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

Provided by: libnet-remctl-perl_3.18-1.1build2_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 2020, 2022 Russ Allbery <eagle@eyrie.org>

       Copyright 2007-2008, 2011-2014 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
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