::OpenSSH object go out of scope.
1166
1167           If "async" is true, it doesn't wait for the SSH connection to
1168           terminate. In that case, "wait_for_master" must be called
1169           repeatedly until the shutdown sequence terminates (See the
1170           "AnyEvent" integration section below).
1171
1172       $ssh->restart($async)
1173           Restarts the SSH session closing any open connection and creating a
1174           new one. Any open channel would also be killed.
1175
1176           Note that calling this method may request again the password or
1177           passphrase from the user.
1178
1179           In asynchronous mode, this method requires the connection to be
1180           terminated before it gets called. Afterwards, "wait_for_master"
1181           should be called repeaptly until the new connection is stablished.
1182
1183             my $async = 1;
1184             $ssh->disconnect($async);
1185             while (1) {
1186               defined $ssh->wait_for_master($async) # returns 0 when the
1187                                                     # disconnect process
1188                                                     # finishes
1189                 and last;
1190               do_something_else();
1191             }
1192             $ssh->restart($async);
1193             while (1) {
1194               defined $ssh->wait_for_master($async)
1195                 and last;
1196               do_somethin_else();
1197             }
1198
1199       $pid = $ssh->sshfs_import(\%opts, $remote_fs, $local_mnt_point)
1200       $pid = $ssh->sshfs_export(\%opts, $local_fs, $remote_mnt_point)
1201           These methods use sshfs(1) to import or export a file system
1202           through the SSH connection.
1203
1204           They return the $pid of the "sshfs" process or of the slave "ssh"
1205           process used to proxy it. Killing that process unmounts the file
1206           system, though, it may be probably better to use fusermount(1).
1207
1208           The options accepted are as follows:
1209
1210           ssh_opts => \@ssh_opts
1211               Options passed to the slave "ssh" process.
1212
1213           sshfs_opts => \@sshfs_opts
1214               Options passed to the "sshfs" command. For instance, to mount
1215               the file system in read-only mode:
1216
1217                 my $pid = $ssh->sshfs_export({sshfs_opts => [-o => 'ro']},
1218                                              "/", "/mnt/foo");
1219
1220           Note that this command requires a recent version of "sshfs" to work
1221           (at the time of writing, it requires the yet unreleased version
1222           available from the FUSE git repository!).
1223
1224           See also the sshfs(1) man page and the "sshfs" and FUSE web sites
1225           at <https://github.com/libfuse/sshfs> and
1226           <https://github.com/libfuse/libfuse> respectively.
1227
1228       $or = $ssh->object_remote(@args)
1229           Returns an Object::Remote::Connection instance running on top of
1230           the Net::OpenSSH connection.
1231
1232           Example:
1233
1234              my $or = $ssh->object_remote;
1235              my $hostname = Sys::Hostname->can::on($or, 'hostname');
1236              say $hostname->();
1237
1238           See also Object::Remote.
1239
1240       $any = $ssh->any(%opts)
1241           Wraps the current object inside a Net::SSH::Any one.
1242
1243           Example:
1244
1245             my $any = $ssh->any;
1246             my $content = $any->scp_get_content("my-file.txt");
1247
1248       $pid = $ssh->disown_master
1249           Under normal operation Net::OpenSSH controls the life-time of the
1250           master "ssh" process and when the object is destroyed the master
1251           process and any connection running over it are terminated.
1252
1253           In some (rare) cases, it is desirable to let the master process and
1254           all the running connections survive. Calling this method does just
1255           that, it tells Net::OpenSSH object that the master process is not
1256           its own anymore.
1257
1258           The return value is the PID of the master process.
1259
1260           Note also that disowning the master process does not affect the
1261           operation of the module in any other regard.
1262
1263           For instance:
1264
1265             # See examples/sshfs_mount.pl for a working program
1266             my $ssh = Net::OpenSSH->new($host);
1267             my $sshfs_pid = $ssh->sshfs_import("/home/foo", "my-remote-home");
1268             $ssh->disown_master;
1269             $ssh->stop; # tells the master to stop accepting requests
1270             exit(0);
1271
1272   Shell quoting
1273       By default, when invoking remote commands, this module tries to mimic
1274       perl "system" builtin in regard to argument processing. Quoting
1275       "system" in perlfunc:
1276
1277         Argument processing varies depending on the number of arguments.  If
1278         there is more than one argument in LIST, or if LIST is an array with
1279         more than one value, starts the program given by the first element
1280         of the list with arguments given by the rest of the list.  If there
1281         is only one scalar argument, the argument is checked for shell
1282         metacharacters, and if there are any, the entire argument is passed
1283         to the system's command shell for parsing (this is "/bin/sh -c" on
1284         Unix platforms, but varies on other platforms).
1285
1286       Take for example Net::OpenSSH "system" method:
1287
1288         $ssh->system("ls -l *");
1289         $ssh->system('ls', '-l', '/');
1290
1291       The first call passes the argument unchanged to ssh and it is executed
1292       in the remote side through the shell which interprets metacharacters.
1293
1294       The second call escapes any shell metacharacters so that, effectively,
1295       it is equivalent to calling the command directly and not through the
1296       shell.
1297
1298       Under the hood, as the Secure Shell protocol does not provide for this
1299       mode of operation and always spawns a new shell where it runs the given
1300       command, Net::OpenSSH quotes any shell metacharacters in the command
1301       list.
1302
1303       All the methods that invoke a remote command (system, open_ex, etc.)
1304       accept the option "quote_args" that allows one to force/disable shell
1305       quoting.
1306
1307       For instance:
1308
1309         $ssh->system({quote_args => 1}, "/path with spaces/bin/foo");
1310
1311       will correctly handle the spaces in the program path.
1312
1313       The shell quoting mechanism implements some extensions (for instance,
1314       performing redirections to /dev/null on the remote side) that can be
1315       disabled with the option "quote_args_extended":
1316
1317         $ssh->system({ stderr_discard => 1,
1318                        quote_args => 1, quote_args_extended => 0 },
1319                      @cmd);
1320
1321       The option "quote_args" can also be used to disable quoting when more
1322       than one argument is passed. For instance, to get some pattern expanded
1323       by the remote shell:
1324
1325         $ssh->system({quote_args => 0}, 'ls', '-l', "/tmp/files_*.dat");
1326
1327       The method "shell_quote" can be used to selectively quote some
1328       arguments and leave others untouched:
1329
1330         $ssh->system({quote_args => 0},
1331                      $ssh->shell_quote('ls', '-l'),
1332                      "/tmp/files_*.dat");
1333
1334       When the glob option is set in "scp" and "rsync" file transfer methods,
1335       an alternative quoting method which knows about file wildcards and
1336       passes them unquoted is used. The set of wildcards recognized currently
1337       is the one supported by bash(1).
1338
1339       Another way to selectively use quote globing or fully disable quoting
1340       for some specific arguments is to pass them as scalar references or
1341       double scalar references respectively. In practice, that means
1342       prepending them with one or two backslashes. For instance:
1343
1344         # quote the last argument for globing:
1345         $ssh->system('ls', '-l', \'/tmp/my files/filed_*dat');
1346
1347         # append a redirection to the remote command
1348         $ssh->system('ls', '-lR', \\'>/tmp/ls-lR.txt');
1349
1350         # expand remote shell variables and glob in the same command:
1351         $ssh->system('tar', 'czf', \\'$HOME/out.tgz', \'/var/log/server.*.log');
1352
1353       As shell quoting is a tricky matter, I expect bugs to appear in this
1354       area. You can see how "ssh" is called, and the quoting used setting the
1355       following debug flag:
1356
1357         $Net::OpenSSH::debug |= 16;
1358
1359       By default, the module assumes the remote shell is some variant of a
1360       POSIX or Bourne shell ("bash", "dash", "ksh", etc.). If this is not the
1361       case, the construction option "remote_shell" can be used to select an
1362       alternative quoting mechanism.
1363
1364       For instance:
1365
1366         $ssh = Net::OpenSSH->new($host, remote_shell => 'csh');
1367         $ssh->system(echo => "hard\n to\n  quote\n   argument!");
1368
1369       Currently there are quoters available for POSIX (Bourne) compatible
