Provided by: libnet-openssh-parallel-perl_0.12-1_all bug


       Net::OpenSSH::Parallel - Run SSH jobs in parallel


         use Net::OpenSSH::Parallel;

         my $pssh = Net::OpenSSH::Parallel->new();
         $pssh->add_host($_) for @hosts;

         $pssh->push('*', scp_put => '/local/file/path', '/remote/file/path');
         $pssh->push('*', command => 'gurummm',
                     '/remote/file/path', '/tmp/output');
         $pssh->push($special_host, command => 'prumprum', '/tmp/output');
         $pssh->push('*', scp_get => '/tmp/output', 'logs/%HOST%/output');



       Run this here, that there, etc.

       "Net::OpenSSH::Parallel" is an scheduler that can run commands in parallel in a set of
       hosts through SSH. It tries to find a compromise between being simple to use, efficient
       and covering a good part of the problem space of parallel process execution via SSH.

       Obviously, it is build on top of Net::OpenSSH!

       Common usage of the module is as follows:

       ·   create a "Net::OpenSSH::Parallel" object

       ·   register the hosts where you want to run commands with the "add_host" method

       ·   queue the actions you want to run (commands, file copy operations, etc.) using the
           "push" method.

       ·   call the "run" method and let the parallel scheduler take care of everything!

   Labelling hosts
       Every host is identified by an unique label that is given when the host is registered into
       the parallel scheduler. Usually, the host name is used also as the label, but this is not
       required by the module.

       The rationale behind using labels is that a hostname does not necessarily identify unique
       "remote processors" (for instance, sometimes your logical "remote processors" may be user
       accounts distributed over a set of hosts: "foo1@bar1", "foo2@bar1", "foo3@bar2", ...; a
       set of hosts that are accesible behind an unique IP, listening in different ports; etc.)

   Selecting hosts
       Several of the methods of this module (well, currently, just "push") accept a selector
       string to determine which of the registered hosts should be affected by the operation.

       For instance, in...

         $pssh->push('*', command => 'ls')

       the first argument is the selector. The one used here, "*", selects all the registered

       Other possible selectors are:

         'bar*'                # selects everything beginning by 'bar'
         'foo1,foo3,foo6'      # selects the hosts of the given names
         'bar*,foo1,foo3,foo6' # both
         '*doz*'               # everything containing 'doz'

       Note: I am still considering how the selector mini-language should be, don't hesitate to
       send your suggestions!

   Local resource usage
       When the number of hosts managed by the scheduler is too high, the local node can become

       Roughly, every SSH connection requires two local "ssh" processes (one to run the SSH
       connection and another one to launch the remote command) that results in around 5MB of RAM
       usage per host.

       CPU usage varies greatly depending on the tasks carried out. The most expensive are short
       remote tasks (because of the local process creation and destruction overhead) and tasks
       that transfer big ammounts of data through SSH (because of the encryption going on).

       In practice, CPU usage doesn't matter too much (mostly because the OS would be able to
       manage it but also because there is not too many things we can do to reduce it) and
       usually it is RAM about what we should be more concerned.

       The module accepts two parameters to limit resource usage:

       ·   "workers"

           is the maximun number of remote commands that can be running concurrently.

       ·   "connections"

           is the maximum number of SSH connections that can be active concurrently.

       In practice, limiting the maximum number of connections indirectly limits RAM usage and
       limiting the the maximum number of workers indirectly limits CPU usage.

       The module requires the maximum number of connections to be at least equal or bigger than
       the maximun number of workers, and it is recomended that "maximum_connections >= 2 *
       maximum_workers" (otherwise the scheduler will not be able to reuse connections

       You will have to experiment to find out which combinations give the best results in your
       particular scenarios.

       Also, for small sets of hosts you can just let these parameters unlimited.

   Variable expansion
       This module activates Net::OpenSSH variable expansion by default. That way, it is possible
       to easily customize the actions executed on every host in base to some of its properties.

       For instance:

         $pssh->push('*', scp_get => "/var/log/messages", "messages.%HOST%");

       copies the log files appending the name of the remote hosts to the local file names.

