Ubuntu Manpage: Net::Remctl - Perl bindings for remctl (Kerberos remote command execution)

Provided by: libnet-remctl-perl_3.10-1ubuntu1_amd64

NAME

       Net::Remctl - Perl bindings for remctl (Kerberos remote command execution)

SYNOPSIS

           # Simplified form.
           use Net::Remctl;
           my $result = remctl("hostname", undef, undef, "test", "echo", "Hi");
           if ($result->error) {
               die "test echo failed with error ", $result->error, "\n";
           } else {
               warn $result->stderr;
               print $result->stdout;
               exit $result->status;
           }

           # Full interface.
           use Net::Remctl ();
           my $remctl = Net::Remctl->new;
           $remctl->open("hostname")
               or die "Cannot connect to hostname: ", $remctl->error, "\n";
           $remctl->command("test", "echo", "Hi there")
               or die "Cannot send command: ", $remctl->error, "\n";
           my $output;
           do {
               $output = $remctl->output;
               if ($output->type eq 'output') {
                   if ($output->stream == 1) {
                       print $output->data;
                   } elsif ($output->stream == 2) {
                       warn $output->data;
                   }
               } elsif ($output->type eq 'error') {
                   warn $output->error, "\n";
               } elsif ($output->type eq 'status') {
                   exit $output->status;
               } else {
                   die "Unknown output token from library: ", $output->type, "\n";
               }
           } while ($output->type eq 'output');
           $remctl->noop or die "Cannot send NOOP: ", $remctl->error, "\n";

DESCRIPTION

Net::Remctl provides Perl bindings to the libremctl client library. remctl is a protocol
for remote command execution using GSS-API authentication. The specific allowable
commands must be listed in a configuration file on the remote system and the remote system
can map the remctl command names to any local command without exposing that mapping to the
client. This module implements a remctl client.

Simplified Interface
If you want to run a single command on a remote system and get back the output and exit
status, you can use the exported remctl() function:

remctl(HOSTNAME, PORT, PRINCIPAL, COMMAND, [ARGS, ...])
Runs a command on the remote system and returns a Net::Remctl::Result object (see
below). HOSTNAME is the remote host to contact. PORT is the port of the remote
remctld server and may be 0 to tell the library to use the default (first try 4373,
the registered remctl port, and fall back to the legacy 4444 port if that fails).
PRINCIPAL is the principal of the server to use for authentication; pass in the empty
string to use the default of host/HOSTNAME, with the realm determined by domain-realm
mapping. The remaining arguments are the remctl command and arguments passed to the
remote server.

As far as the module is concerned, undef may be passed as PORT and PRINCIPAL and is
the same as 0 and the empty string respectively. However, Perl will warn about
passing undef explicitly as a function argument.

The return value is a Net::Remctl::Result object which supports the following methods:

error()
Returns the error message from either the remote host or from the local client
library (if, for instance, contacting the remote host failed). Returns undef if
there was no error. Checking whether error() returns undef is the supported way
of determining whether the remctl() call succeeded.

stdout()
Returns the command's standard output or undef if there was none.

stderr()
Returns the command's standard error or undef if there was none.

status()
Returns the command's exit status.

Each call to remctl() will open a new connection to the remote host and close it after
retrieving the results of the command. To maintain a persistent connection, use the
full interface described below.

Full Interface
The full remctl library interface requires that the user do more bookkeeping, but it
provides more flexibility and allows one to issue multiple commands on the same persistent
connection (provided that the remote server supports protocol version two; if not, the
library will transparently fall back to opening a new connection for each command).

To use the full interface, first create a Net::Remctl object with new() and then connect()
to a remote server. Then, issue a command() and call output() to retrieve output tokens
(as Net::Remctl::Output objects) until a status token is received. Destroying the
Net::Remctl object will close the connection.

Methods below are annotated with the version at which they were added. Note that this is
the version of the remctl distribution, which only matches the Net::Remctl module version
in 3.05 and later. Earlier versions of the module used an independent versioning system
that is not documented here, and versions earlier than 3.05 are therefore not suitable for
use with "use".

The supported object methods are:

new()
[2.8] Create a new Net::Remctl object. This doesn't attempt to connect to a host and
hence will only fail (by throwing an exception) if the library cannot allocate memory.

error()
[2.8] Retrieves the error message from the last failing operation and returns it as a
string.

set_ccache(CCACHE)
[3.00] Sets the GSS-API credential cache for outgoing connections to CCACHE, which is
normally the path to a Kerberos ticket cache but may have other valid forms depending
on the underlying Kerberos implementation in use by GSS-API. This method will affect
all subsequent open() calls on at least the same object, but will have no effect on
connections that are already open. Returns true on success and false on failure.

If the remctl client library was built against a Kerberos library and the GSS-API
library supported gss_krb5_import_cred, this call affects only this Net::Remctl
object. Otherwise, this will affect not only all subsequent open() calls for the same
object, but all subsequent remctl connections of any kind from the same process, and
even other GSS-API connections from the same process unrelated to remctl.

Not all GSS-API implementations support setting the credential cache. If this is not
supported, false will be returned.

set_source_ip(SOURCE)
[3.00] Sets the source IP for outgoing connections to SOURCE, which can be either an
IPv4 or an IPv6 address (if IPv6 is supported). It must be an IP address, not a host
name. This will affect all subsequent open() calls on the same object, but will have
no effect on connections that are already open. Returns true on success and false on
failure.

set_timeout(TIMEOUT)
[3.01] Sets the timeout for connections and commands to TIMEOUT, which should be an
integer number of seconds. TIMEOUT may be 0 to clear a timeout that was previously
set. All subsequent operations on this Net::Remctl object will be subject to this
timeout, including open() if called prior to calling open(). Returns true on success
and false on failure. Failure is only possible if TIMEOUT is malformed.