1370       shells, "csh" and the two Windows variants "MSWin" (for servers using
1371       Win32::CreateProcess, see Net::OpenSSH::ShellQuoter::MSWin) and "MSCmd"
1372       (for servers using "cmd.exe", see Net::OpenSSH::ShellQuoter::MSCmd).
1373
1374       In any case, you can always do the quoting yourself and pass the quoted
1375       remote command as a single string:
1376
1377         # for VMS
1378         $ssh->system('DIR/SIZE NFOO::USERS:[JSMITH.DOCS]*.TXT;0');
1379
1380       Note that the current quoting mechanism does not handle possible
1381       aliases defined by the remote shell. In that case, to force execution
1382       of the command instead of the alias, the full path to the command must
1383       be used.
1384
1385   Timeouts
1386       In order to stop remote processes when they timeout, the ideal approach
1387       would be to send them signals through the SSH connection as specified
1388       by the protocol standard.
1389
1390       Unfortunately OpenSSH does not implement that feature so Net::OpenSSH
1391       has to use other imperfect approaches:
1392
1393       ā€¢   close slave I/O streams
1394
1395           Closing the STDIN and STDOUT streams of the unresponsive remote
1396           process will effectively deliver a SIGPIPE when it tries to access
1397           any of them.
1398
1399           Remote processes may not access STDIN or STDOUT and even then,
1400           Net::OpenSSH can only close these channels when it is capturing
1401           them, so this approach does not always work.
1402
1403       ā€¢   killing the local SSH slave process
1404
1405           This action may leave the remote process running, creating a remote
1406           orphan so Net::OpenSSH does not use it unless the construction
1407           option "kill_ssh_on_timeout" is set.
1408
1409       Luckily, future versions of OpenSSH will support signaling remote
1410       processes via the mux channel.
1411
1412   Variable expansion
1413       The variable expansion feature allows one to define variables that are
1414       expanded automatically inside command arguments and file paths.
1415
1416       This feature is disabled by default. It is intended to be used with
1417       Net::OpenSSH::Parallel and other similar modules.
1418
1419       Variables are delimited by a pair of percent signs ("%"), for instance
1420       "%HOST%". Also, two consecutive percent signs are replaced by a single
1421       one.
1422
1423       The special variables "HOST", "USER" and "PORT" are maintained
1424       internally by the module and take the obvious values.
1425
1426       Variable expansion is performed before shell quoting (see "Shell
1427       quoting").
1428
1429       Some usage example:
1430
1431         my $ssh = Net::OpenSSH->new('server.foo.com', expand_vars => 1);
1432         $ssh->set_var(ID => 42);
1433         $ssh->system("ls >/tmp/ls.out-%HOST%-%ID%");
1434
1435       will redirect the output of the "ls" command to
1436       "/tmp/ls.out-server.foo.com-42" on the remote host.
1437
1438   Tunnels
1439       Besides running commands on the remote host, Net::OpenSSH also allows
1440       one to tunnel TCP connections to remote machines reachable from the SSH
1441       server.
1442
1443       That feature is made available through the "tunnel" option of the
1444       "open_ex" method, and also through wrapper methods "open_tunnel" and
1445       "capture_tunnel" and most others where it makes sense.
1446
1447       Example:
1448
1449         $ssh->system({tunnel => 1,
1450                       stdin_data => "GET / HTTP/1.0\r\n\r\n",
1451                       stdout_file => "/tmp/$server.res"},
1452                      $server, 80)
1453             or die "unable to retrieve page: " . $ssh->error;
1454
1455       or capturing the output of several requests in parallel:
1456
1457         my @pids;
1458         for (@servers) {
1459           my $pid = $ssh->spawn({tunnel => 1,
1460                                  stdin_file => "/tmp/request.req",
1461                                  stdout_file => "/tmp/$_.res"},
1462                                 $_, 80);
1463           if ($pid) {
1464             push @pids, $pid;
1465           }
1466           else {
1467             warn "unable to spawn tunnel process to $_: " . $ssh->error;
1468           }
1469         }
1470         waitpid ($_, 0) for (@pids);
1471
1472       Under the hood, in order to create a tunnel, a new "ssh" process is
1473       spawned with the option "-W${address}:${port}" (available from OpenSSH
1474       5.4 and upwards) making it redirect its stdio streams to the remote
1475       given address. Unlike when "ssh" "-L" options is used to create
1476       tunnels, no TCP port is opened on the local machine at any time so this
1477       is a perfectly secure operation.
1478
1479       The PID of the new process is returned by the named methods. It must be
1480       reaped once the pipe or socket handlers for the local side of the
1481       tunnel have been closed.
1482
1483       OpenSSH 5.4 or later is required for the tunnels functionality to work.
1484       Also, note that tunnel forwarding may be administratively forbidden at
1485       the server side (see sshd(8) and sshd_config(5) or the documentation
1486       provided by your SSH server vendor).
1487
1488       Tunnels targeting UNIX sockets
1489
1490       When connecting to hosts running a recent version of OpenSSH sshd, it
1491       is also possible to open connections targeting Unix sockets.
1492
1493       For instance:
1494
1495         my $response = $ssh->capture({tunnel => 1, stdin_data => $request },
1496                                      "/tmp/socket-foo");
1497
1498       Currently, this feature requires a patched OpenSSH ssh client. The
1499       patch is available as
1500       "patches/openssh-fwd-stdio-to-streamlocal-1.patch".
1501
1502       Port forwarding
1503
1504       Net::OpenSSH does not offer direct support for handling port
1505       forwardings between server and client. But that can be done easily
1506       anyway passing custom SSH options to its methods.
1507
1508       For instance, tunnel creation options can be passed to the constructor:
1509
1510         my $ssh = Net::OpenSSH->new(...
1511                           master_opts => -Llocalhost:1234:localhost:3306');
1512
1513       The port forwardings can also be changed for a running SSH connection
1514       using a Control command:
1515
1516           # setting up a tunnel:
1517           $ssh->system({ssh_opts => ['-O','forward',
1518                                      '-L127.0.0.1:12345:127.0.0.1:3306']});
1519
1520           # canceling it:
1521           $ssh->system({ssh_opts => ['-O', 'cancel',
1522                                      '-L127.0.0.1:12345:127.0.0.1:3306']});
1523
1524   Data encoding
1525       Net::OpenSSH has some support for transparently converting the data
1526       send or received from the remote server to Perl internal unicode
1527       representation.
1528
1529       The methods supporting that feature are those that move data from/to
1530       Perl data structures (e.g. "capture", "capture2", "capture_tunnel" and
1531       methods supporting the "stdin_data" option). Data accessed through
1532       pipes, sockets or redirections is not affected by the encoding options.
1533
1534       It is also possible to set the encoding of the command and arguments
1535       passed to the remote server on the command line.
1536
1537       By default, if no encoding option is given on the constructor or on the
1538       method calls, Net::OpenSSH will not perform any encoding
1539       transformation, effectively processing the data as "latin1".
1540
1541       When data can not be converted between the Perl internal representation
1542       and the selected encoding inside some Net::OpenSSH method, it will fail
1543       with an "OSSH_ENCODING_ERROR" error.
1544
1545       The supported encoding options are as follows:
1546
1547       stream_encoding => $encoding
1548           sets the encoding of the data send and received on capture methods.
1549
1550       argument_encoding => $encoding
1551           sets the encoding of the command line arguments
1552
1553       encoding => $encoding
1554           sets both "argument_encoding" and "stream_encoding".
1555
1556       The constructor also accepts "default_encoding",
1557       "default_stream_encoding" and "default_argument_encoding" that set the
1558       defaults.
1559
1560   Diverting "new"
1561       When a code ref is installed at $Net::OpenSSH::FACTORY, calls to new
1562       will be diverted through it.
1563
1564       That feature can be used to transparently implement connection caching,
1565       for instance:
1566
1567         my $old_factory = $Net::OpenSSH::FACTORY;
1568         my %cache;
1569
1570         sub factory {
1571           my ($class, %opts) = @_;
1572           my $signature = join("\0", $class, map { $_ => $opts{$_} }, sort keys %opts);
1573           my $old = $cache{signature};
1574           return $old if ($old and $old->error != OSSH_MASTER_FAILED);
1575           local $Net::OpenSSH::FACTORY = $old_factory;
1576           $cache{$signature} = $class->new(%opts);
1577         }
1578
1579         $Net::OpenSSH::FACTORY = \&factory;
1580
1581       ... and I am sure it can be abused in several other ways!
1582

