Ubuntu Manpage: remctl, remctl_result_free - Simple remctl call to a remote server

Provided by: libremctl-dev_3.18-1.1build2_amd64

NAME

       remctl, remctl_result_free - Simple remctl call to a remote server

SYNOPSIS

       #include <remctl.h>

       struct remctl_result *
        remctl(const char *host, unsigned short port,
               const char *principal, const char **command);

       void remctl_result_free(struct remctl_result *result);

DESCRIPTION

remctl() provides a simplified client API for the remctl protocol. Given the host, port,
service principal for authentication, and command to run, it opens a connection to the
remote system, sends the command via the remctl protocol, reads the results, closes the
connection, and returns the result as a remctl_result struct.

host is a hostname or IP address and must be non-NULL. port is the port to connect to; if
0, the library first attempts to connect to the registered port of 4373 and then tries the
legacy port of 4444 if that fails. Future versions of the library will drop this fallback
to 4444. principal is the service principal to use for authentication; if NULL,
"host/host" is used, with the realm determined by domain-realm mapping. command is the
command to run as a NULL-terminated array of NUL-terminated strings.

If no principal is specified and the default is used, the underlying GSS-API library may
canonicalize host via DNS before determining the service principal, depending on your
library configuration. Specifying a principal disables this behavior.

The remctl protocol uses Kerberos via GSS-API for authentication. The underlying GSS-API
library will use the default ticket cache for authentication, so to successfully use
remctl(), the caller should already have Kerberos tickets for an appropriate realm stored
in its default ticket cache. The environment variable KRB5CCNAME can be used to control
which ticket cache is used. If the client needs to control which ticket cache is used
without changing the environment, use the full client API along with remctl_set_ccache(3).

remctl() returns a newly allocated remctl_result struct, which has the following members:

struct remctl_result {
char *error; /* remctl error if non-NULL. */
char *stdout_buf; /* Standard output. */
size_t stdout_len; /* Length of standard output. */
char *stderr_buf; /* Standard error. */
size_t stderr_len; /* Length of standard error. */
int status; /* Exit status of remote command. */
};

If error is non-NULL, a protocol error occurred and the command was not successfully
completed. Otherwise, standard output from the command will be stored in stdout_buf with
the length in stdout_len, standard error from the command will be stored in stderr_buf
with the length in stderr_len, and status will hold the exit status of the command.
Following the standard Unix convention, a 0 status should normally be considered success
and any non-zero status should normally be considered failure, although a given command
may have its own exit status conventions.

remctl_result_free() frees the remctl_result struct when the calling program is through
with it.

If you want more control over the steps of the protocol, issue multiple commands on the
same connection, control the ticket cache or source IP, set a timeout on replies, or send
data as part of the command that contains NULs, use the full API described in
remctl_new(3), remctl_open(3), remctl_commandv(3), and remctl_output(3).

RETURN VALUE

       remctl() returns NULL on failure to allocate a new remctl_result struct or on failure to
       allocate space to store an error message.  Otherwise, it returns a newly allocated
       remctl_result struct with either an error message in the error field or the results of the
       command filled out as described above.  If remctl() returns NULL, errno will be set to an
       appropriate error code (generally ENOMEM).

COMPATIBILITY

       This interface has been provided by the remctl client library since its initial release in
       version 2.0.

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

       Support for IPv6 was added in version 2.4.

CAVEATS

       If the principal argument to remctl() 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() 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() to avoid problems with multiple DNS calls returning different results.

       The default behavior, when a port of 0 is given, of trying 4373 and falling back to 4444
       will be removed in a future version of this library 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 2007-2009, 2014 The Board of Trustees of the Leland Stanford Junior University

       Copying and distribution of this file, with or without modification, are permitted in any
       medium without royalty provided the copyright notice and this notice are preserved.  This
       file is offered as-is, without any warranty.

       SPDX-License-Identifier: FSFAP