       The variables "HOST", "USER", "PORT" and "LABEL" are predefined.

   Error handling
       When something goes wrong (for instance, some host is unreachable, some connection dies,
       some command fails, etc.) the module can handle the error in several predefined ways as

       Error policies

       To set the error handling police, "new", "add_host" and "push" methods support and
       optional "on_error" argument that can take the following values (these constants are
       available from Net::OpenSSH::Parallel::Constants):

           Ignores the error and continues executing tasks in the host queue as it had never

           Aborts the processing on the corresponding host. The error will be propagated to other
           hosts joining it at any later point once the join is reached.

           In other words, this police aborts the queued jobs for this host and any other that
           has a dependency on it.

           Similar to "OSSH_ON_ERROR_ABORT" but will not propagate errors to other hosts via

           Causes all the host queues to be aborted as soon as possible (and that usually means
           after currently running actions end).

           The module will try to perform the current task again and again until it succeeds.
           This police can lead to an infinite loop and so its direct usage is discouraged (but
           see the following point about setting the policy dynamically).

       The default policy is "OSSH_ON_ERROR_ABORT".

       Setting the policy dynamically

       When a subroutine reference is used as the policy instead of the any of the constants
       previously described, the given subroutine will be called on error conditions as follows:

         $on_error->($pssh, $label, $error, $task)

       $pssh is a reference to the "Net::OpenSSH::Parallel" object, $label is the label
       associated to the host where the error happened. $error is the error type as defined in
       Net::OpenSSH::Parallel::Constants and $task is a reference to the task that was being
       carried out.

       The return value of the subroutine must be one of the described constants and the
       corresponding policy will be applied.

       Retrying connection errors

       If the module fails when trying to stablish a new SSH connection or when an existing
       connection dies unexpectedly, the option "reconnections" can be used to instruct the
       module to retry the connection until it succeds or the given maximun is reached.

       "reconnections" is accepted by both the "new" and "add_host" methods.


         $pssh->add_host('foo', reconnections => 3);

       Note that the reconnections maximum is not per host but per queued task.

       These are the available methods:

       $pssh = Net::OpenSSH::Parallel->new(%opts)
           creates a new object.

           The accepted options are:

           workers => $maximum_workers
               sets the maximum number of operations that can be carried out in parallel (see
               "Local resource usage").

           connections => $maximum_connections
               sets the maximum number of SSH connections that can be stablished simultaneously
               (see "Local resource usage").

               $maximum_connections must be equal or bigger than $maximum_workers

           reconnections => $maximum_reconnections
               when connecting to some host fails, this argument tells the module the maximum
               number of additional connection atemps that it should perform before giving up.
               The default value is zero.

               See also "Retrying connection errors".

           on_error => $policy
               Sets the error handling policy (see "Error handling").

       $pssh->add_host($label, %opts)
       $pssh->add_host($label, $host, %opts)
           registers a new host into the $pssh object.

           $label is the name used to refer to the registered host afterwards.

           When the hostname argument is ommited, the label is used also as the hostname.

           The accepted options are:

           on_error => $policy
               Sets the error handling policy (see "Error handling").

           reconnections => $maximum_reconnections
               See "Retrying connection errors".

           Any additional option will be passed verbatim to the Net::OpenSSH constructor later.
           For instance:

             $pssh->add_host($host, user => $user, password => $password);

       $pssh->push($selector, $action, \%opts, @action_args)
       $pssh->push($selector, $action, @action_args)
           pushes a new action into the queues selected by $selector.

           The supported actions are:

           command => @cmd
               queue the given shell command on the selected hosts.


                 $self->push('*', 'command'
                             { stdout_fh => $find_fh, stderr_to_stdout => 1 },
                             'find', '/my/dir');

           scp_get => @remote, $local
           scp_put => @local, $remote
               These methods queue an SCP remote file copy operation in the selected hosts.

           rsync_get => @remote, $local
           rsync_put => @local, $remote
               These methods queue an rsync remote file copy operation in the selected hosts.

           sub => sub { ... }, @extra_args
           sub { ... }, @extra_args
               Queues a call to a perl subroutine that will be executed locally.