3rd PARTY MODULE INTEGRATION

1584   Expect
1585       Sometimes you would like to use Expect to control some program running
1586       in the remote host. You can do it as follows:
1587
1588         my ($pty, $pid) = $ssh->open2pty(@cmd)
1589             or die "unable to run remote command @cmd";
1590         my $expect = Expect->init($pty);
1591
1592       Then, you will be able to use the new Expect object in $expect as
1593       usual.
1594
1595   Net::Telnet
1596       This example is adapted from Net::Telnet documentation:
1597
1598         my ($pty, $pid) = $ssh->open2pty({stderr_to_stdout => 1})
1599           or die "unable to start remote shell: " . $ssh->error;
1600         my $telnet = Net::Telnet->new(-fhopen => $pty,
1601                                       -prompt => '/.*\$ $/',
1602                                       -telnetmode => 0,
1603                                       -cmd_remove_mode => 1,
1604                                       -output_record_separator => "\r");
1605
1606         $telnet->waitfor(-match => $telnet->prompt,
1607                          -errmode => "return")
1608           or die "login failed: " . $telnet->lastline;
1609
1610         my @lines = $telnet->cmd("who");
1611
1612         ...
1613
1614         $telnet->close;
1615         waitpid($pid, 0);
1616
1617   mod_perl and mod_perl2
1618       mod_perl and mod_perl2 tie STDIN and STDOUT to objects that are not
1619       backed up by real file descriptors at the operating system level.
1620       Net::OpenSSH will fail if any of these handles is used explicitly or
1621       implicitly when calling some remote command.
1622
1623       The work-around is to redirect them to "/dev/null" or to some file:
1624
1625         open my $def_in, '<', '/dev/null' or die "unable to open /dev/null";
1626         my $ssh = Net::OpenSSH->new($host,
1627                                     default_stdin_fh => $def_in);
1628
1629         my $out = $ssh->capture($cmd1);
1630         $ssh->system({stdout_discard => 1}, $cmd2);
1631         $ssh->system({stdout_to_file => '/tmp/output'}, $cmd3);
1632
1633       Also, note that from a security stand point, running "ssh" from inside
1634       the web server process is not a great idea. An attacker exploiting some
1635       Apache bug would be able to access the SSH keys and passwords and gain
1636       unlimited access to the remote systems.
1637
1638       If you can, use a queue (as TheSchwartz) or any other mechanism to
1639       execute the ssh commands from another process running under a different
1640       user account.
1641
1642       At a minimum, ensure that "~www-data/.ssh" (or similar) is not
1643       accessible through the web server!
1644
1645   Net::SFTP::Foreign
1646       See method "sftp".
1647
1648   Net::SSH::Any
1649       See method "any".
1650
1651   Object::Remote
1652       See method "object_remote".
1653
1654   AnyEvent (and similar frameworks)
1655       Net::OpenSSH provides all the functionality required to be integrated
1656       inside event oriented programming framework such as AnyEvent or
1657       IO::Async in the following way:
1658
1659       1. Create a disconnected Net::OpenSSH object:
1660               my $ssh = Net::OpenSSH->new($host, async => 1, ...);
1661
1662       2. Let the object connect to the remote host:
1663           Use a timer to call the "wait_for_master" method in async mode
1664           repeatedly until it returns a true value indicating success.
1665
1666           Also, the object error state needs to be checked after every call
1667           in order to detect failed connections. For instance:
1668
1669             my $ssh = Net::OpenSSH->new(..., async => 1);
1670             my $w;
1671             $w = AE::timer 0.1, 0.1, sub {
1672               if ($ssh->wait_for_master(1)) {
1673                 # the connection has been established!
1674                 # remote commands can be run now
1675                 undef $w;
1676                 on_ssh_success(...);
1677               }
1678               elsif ($ssh->error) {
1679                 # connection can not be established
1680                 undef $w;
1681                 on_ssh_failure(...);
1682               }
1683             }
1684
1685       3. Use the event framework to launch the remote processes:
1686           Call Net::OpenSSH "make_remote_command" to construct commands which
1687           can be run using the framework regular facilities for launching
1688           external commands.
1689
1690           Error checking should also be performed at this point because the
1691           SSH connection could be broken.
1692
1693           For instance:
1694
1695             if (defined(my $cmd = $ssh->make_remote_command(echo => 'hello!')) {
1696               AnyEvent::Util::run_cmd($cmd, %run_cmd_opts);
1697             }
1698             else {
1699               # something went wrong!
1700             }
1701
1702           Alternatively, any of the "open*" methods provided by Net::OpenSSH
1703           could also be used to launch remote commands.
1704
1705       4. When finished, disconnect asynchronously
1706           After initiating an asynchronous disconnect with disconnect(1),
1707           repeatedly call "wait_for_master" until you get a defined but false
1708           value:
1709
1710             $ssh->disconnect(1);
1711
1712             my $w; $w = AE::timer 0.1, 0.1, sub {
1713               my $res = $ssh->wait_for_master(1);
1714
1715               if (defined $res && !$res) {
1716                 undef $w;
1717                 undef $ssh;
1718               }
1719             };
1720
1721           Be careful not to let the $ssh object go out of scope until the
1722           disconnection has finished, otherwise its destructor will wait and
1723           block your program until the disconnection has completed.
1724
1725   Other modules
1726       CPAN contains several modules that rely on SSH to perform their duties
1727       as for example IPC::PerlSSH or GRID::Machine.
1728
1729       Often, it is possible to instruct them to go through a Net::OpenSSH
1730       multiplexed connection employing some available constructor option. For
1731       instance:
1732
1733         use Net::OpenSSH;
1734         use IPC::PerlIPC;
1735         my $ssh = Net::OpenSSH->new(...);
1736         $ssh->error and die "unable to connect to remote host: " . $ssh->error;
1737         my @cmd = $ssh->make_remote_command('/usr/bin/perl');
1738         my $ipc = IPC::PerlSSH->new(Command => \@cmd);
1739         my @r = $ipc->eval('...');
1740
1741       or...
1742
1743         use GRID::Machine;
1744         ...
1745         my @cmd = $ssh->make_remote_command('/usr/bin/perl');
1746         my $grid = GRID::Machine->new(command => \@cmd);
1747         my $r = $grid->eval('print "hello world!\n"');
1748
1749       In other cases, some kind of plugin mechanism is provided by the 3rd
1750       party modules to allow for different transports. The method "open2" may
1751       be used to create a pair of pipes for transport in these cases.
1752

