Provided by: libnet-openssh-parallel-perl_0.14-1_all 
NAME
Net::OpenSSH::Parallel - Run SSH jobs in parallel
SYNOPSIS
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');
$pssh->run;
DESCRIPTION
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!
Labeling 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 accessible
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 hosts.
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, do not 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 overloaded.
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 amounts of
data through SSH (because of the encryption going on).
In practice, CPU usage does not 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 maximum 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 maximum
number of workers, and it is recommended that "maximum_connections >= 2 * maximum_workers" (otherwise the
scheduler will not be able to reuse connections efficiently).
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 follows:
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):
OSSH_ON_ERROR_IGNORE
Ignores the error and continues executing tasks in the host queue as it had never happened.
OSSH_ON_ERROR_ABORT
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.
OSSH_ON_ERROR_DONE
Similar to "OSSH_ON_ERROR_ABORT" but will not propagate errors to other hosts via joins.
OSSH_ON_ERROR_ABORT_ALL
Causes all the host queues to be aborted as soon as possible (and that usually means after currently
running actions end).
OSSH_ON_ERROR_REPEAT
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 establish 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 succeeds or the given maximum is reached.
"reconnections" is accepted by both the "new" and "add_host" methods.
Example:
$pssh->add_host('foo', reconnections => 3);
Note that the reconnections maximum is not per host but per queued task.
API
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 established 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 attempts 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 omitted, 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.
Example:
$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 a "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 process.
The sub is called as
$sub->($label, $ssh, @extra_args)
Where $ssh is an Net::OpenSSH object that can be used to interact with the remote machine.
Note that the interface is different to that of the "sub" action.
An example of usage:
sub sudo_install {
my ($label, $ssh, @pkgs) = @_;
my ($pty) = $ssh->open2pty('sudo', 'apt-get', 'install', @pkgs);
my $expect = Expect->init($pty);
$expect->raw_pty(1);
$expect->expect($timeout, ":");
$expect->send("$passwd\n");
$expect->expect($timeout, "\n");
$expect->raw_pty(0);
while(<$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 tasks.
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
successfully 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 backwards.
There is an special target "END" that can be used to jump to the end of the queue.
stop
Discards any additional operations queued. Any pending joins will be successfully fulfilled.
It is equivalent to
$pssh->push('*', goto => 'END');
connect
Just ensures that connecting to the remote machine is possible without doing any other action.
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 code.
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);
$pssh->run
Runs the queued operations.
It returns a true value on success and false otherwise.
$pssh->get_error($label)
Returns the last error associated to the host of the given label.
$pssh->get_errors
In list context returns a list of pairs "$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 it?
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:
$pssh->push('*', cmd => { stdin_fh => \*DATA},
'sudo', '-Skp', '', '--', @cmd);
...
# and at the end of your script
__DATA__
this-is-my-remote-password-for-sudo
Or you can also use the "parsub" action:
my %sudo_passwords = (host1 => "foo", ...);
sub sudo {
my ($label, $ssh, @cmd) = @_;
$ssh->system({stdin_data => "$sudo_passwords{$label}\n"},
'sudo', '-Skp', '', '--', @cmd);
}
$pssh->push('*', parsub => \&sudo, @cmd);
TODO
• 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 immediately but after some predefined period
• rationalize debugging
currently it is a mess
• add logging 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.
BUGS AND SUPPORT
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 <http://rt.cpan.org> or by email (to sfandino@yahoo.com), please.
Feedback and comments are also welcome!
The 'sub' and 'parsub' features should be considered experimental and its API or behavior 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
beginning:
$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 using.
Development version
The source code for this module is hosted at GitHub: <http://github.com/salva/p5-Net-OpenSSH-Parallel>.
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 are feeling generous, take a look at my Amazon Wish List:
<http://amzn.com/w/1WU1P6IR5QZ42>
Also consider contributing to the OpenSSH project this module builds upon:
<http://www.openssh.org/donations.html>.
SEE ALSO
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 orchestrating work-flows 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 parallel.
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 AND LICENSE
Copyright © 2009-2012, 2015 by Salvador Fandiño (sfandino@yahoo.com).
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.
perl v5.40.1 2025-09-06 Net::OpenSSH::Parallel(3pm)