               Note that subroutines are executed synchronously in the same process, so no other
               task will be scheduled while they are running.

               The sub is called as

                 $sub->($pssh, $label, @extra_args)

               where $pssh is the current Net::OpenSSH::Parallel object.

           parsub => sub { ... }, @extra_args
               Queues a call to a perl subroutine that will be executed locally on a forked

               The sub is called as

                 $sub->($label, $ssh, @extra_args)

               Where $ssh is an Net::OpenSSH object that can be used to interact with the remote

               Note that the interface is different to that of the "sub" action.

               An example of usage:

                 sub sudo_install {
                     my ($label, $ssh, @pkgs) = @_;
                     my ($pty) = $ssh->open2pty('sudo', 'apt-get', 'install', @pkgs);
                     my $expect = Expect->init($pty);
                     $expect->expect($timeout, ":");
                     $expect->expect($timeout, "\n");
                     while(<$expect>) { print };
                     close $expect;

                 $pssh->push('*', parsub => \&sudo_install, 'scummvm');

               If the subroutine dies or calls "_exit" with a non zero return code, the error
               handling code will be triggered (see "Error handling").

               The "parsub" action accepts the additional option "no_ssh" indicating that the
               $ssh object is not going to be used. For instance:

                 $pssh->push('*', parsub => { no_ssh => 1 },
                             sub {
                                   my $label = shift;
                                   { exec "gzip", "/tmp/file-$label" };
                                   die "exec failed: $!";

               That can make the script faster when the maximum number of simultaneous
               connections is limited. See "Local resource usage".

           join => $selector
               Joins allow to synchronize jobs between different servers.

               For instance:

                 $ssh->push('server_B', scp_get => '/tmp/foo', 'foo');
                 $ssh->push('server_A', join => 'server_B');
                 $ssh->push('server_A', scp_put => 'foo', '/tmp/foo');

               The join makes server_A to wait for the "scp_get" operation queued in server_B to
               finish before proceeding with the "scp_put".

               In general the join will make the selected servers wait for any task queued on the
               servers matched by $selector to finish before proceeding with the next queued

               One common usage is to synchronize all servers at some point:

                 $ssh->push('*', join => '*');

               By default, errors are propagated at joins. For instance, in the example above, if
               the scp_get operation queued on server_B failed, it would abort any further
               operation queued on server_B and any further operation queued after the join in
               server_A. See also "Error handling".

           here => $tag
               Push a tag in the stack that can be used as a target for goto operations.

           goto => $target
               Jumps forward until the given "here" tag is reached.

               Joins to other hosts queues will be ignored, and joins from other queues to this
               one will be succesfully fulfilled. For instance:

                 $pssh->add_host(A => ...);
                 $pssh->add_host(B => ...);
                 $pssh->push('*', cmd  => 'echo "hello from %HOST"');
                 $pssh->push('A', goto => 'there');
                 $pssh->push('A', join => 'B');                     # ignored by A on goto
                 $pssh->push('B', join => 'A');                     # fulfilled by A on goto
                 $pssh->push('*', cmd  => 'echo "hello from %HOST% again"');
                 $pssh->push('*', here => 'there');
                 $pssh->push('*', cmd  => 'echo "bye bye from %HOST%");

               Note that it is not possible to jump backguards.

               There is an special target "END" that can be used to jump to the end of the queue.

               Discards any additional operations queued. Any pending joins will be successfully

               It is equivalent to

                 $pssh->push('*', goto => 'END');

           When given, %opts can contain the following options:

           on_error => $fail_mode
           on_error => sub { ... }
               See "Error handling".

           or_goto => $tag
               Supported for "command", "scp_get", "scp_put", "rsync_get" and "rsync_put", when
               the command, scp or rsync operation fails a goto to the given target is performed.

               For instance:

                 $pssh->all(command => { or_goto => 'no_file' },
                                       "test -f /etc/foo");
                 $pssh->all(scp_get => "/etc/foo", "/tmp/foo-%LABEL%");
                 $pssh->all(here    => "no_file");

               Failures related to SSH errors do not trigger the goto but the error handling

           timeout => $seconds
               not implemented yet!

           on_done => sub { ... }
               not implemented yet!