TROUBLESHOOTING

1754       Usually, Net::OpenSSH works out of the box, but when it fails, some
1755       users have a hard time finding the cause of the problem. This mini
1756       troubleshooting guide should help you to find and solve it.
1757
1758       1 - check the error message
1759           Add in your script, after the Net::OpenSSH constructor call, an
1760           error check:
1761
1762             $ssh = Net::OpenSSH->new(...);
1763             $ssh->error and die "SSH connection failed: " . $ssh->error;
1764
1765           The error message will tell what has gone wrong.
1766
1767       2 - Check the connection parameters
1768           Believe it or not, passing bad parameters to Net::OpenSSH turns to
1769           be one of the top causes of failures so check that you are using
1770           the right parameters.
1771
1772           Specifically, if you are obtaining them from the outside, ensure
1773           that they don't have extra spaces or new lines attached (do you
1774           need to "chomp"?).
1775
1776           Passwords and URIs may contain "$" or "@" characters. If you have
1777           then hardcoded in your script, check that those are quoted properly
1778           (and BTW, use "strict").
1779
1780       3 - OpenSSH version
1781           Ensure that you have a version of "ssh" recent enough:
1782
1783             $ ssh -V
1784             OpenSSH_5.1p1 Debian-5, OpenSSL 0.9.8g 19 Oct 2007
1785
1786           OpenSSH version 4.1 was the first to support the multiplexing
1787           feature and is the minimal required by the module to work. I advise
1788           you to use the latest OpenSSH (currently 7.5).
1789
1790           The "ssh_cmd" constructor option lets you select the "ssh" binary
1791           to use. For instance:
1792
1793             $ssh = Net::OpenSSH->new($host,
1794                                      ssh_cmd => "/opt/OpenSSH/5.8/bin/ssh")
1795
1796           Some hardware vendors (e.g. Sun, err... Oracle) include custom
1797           versions of OpenSSH bundled with the operating system. In
1798           principle, Net::OpenSSH should work with these SSH clients as long
1799           as they are derived from some version of OpenSSH recent enough.
1800           Anyway, my advise is to use the real OpenSSH software if you can!
1801
1802       4 - run ssh from the command line
1803           Check you can connect to the remote host using the same parameters
1804           you are passing to Net::OpenSSH. In particular, ensure that you are
1805           running "ssh" as the same local user.
1806
1807           If you are running your script from a web server, the user would
1808           probably be "www", "apache" or something alike.
1809
1810           Common problems are:
1811
1812           ā€¢   Remote host public key not present in known_hosts file.
1813
1814               The SSH protocol uses public keys to identify the remote hosts
1815               so that they can not be supplanted by some malicious third
1816               parties.
1817
1818               For OpenSSH, usually the server public key is stored in
1819               "/etc/ssh/ssh_host_dsa_key.pub" or in
1820               "/etc/ssh/ssh_host_rsa_key.pub" and that key should be copied
1821               into the "~/.ssh/known_hosts" file in the local machine (other
1822               SSH implementations may use other file locations).
1823
1824               Maintaining the server keys when several hosts and clients are
1825               involved may be somewhat inconvenient, so most SSH clients, by
1826               default, when a new connection is established to a host whose
1827               key is not in the "known_hosts" file, show the key and ask the
1828               user if he wants the key copied there.
1829
1830           ā€¢   Wrong remote host public key in known_hosts file.
1831
1832               This is another common problem that happens when some server is
1833               replaced or reinstalled from scratch and its public key changes
1834               becoming different to that installed on the "known_hosts" file.
1835
1836               The easiest way to solve that problem is to remove the old key
1837               from the "known_hosts" file by hand using any editor and then
1838               to connect to the server replying "yes" when asked to save the
1839               new key.
1840
1841           ā€¢   Wrong permissions for the "~/.ssh" directory or its contents.
1842
1843               OpenSSH client performs several checks on the access
1844               permissions of the "~/.ssh" directory and its contents and
1845               refuses to use them when misconfigured. See the FILES section
1846               from the ssh(1) man page.
1847
1848           ā€¢   Incorrect settings for password or public key authentication.
1849
1850               Check that you are using the right password or that the user
1851               public key is correctly installed on the server.
1852
1853       5 - security checks on the multiplexing socket
1854           Net::OpenSSH performs some security checks on the directory where
1855           the multiplexing socket is going to be placed to ensure that it can
1856           not be accessed by other users.
1857
1858           The default location for the multiplexing socket is under
1859           "~/.libnet-openssh-perl". It can be changed using the "ctl_dir" and
1860           "ctl_path" constructor arguments.
1861
1862           The requirements for that directory and all its parents are:
1863
1864           ā€¢   They have to be owned by the user executing the script or by
1865               root
1866
1867           ā€¢   Their permission masks must be 0755 or more restrictive, so
1868               nobody else has permissions to perform write operations on
1869               them.
1870
1871           The constructor option "strict_mode" disables these security
1872           checks, but you should not use it unless you understand its
1873           implications.
1874
1875       6 - file system must support sockets
1876           Some file systems (as for instance FAT or AFS) do not support
1877           placing sockets inside them.
1878
1879           Ensure that the "ctl_dir" path does not lay into one of those file
1880           systems.
1881

DEBUGGING

1883       Debugging of Net::OpenSSH internals is controlled through the variable
1884       $Net::OpenSSH::debug. Every bit of this variable activates debugging of
1885       some subsystem as follows:
1886
1887       bit 1 - errors
1888           Dumps changes on the internal object attribute where errors are
1889           stored.
1890
1891       bit 2 - ctl_path
1892           Dumps information about ctl_path calculation and the tests
1893           performed on that directory in order to decide if it is secure to
1894           place the multiplexing socket inside.
1895
1896       bit 4 - connecting
1897           Dumps information about the establishment of new master
1898           connections.
1899
1900       bit 8 - commands and arguments
1901           Dumps the command and arguments for every system/exec call.
1902
1903       bit 16 - command execution
1904           Dumps information about the progress of command execution.
1905
1906       bit 32 - destruction
1907           Dumps information about the destruction of Net::OpenSSH objects and
1908           the termination of the SSH master processes.
1909
1910       bit 64 - IO loop
1911           Dumps information about the progress of the IO loop on capture
1912           operations.
1913
1914       bit 128 - IO hexdumps
1915           Generates hexdumps of the information that travels through the SSH
1916           streams inside capture operations.
1917
1918       bit 512 - OS tracing of the master process
1919           Use the module Net::OpenSSH::OSTracer to trace the SSH master
1920           process at the OS level.
1921
1922       For instance, in order to activate all the debugging flags, you can
1923       use:
1924
1925         $Net::OpenSSH::debug = ~0;
1926
1927       Note that the meaning of the flags and the information generated is
1928       only intended for debugging of the module and may change without notice
1929       between releases.
1930
1931       If you are using password authentication, enabling debugging for
1932       IO::Tty may also show interesting information:
1933
1934           $IO::Tty::DEBUG = 1;
1935
1936       Finally, by default debugging output is sent to "STDERR". You can
1937       override it pointing $Net::OpenSSH::debug_fh to a different file
1938       handle. For instance:
1939
1940         BEGIN {
1941           open my $out, '>', '/tmp/debug.txt' or warn $!;
1942           $Net::OpenSSH::debug_fh = $out;
1943           $Net::OpenSSH::debug = -1;
1944         }
1945

