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

Provided by: libremctl-dev_3.13-1+deb9u1_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, 2008, 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.