           Any other option will be passed to the corresponding Net::OpenSSH method (spawn,
           scp_put, etc.).

       $pssh->all($action => @args)
       $pssh->all($action => \%opts, @args)
           Shortcut for...

             $pssh->push('*', $action, \%opts, @args);

           Runs the queued operations.

           It returns a true value on success and false otherwise.

           Returns the last error associated to the host of the given label.

           In list context returns a list of pairs "$label => $error" for the failed queues.

           In scalar context returns the number of failed queues.

FAQ - Frequently Asked Questions

       Running remote commands with sudo
           Q: I need to run the remote commands with sudo that asks for a password. How can I do

           A: First read the answer given to a similar question on Net::OpenSSH FAQ.

           The problem is that Net::OpenSSH::Parallel methods do not support the <stdin_data>
           option, so you will have to use an external file.

             $pssh->push('*', cmd => { stdin_file => $passwd_file },
                              'sudo', '-Skp', '', '--', @cmd);

           One trick you can use if you only have one password is to use the "DATA" file handle:

             $pssh->push('*', cmd => { stdin_fh => \*DATA},
                         'sudo', '-Skp', '', '--', @cmd);
             # and at the end of your script

           Or you can also use the "parsub" action:

             my %sudo_passwords = (host1 => "foo", ...);

             sub sudo {
               my ($label, $ssh, @cmd) = @_;
               $ssh->system({stdin_data => "$sudo_passwords{$label}\n"},
                            'sudo', '-Skp', '', '--', @cmd);

             $pssh->push('*', parsub => \&sudo, @cmd);


       ·   run N processes per host concurrently

           allow running more than one process per remote server concurrently

       ·   delay before reconnect

           when connecting fails, do not try to reconnect inmediately but after some predefined

       ·   rationalize debugging

           currently it is a mess

       ·   add loggin support

           log the operations performed in a given file

       ·   stdio redirection

           add support for better handling of the Net::OpenSSH stdio redirection facilities

       ·   configurable valid return codes

           Non zero exit code is not always an error.


       This module should be considered beta quality, everything seems to work but it may yet
       contain critical bugs.

       If you find any, report it via <> or by email (to,

       Feedback and comments are also welcome!

       The 'sub' and 'parsub' features should be considered experimental and its API or behaviour
       could be changed in future versions of the module.

   Reporting bugs
       In order to report a bug, write a minimal program that triggers it and place the following
       line at the beggining:

         $Net::OpenSSH::Parallel::debug = -1;

       Then, send me (via rt or email) the debugging output you get when you run it. Include also
       the source code of the script, a description of what is going wrong and the details of
       your OS and the versions of Perl, "Net::OpenSSH" and "Net::OpenSSH::Parallel" you are

   Development version
       The source code for this module is hosted at GitHub:

   Commercial support
       Commercial support, professional services and custom software development around this
       module are available through my current company. Drop me an email with a rough description
       of your requirements and we will get back to you ASAP.

   My wishlist
       If you like this module and you're feeling generous, take a look at my Amazon Wish List:

       Also consider contributing to the OpenSSH project this module builds upon:


       Net::OpenSSH is used to manage the SSH connections to the remote hosts.

       SSH::Batch has a similar focus as this module. In my opinion it is simpler to use but
       rather more limited.

       GRID::Machine allows to run perl code distributed in a cluster via SSH.

       If your application requires orchestating workflows more complex than those supported by
       Net::OpenSSH::Parallel, you should probably consider some POE or AnyEvent based solution
       (check POE::Component::OpenSSH).

       App::MrShell is another module allowing to run the same command in several host in

       Some people find easier to use Net::OpenSSH combined with Parallel::ForkManager, threads
       or Coro.

       Net::SSH::Mechanize is another framework written on top of AnyEvent that allows to run
       remote commands through SSH in parallel.


       Copyright X 2009-2012 by Salvador Fandin~o (

       This library is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself, either Perl version 5.10.0 or, at your option, any later version of
       Perl 5 you may have available.