SECURITY

1947       Q: Is this module secure?
1948
1949       A: Well, it tries to be!
1950
1951       From a security standpoint the aim of this module is to be as secure as
1952       OpenSSH, your operating system, your shell and in general your
1953       environment allow it to be.
1954
1955       It does not take any shortcut just to make your life easier if that
1956       means lowering the security level (for instance, disabling
1957       "StrictHostKeyChecking" by default).
1958
1959       In code supporting features that are not just proxied to OpenSSH, the
1960       module tries to keep the same standards of security as OpenSSH (for
1961       instance, checking directory and file permissions when placing the
1962       multiplexing socket).
1963
1964       On the other hand, and keeping with OpenSSH philosophy, the module lets
1965       you disable most (all?) of those security measures. But just because it
1966       lets you do it it doesn't mean it is a good idea to do so!!!
1967
1968       If you are a novice programmer or SSH user, and googling you have just
1969       found some flag that you don't understand but that seems to magically
1970       solve your connection problems... well, believe me, it is probably a
1971       bad idea to use it. Ask somebody how really knows first!
1972
1973       Just to make thinks clear, if your code contains any of the keywords
1974       from the (non-exclusive) list below and you don't know why, you are
1975       probably wrecking the security of the SSH protocol:
1976
1977         strict_mode
1978         StrictHostKeyChecking
1979         UserKnownHostsFile
1980
1981       Other considerations related to security you may like to know are as
1982       follows:
1983
1984       Taint mode
1985           The module supports working in taint mode.
1986
1987           If you are in an exposed environment, you should probably enable it
1988           for your script in order to catch any unchecked command for being
1989           executed in the remote side.
1990
1991       Web environments
1992           It is a bad idea to establish SSH connections from your webserver
1993           because if it becomes compromised in any way, the attacker would be
1994           able to use the credentials from your script to connect to the
1995           remote host and do anything he wishes there.
1996
1997       Command quoting
1998           The module can quote commands and arguments for you in a flexible
1999           and powerful way.
2000
2001           This is a feature you should use as it reduces the possibility of
2002           some attacker being able to inject and run arbitrary commands on
2003           the remote machine (and even for scripts that are not exposed it is
2004           always advisable to enable argument quoting).
2005
2006           Having said that, take into consideration that argument-quoting is
2007           just a hack to emulate the invoke-without-a-shell feature of Perl
2008           builtins such as "system" and alike. There may be bugs(*) on the
2009           quoting code, your particular shell may have different quoting
2010           rules with unhandled corner cases or whatever. If your script is
2011           exposed to the outside, you should check your inputs and restrict
2012           what you accept as valid.
2013
2014           [* even if this is one of the parts of the module more intensively
2015           tested!]
2016
2017       Shellshock
2018           (see Shellshock
2019           <http://en.wikipedia.org/wiki/Shellshock_%28software_bug%29>)
2020
2021           When executing local commands, the module always avoids calling the
2022           shell so in this way it is not affected by Shellshock.
2023
2024           Unfortunately, some commands ("scp", "rsync" and "ssh" when the
2025           "ProxyCommand" option is used) invoke other commands under the hood
2026           using the user shell. That opens the door to local Shellshock
2027           exploitation.
2028
2029           On the remote side invocation of the shell is unavoidable due to
2030           the protocol design.
2031
2032           By default, SSH does not forward environment variables but some
2033           Linux distributions explicitly change the default OpenSSH
2034           configuration to enable forwarding and acceptance of some specific
2035           ones (for instance "LANG" and "LC_*" on Debian and derivatives,
2036           Fedora does alike) and this also opens the door to Shellshock
2037           exploitation.
2038
2039           Note that the shell used to invoke commands is not "/bin/sh" but
2040           the user shell as configured in "/etc/passwd", PAM or whatever
2041           authentication subsystem is used by the local or remote operating
2042           system. Debian users, don't think you are not affected because your
2043           "/bin/sh" points to "dash"!
2044