The timeout is a timeout on network activity from the server, not on a complete
operation. So, for example, a timeout of ten seconds just requires that the server
send some data every ten seconds. If the server sends only tiny amounts of data at a
time, the complete operation could take much longer than ten seconds without
triggering the timeout.

open(HOSTNAME[, PORT[, PRINCIPAL]])
[2.8] Connect to HOSTNAME on port PORT using PRINCIPAL as the remote server's
principal for authentication. If PORT is omitted or 0, use the default (first try
4373, the registered remctl port, and fall back to the legacy 4444 port if that
fails). If PRINCIPAL is omitted or the empty string, use the default of
host/HOSTNAME, with the realm determined by domain-realm mapping. Returns true on
success, false on failure. On failure, call error() to get the failure message.

command(COMMAND[, ARGS, ...])
[2.8] Send the command and arguments to the remote host. The command and the
arguments may, under the remctl protocol, contain any character, but be aware that
most remctl servers will reject commands or arguments containing ASCII 0 (NUL), so
currently this cannot be used for upload of arbitrary unencoded binary data. Returns
true on success (meaning success in sending the command, and implying nothing about
the result of the command), false on failure. On failure, call error() to get the
failure message.

output()
[2.8] Returns the next output token from the remote host. The token is returned as a
Net::Remctl::Output object, which supports the following methods:

type()
Returns the type of the output token, which will be one of "output", "error",
"status", or "done". A command will result in either one "error" token or zero or
more "output" tokens followed by a "status" token. After either a "error" or
"status" token is seen, another command can be issued. If the caller tries to
retrieve another output token when it has already consumed all of them for that
command, the library will return a "done" token.

data()
Returns the contents of the token. This method only makes sense for "output" and
"error" tokens; otherwise, it will return undef. Note that the returned value may
contain any character, including ASCII 0 (NUL).

length()
Returns the length of the data in the token. As with data(), this method only
makes sense for the "output" and "error" tokens. It will return 0 if there is no
data or if the data is zero-length.

stream()
For an "output" token, returns the stream with which the data is associated.
Currently, only two stream values will be used: 1, meaning standard output; and 2,
meaning standard error. The value is undefined for all other output token types.

status()
For a "status" token, returns the exit status of the remote command. The value is
undefined for all other token types.

error()
For an "error" token, returns the remctl error code for the protocol error. The
text message will be returned by data(). The value is undefined for all other
token types.

noop()
[3.00] Send a NOOP message to the server and read the reply. This is primarily used
to keep a connection to a remctl server alive, such as through a firewall with a
session timeout, while waiting to issue further commands. Returns true on success,
false on failure. On failure, call error() to get the failure message.

The NOOP message requires protocol version 3 support in the server, so the caller
should be prepared for this function to fail, indicating that the connection could not
be kept alive and possibly that it was closed by the server. In this case, the client
will need to explicitly reopen the connection with open().

Note that, due to internal implementation details in the library, the Net::Remctl::Output
object returned by output() will be invalidated by the next call to command() or output()
or by destroying the producing Net::Remctl object. Therefore, any data in the output
token should be processed and stored if needed before making any further Net::Remctl
method calls on the same object.

COMPATIBILITY

       The main object methods are annotated above with the version in which that interface was
       added.  All unannotated methods have been present since the first release of the module.

       Support for the gss_krb5_import_cred method of isolating the changed ticket cache to only
       this remctl client object was added in version 3.5.

       The default port was changed to the IANA-registered port of 4373 in version 2.11.

       This module was first released with version 2.8.

CAVEATS

If the principal argument to remctl() or remctl_open() is NULL, most GSS-API libraries
will canonicalize the host using DNS before deriving the principal name from it. This
means that when connecting to a remctl server via a CNAME, remctl() and remctl_open() will
normally authenticate using a principal based on the canonical name of the host instead of
the specified host parameter. This behavior may cause problems if two consecutive DNS
lookups of host may return two different results, such as with some DNS-based load-
balancing systems.

The canonicalization behavior is controlled by the GSS-API library; with the MIT Kerberos
GSS-API library, canonicalization can be disabled by setting "rdns" to false in the
[libdefaults] section of krb5.conf. It can also be disabled by passing an explicit
Kerberos principal name via the principal argument, which will then be used without
changes. If canonicalization is desired, the caller may wish to canonicalize host before
calling remctl() or remctl_open() to avoid problems with multiple DNS calls returning
different results.

The default behavior, when the port is not specified, of trying 4373 and falling back to
4444 will be removed in a future version of this module in favor of using the "remctl"
service in /etc/services if set and then falling back on only 4373. 4444 was the poorly-
chosen original remctl port and should be phased out.

NOTES

       The remctl port number, 4373, was derived by tracing the diagonals of a QWERTY keyboard up
       from the letters "remc" to the number row.

AUTHOR

       Russ Allbery <eagle@eyrie.org>

COPYRIGHT AND LICENSE

       Copyright 2007, 2008, 2011, 2012, 2013, 2014 The Board of Trustees of the Leland Stanford
       Junior University

       Permission is hereby granted, free of charge, to any person obtaining a copy of this
       software and associated documentation files (the "Software"), to deal in the Software
       without restriction, including without limitation the rights to use, copy, modify, merge,
       publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
       to whom the Software is furnished to do so, subject to the following conditions:

       The above copyright notice and this permission notice shall be included in all copies or
       substantial portions of the Software.

       THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
       INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
       PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
       FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
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