remctl_result_free(3)

1REMCTL(3)                  remctl Library Reference                  REMCTL(3)
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NAME

6       remctl, remctl_result_free - Simple remctl call to a remote server
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SYNOPSIS

9       #include <remctl.h>
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11       struct remctl_result *
12        remctl(const char *host, unsigned short port,
13               const char *principal, const char **command);
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15       void remctl_result_free(struct remctl_result *result);
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DESCRIPTION

18       remctl() provides a simplified client API for the remctl protocol.
19       Given the host, port, service principal for authentication, and command
20       to run, it opens a connection to the remote system, sends the command
21       via the remctl protocol, reads the results, closes the connection, and
22       returns the result as a remctl_result struct.
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24       host is a hostname or IP address and must be non-NULL.  port is the
25       port to connect to; if 0, the library first attempts to connect to the
26       registered port of 4373 and then tries the legacy port of 4444 if that
27       fails.  Future versions of the library will drop this fallback to 4444.
28       principal is the service principal to use for authentication; if NULL,
29       "host/host" is used, with the realm determined by domain-realm mapping.
30       command is the command to run as a NULL-terminated array of NUL-
31       terminated strings.
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33       If no principal is specified and the default is used, the underlying
34       GSS-API library may canonicalize host via DNS before determining the
35       service principal, depending on your library configuration.  Specifying
36       a principal disables this behavior.
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38       The remctl protocol uses Kerberos via GSS-API for authentication.  The
39       underlying GSS-API library will use the default ticket cache for
40       authentication, so to successfully use remctl(), the caller should
41       already have Kerberos tickets for an appropriate realm stored in its
42       default ticket cache.  The environment variable KRB5CCNAME can be used
43       to control which ticket cache is used.  If the client needs to control
44       which ticket cache is used without changing the environment, use the
45       full client API along with remctl_set_ccache(3).
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47       remctl() returns a newly allocated remctl_result struct, which has the
48       following members:
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50           struct remctl_result {
51               char *error;                /* remctl error if non-NULL. */
52               char *stdout_buf;           /* Standard output. */
53               size_t stdout_len;          /* Length of standard output. */
54               char *stderr_buf;           /* Standard error. */
55               size_t stderr_len;          /* Length of standard error. */
56               int status;                 /* Exit status of remote command. */
57           };
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59       If error is non-NULL, a protocol error occurred and the command was not
60       successfully completed.  Otherwise, standard output from the command
61       will be stored in stdout_buf with the length in stdout_len, standard
62       error from the command will be stored in stderr_buf with the length in
63       stderr_len, and status will hold the exit status of the command.
64       Following the standard Unix convention, a 0 status should normally be
65       considered success and any non-zero status should normally be
66       considered failure, although a given command may have its own exit
67       status conventions.
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69       remctl_result_free() frees the remctl_result struct when the calling
70       program is through with it.
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72       If you want more control over the steps of the protocol, issue multiple
73       commands on the same connection, control the ticket cache or source IP,
74       set a timeout on replies, or send data as part of the command that
75       contains NULs, use the full API described in remctl_new(3),
76       remctl_open(3), remctl_commandv(3), and remctl_output(3).
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RETURN VALUE

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

87       This interface has been provided by the remctl client library since its
88       initial release in version 2.0.
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90       The default port was changed to the IANA-registered port of 4373 in
91       version 2.11.
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93       Support for IPv6 was added in version 2.4.
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CAVEATS

96       If the principal argument to remctl() is NULL, most GSS-API libraries
97       will canonicalize the host using DNS before deriving the principal name
98       from it.  This means that when connecting to a remctl server via a
99       CNAME, remctl() will normally authenticate using a principal based on
100       the canonical name of the host instead of the specified host parameter.
101       This behavior may cause problems if two consecutive DNS lookups of host
102       may return two different results, such as with some DNS-based load-
103       balancing systems.
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105       The canonicalization behavior is controlled by the GSS-API library;
106       with the MIT Kerberos GSS-API library, canonicalization can be disabled
107       by setting "rdns" to false in the [libdefaults] section of krb5.conf.
108       It can also be disabled by passing an explicit Kerberos principal name
109       via the principal argument, which will then be used without changes.
110       If canonicalization is desired, the caller may wish to canonicalize
111       host before calling remctl() to avoid problems with multiple DNS calls
112       returning different results.
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114       The default behavior, when a port of 0 is given, of trying 4373 and
115       falling back to 4444 will be removed in a future version of this
116       library in favor of using the "remctl" service in /etc/services if set
117       and then falling back on only 4373.  4444 was the poorly-chosen
118       original remctl port and should be phased out.
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NOTES

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

125       Russ Allbery <eagle@eyrie.org>
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COPYRIGHT AND LICENSE

128       Copyright 2007, 2008, 2009, 2014 The Board of Trustees of the Leland
129       Stanford Junior University
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131       Copying and distribution of this file, with or without modification,
132       are permitted in any medium without royalty provided the copyright
133       notice and this notice are preserved.  This file is offered as-is,
134       without any warranty.
135