FAQ

2046       Frequent questions about the module:
2047
2048       Connecting to switches, routers, etc.
2049           Q: I can not get the method "system", "capture", etc., to work when
2050           connecting to some router, switch, etc. What I am doing wrong?
2051
2052           A: Roughly, the SSH protocol allows for two modes of operation:
2053           command mode and interactive mode.
2054
2055           Command mode is designed to run single commands on the remote host.
2056           It opens a SSH channel between both hosts, asks the remote computer
2057           to run some given command and when it finishes, the channel is
2058           closed. It is what you get, for instance, when you run something
2059           as...
2060
2061             $ ssh my.unix.box cat foo.txt
2062
2063           ... and it is also the way Net::OpenSSH runs commands on the remote
2064           host.
2065
2066           Interactive mode launches a shell on the remote hosts with its
2067           stdio streams redirected to the local ones so that the user can
2068           transparently interact with it.
2069
2070           Some devices (as probably the one you are using) do not run an
2071           standard, general purpose shell (e.g. "bash", "csh" or "ksh") but
2072           some custom program specially targeted and limited to the task of
2073           configuring the device.
2074
2075           Usually, the SSH server running on these devices does not support
2076           command mode. It unconditionally attaches the restricted shell to
2077           any incoming SSH connection and waits for the user to enter
2078           commands through the redirected stdin stream.
2079
2080           The only way to work-around this limitation is to make your script
2081           talk to the restricted shell (1-open a new SSH session, 2-wait for
2082           the shell prompt, 3-send a command, 4-read the output until you get
2083           to the shell prompt again, repeat from 3). The best tool for this
2084           task is probably Expect, used alone or combined with Net::OpenSSH
2085           (see "Expect").
2086
2087           There are some devices that support command mode but that only
2088           accept one command per connection. In that cases, using Expect is
2089           also probably the best option.
2090
2091           Nowadays, there is a new player, Net::CLI::Interact that may be
2092           more suitable than Expect, and Net::Appliance::Session for working
2093           specifically with network devices.
2094
2095       Connection fails
2096           Q: I am unable to make the module connect to the remote host...
2097
2098           A: Have you read the troubleshooting section? (see
2099           "TROUBLESHOOTING").
2100
2101       Disable StrictHostKeyChecking
2102           Q: Why is "ssh" not run with "StrictHostKeyChecking=no"?
2103
2104           A: Using "StrictHostKeyChecking=no" relaxes the default security
2105           level of SSH and it will be relatively easy to end with a
2106           misconfigured SSH (for instance, when "known_hosts" is unwritable)
2107           that could be forged to connect to a bad host in order to perform
2108           man-in-the-middle attacks, etc.
2109
2110           I advice you to do not use that option unless you fully understand
2111           its implications from a security point of view.
2112
2113           If you want to use it anyway, past it to the constructor:
2114
2115             $ssh = Net::OpenSSH->new($host,
2116                      master_opts => [-o => "StrictHostKeyChecking=no"],
2117                      ...);
2118
2119       child process STDIN/STDOUT/STDERR is not a real system file handle
2120           Q: Calls to "system", "capture", etc. fail with the previous error,
2121           what's happening?
2122
2123           A: The reported stdio stream is closed or is not attached to a real
2124           file handle (e.g. it is a tied handle). Redirect it to "/dev/null"
2125           or to a real file:
2126
2127             my $out = $ssh->capture({stdin_discard => 1, stderr_to_stdout => 1},
2128                                     $cmd);
2129
2130           See also the mod_perl entry above.
2131
2132       Solaris (and AIX and probably others)
2133           Q: I was trying Net::OpenSSH on Solaris and seem to be running into
2134           an issue...
2135
2136           A: The SSH client bundled with Solaris is an early fork of OpenSSH
2137           that does not provide the multiplexing functionality required by
2138           Net::OpenSSH. You will have to install the OpenSSH client.
2139
2140           Precompiled packages are available from Sun Freeware
2141           (<http://www.sunfreeware.com>). There, select your OS version an
2142           CPU architecture, download the OpenSSH package and its dependencies
2143           and install them. Note that you do not need to configure Solaris to
2144           use the OpenSSH server "sshd".
2145
2146           Ensure that OpenSSH client is in your path before the system "ssh"
2147           or alternatively, you can hardcode the full path into your scripts
2148           as follows:
2149
2150             $ssh = Net::OpenSSH->new($host,
2151                                      ssh_cmd => '/usr/local/bin/ssh');
2152
2153           AIX and probably some other unixen, also bundle SSH clients lacking
2154           the multiplexing functionality and require installation of the real
2155           OpenSSH.
2156
2157       Can not change working directory
2158           Q: I want to run some command inside a given remote directory but I
2159           am unable to change the working directory. For instance:
2160
2161             $ssh->system('cd /home/foo/bin');
2162             $ssh->systen('ls');
2163
2164           does not list the contents of "/home/foo/bin".
2165
2166           What am I doing wrong?
2167
2168           A: Net::OpenSSH (and, for that matter, all the SSH modules
2169           available from CPAN but Net::SSH::Expect) run every command in a
2170           new session so most shell builtins that are run for its side
2171           effects become useless (e.g. "cd", "export", "ulimit", "umask",
2172           etc., usually, you can list them running "help" from the shell).
2173
2174           A work around is to combine several commands in one, for instance:
2175
2176             $ssh->system('cd /home/foo/bin && ls');
2177
2178           Note the use of the shell "&&" operator instead of ";" in order to
2179           abort the command as soon as any of the subcommands fail.
2180
2181           Also, several commands can be combined into one while still using
2182           the multi-argument quoting feature as follows:
2183
2184             $ssh->system(@cmd1, \\'&&', @cmd2, \\'&&', @cmd3, ...);
2185
2186       Running detached remote processes
2187           Q: I need to be able to ssh into several machines from my script,
2188           launch a process to run in the background there, and then return
2189           immediately while the remote programs keep running...
2190
2191           A: If the remote systems run some Unix/Linux variant, the right
2192           approach is to use nohup(1) that will disconnect the remote process
2193           from the stdio streams and to ask the shell to run the command on
2194           the background. For instance:
2195
2196             $ssh->system("nohup $long_running_command &");
2197
2198           Also, it may be possible to demonize the remote program. If it is
2199           written in Perl you can use App::Daemon for that (actually, there
2200           are several CPAN modules that provided that kind of functionality).
2201
2202           In any case, note that you should not use "spawn" for that.
2203
2204       MaxSessions server limit reached
2205           Q: I created an $ssh object and then fork a lot children processes
2206           which use this object. When the children number is bigger than
2207           "MaxSessions" as defined in sshd configuration (defaults to 10),
2208           trying to fork new remote commands will prompt the user for the
2209           password.
2210
2211           A: When the slave SSH client gets a response from the remote
2212           servers saying that the maximum number of sessions for the current
2213           connection has been reached, it fall backs to open a new direct
2214           connection without going through the multiplexing socket.
2215
2216           To stop that for happening, the following hack can be used:
2217
2218             $ssh = Net::OpenSSH->new(host,
2219                 default_ssh_opts => ['-oConnectionAttempts=0'],
2220                 ...);
2221
2222       Running remote commands with sudo
2223           Q: How can I run remote commands using "sudo" to become root first?
2224
2225           A: The simplest way is to tell "sudo" to read the password from
2226           stdin with the "-S" flag and to do not use cached credentials with
2227           the "-k" flag. You may also like to use the "-p" flag to tell
2228           "sudo" to print an empty prompt. For instance:
2229
2230             my @out = $ssh->capture({ stdin_data => "$sudo_passwd\n" },
2231                                     'sudo', '-Sk',
2232                                     '-p', '',
2233                                     '--',
2234                                     @cmd);
2235
2236           If the version of sudo installed on the remote host does not
2237           support the "-S" flag (it tells sudo to read the password from its
2238           STDIN stream), you can do it as follows:
2239
2240             my @out = $ssh->capture({ tty => 1,
2241                                       stdin_data => "$sudo_passwd\n" },
2242                                     'sudo', '-k',
2243                                     '-p', '',
2244                                     '--',
2245                                     @cmd);
2246
2247           This may generate an spurious and harmless warning from the SSH
2248           master connection (because we are requesting allocation of a tty on
2249           the remote side and locally we are attaching it to a regular pair
2250           of pipes).
2251
2252           If for whatever reason the methods described above fail, you can
2253           always revert to using Expect to talk to the remote "sudo". See the
2254           "examples/expect.pl" script from this module distribution.
2255

SEE ALSO

2257       OpenSSH client documentation ssh(1), ssh_config(5), the project web
2258       <http://www.openssh.org> and its FAQ
2259       <http://www.openbsd.org/openssh/faq.html>. scp(1) and rsync(1). The
2260       OpenSSH Wikibook <http://en.wikibooks.org/wiki/OpenSSH>.
2261
2262       Net::OpenSSH::Gateway for detailed instruction about how to get this
2263       module to connect to hosts through proxies and other SSH gateway
2264       servers.
2265
2266       Core perl documentation perlipc, "open" in perlfunc, "waitpid" in
2267       perlfunc.
2268
2269       IO::Pty to known how to use the pseudo tty objects returned by several
2270       methods on this package.
2271
2272       Net::SFTP::Foreign provides a compatible SFTP implementation.
2273
2274       Expect can be used to interact with commands run through this module on
2275       the remote machine (see also the "expect.pl" and <autosudo.pl> scripts
2276       in the examples directory).
2277
2278       SSH::OpenSSH::Parallel is an advanced scheduler that allows one to run
2279       commands in remote hosts in parallel. It is obviously based on
2280       Net::OpenSSH.
2281
2282       SSH::Batch allows one to run remote commands in parallel in a cluster.
2283       It is build on top on "Net::OpenSSH" also.
2284
2285       Other Perl SSH clients: Net::SSH::Perl, Net::SSH2, Net::SSH,
2286       Net::SSH::Expect, Net::SCP, Net::SSH::Mechanize.
2287
2288       Net::OpenSSH::Compat is a package offering a set of compatibility
2289       layers for other SSH modules on top of Net::OpenSSH.
2290
2291       IPC::PerlSSH, GRID::Machine allow execution of Perl code in remote
2292       machines through SSH.
2293
2294       SSH::RPC implements an RPC mechanism on top of SSH using Net::OpenSSH
2295       to handle the connections.
2296
2297       Net::CLI::Interact allows one to interact with remote shells and other
2298       services. It is specially suited for interaction with network
2299       equipment. The phrasebook approach it uses is very clever. You may also
2300       like to check the other modules <https://metacpan.org/author/OLIVER>
2301       from its author, Oliver Gorwits.
2302

BUGS AND SUPPORT

2304   Experimental features
2305       Support for the "restart" feature is experimental.
2306
2307       Object::Remote integration is highly experimental.
2308
2309       Support for tunnels targeting Unix sockets is highly experimental.
2310
2311       Support for the "setpgrp" feature is highly experimental.
2312
2313       Support for the gateway feature is highly experimental and mostly
2314       stalled.
2315
2316       Support for taint mode is experimental.
2317
2318   Known issues
2319       Net::OpenSSH does not work on Windows. OpenSSH multiplexing feature
2320       requires passing file handles through sockets, something that is not
2321       supported by any version of Windows.
2322
2323       It does not work on VMS either... well, probably, it does not work on
2324       anything not resembling a modern Linux/Unix OS.
2325
2326       Old versions of OpenSSH "ssh" may leave stdio streams in non-blocking
2327       mode. That can result on failures when writing to "STDOUT" or "STDERR"
2328       after using the module. In order to work-around this issue, Perl
2329       "fcntl" in perlfunc can be used to unset the non-blocking flag:
2330
2331         use Fcntl qw(F_GETFL F_SETFL O_NONBLOCK);
2332         my $flags = fcntl(STDOUT, F_GETFL, 0);
2333         fcntl(STDOUT, F_SETFL, $flags & ~O_NONBLOCK);
2334
2335   Reporting bugs and asking for help
2336       To report bugs send an email to the address that appear below or use
2337       the CPAN bug tracking system at <http://rt.cpan.org>.
2338
2339       Post questions related to how to use the module in PerlMonks
2340       <http://perlmonks.org/>, you will probably get faster responses than if
2341       you address me directly and I visit PerlMonks quite often, so I will
2342       see your question anyway.
2343
2344   Commercial support
2345       Commercial support, professional services and custom software
2346       development around this module are available through my current
2347       company. Drop me an email with a rough description of your requirements
2348       and we will get back to you ASAP.
2349
2350   My wishlist
2351       If you like this module and you are feeling generous, take a look at my
2352       Amazon Wish List: <http://amzn.com/w/1WU1P6IR5QZ42>.
2353
2354       Also consider contributing to the OpenSSH project this module builds
2355       upon: <http://www.openssh.org/donations.html>.
2356

TODO

2358       - Tests for "scp_*", "rsync_*" and "sftp" methods
2359
2360       - Make "pipe_in" and "pipe_out" methods "open_ex" based
2361
2362       - "auto_discard_streams" feature for mod_perl2 and similar environments
2363
2364       - Refactor open_ex support for multiple commands, maybe just keeping
2365         tunnel, ssh and raw
2366
2367       Send your feature requests, ideas or any feedback, please!
2368

CONTRIBUTING CODE

2370       The source code of this module is hosted at GitHub:
2371       <http://github.com/salva/p5-Net-OpenSSH>.
2372
2373       Code contributions to the module are welcome but you should obey the
2374       following rules:
2375
2376       Only Perl 5.8.4 required
2377           Yes, that's pretty old, but Net::OpenSSH is intended to be also
2378           used by system administrators that sometimes have to struggle with
2379           old systems. The reason to pick 5.8.4 is that it has been the
2380           default perl on Solaris for a long time.
2381
2382       Avoid the "All the world's a Linux PC" syndrome
2383           The module should work on any (barely) sane Unix or Linux operating
2384           system. Specially, it should not be assumed that the over-featured
2385           GNU utilities and toolchain are available.
2386
2387       Dependencies are optional
2388           In order to make the module very easy to install, no mandatory
2389           dependencies on other CPAN modules are allowed.
2390
2391           Optional modules, that are loaded only on demand, are acceptable
2392           when they are used for adding new functionality (as it is done, for
2393           instance, with IO::Pty).
2394
2395           Glue code for integration with 3rd party modules is also allowed
2396           (as it is done with Expect).
2397
2398           Usage of language extension modules and alike is not acceptable.
2399
2400       Tests should be lax
2401           We don't want false negatives when testing. In case of doubt tests
2402           should succeed.
2403
2404           Also, in case of tests invoking some external program, it should be
2405           checked that the external program is available and that it works as
2406           expected or otherwise skip those tests.
2407
2408       Backward compatibility
2409           Nowadays Net::OpenSSH is quite stable and there are lots of scripts
2410           out there using it that we don't want to break, so, keeping the API
2411           backward compatible is a top priority.
2412
2413           Probably only security issues could now justify a backward
2414           incompatible change.
2415
2416       Follow my coding style
2417           Look at the rest of the code.
2418
2419           I let Emacs do the formatting for me using cperl-mode PerlStyle.
2420
2421       Talk to me
2422           Before making a large change or implementing a new feature get in
2423           touch with me.
2424
2425           I may have my own ideas about how things should be done. It is
2426           better if you know them before hand, otherwise, you risk getting
2427           your patch rejected.
2428
2429       Well, actually you should know that I am quite good at rejecting
2430       patches but it is not my fault!
2431
2432       Most of the patches I get are broken in some way: they don't follow the
2433       main module principles, sometimes the author didn't get the full
2434       picture and solved the issue in a short-sighted way, etc.
2435
2436       In any case, you should not be discouraged to contribute. Even if your
2437       patch is not applied directly, seeing how it solves your requirements
2438       or, in the case of bugs, the underlying problem analysis may be very
2439       useful and help me to do it... my way.
2440
2441       I always welcome documentation corrections and improvements.
2442
2444       Copyright (C) 2008-2020 by Salvador FandiƱo (sfandino@yahoo.com)
2445
2446       This library is free software; you can redistribute it and/or modify it
2447       under the same terms as Perl itself, either Perl version 5.10.0 or, at
2448       your option, any later version of Perl 5 you may have available.
2449
2450
2451
2452perl v5.32.1                      2021-01-27                   Net::OpenSSH(3)
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