1REMCTL_OPEN(3) remctl Library Reference REMCTL_OPEN(3)
2
6 remctl_open - Connect to a remote remctl server
7
9 #include <remctl.h>
10 int remctl_open(struct remctl *r, const char *host,
12 unsigned short port,
13 const char *principal);
14 int remctl_open_addrinfo(struct remctl *r, const char *host,
16 const struct addrinfo *ai,
17 const char *principal);
18 int remctl_open_sockaddr(struct remctl *r, const char *host,
20 const struct sockaddr *addr, int addrlen,
21 const char *principal);
22 int remctl_open_fd(struct remctl *r, const char *host,
24 int fd, const char *principal);
25
27 remctl_open() opens a TCP connection to the given host on the given
28 port and then authenticates using the remctl protocol and the service
29 principal principal. r is a remctl struct created via remctl_new().
30 host must not be NULL. If port is 0, the library first attempts to
31 connect to the registered port of 4373 and then tries the legacy port
32 of 4444 if that fails. Future versions of the library will drop this
33 fallback to 4444. If principal is NULL, a service principal of
34 "host/host" is used, with the realm determined by domain-realm mapping.
35 remctl_open_addrinfo() operates in the same manner as remctl_open(),
37 but connects to the first usable address in ai, which must be a list of
38 results as returned by getaddrinfo(3). The host is used only to form
39 the default service principal, and may be NULL if principal is not
40 NULL.
41 remctl_open_sockaddr() is equivalent to remctl_open_addrinfo() with a
43 single addrinfo structure specifying the use of TCP with socket address
44 addr and length addrlen.
45 remctl_open_fd() operates in the same manner as remctl_open_addrinfo(),
47 but uses an already-established TCP connection identified by the file
48 descriptor fd. On Windows, fd is of type "SOCKET" and must be a valid
49 socket descriptor.
50 If no principal is specified and the default is used, the underlying
52 GSS-API library may canonicalize host via DNS before determining the
53 service principal, depending on your library configuration. Specifying
54 a principal disables this behavior.
55 The remctl protocol uses Kerberos via GSS-API for authentication. The
57 underlying GSS-API library will use the default ticket cache for
58 authentication, so to successfully use remctl_open(), the caller should
59 already have Kerberos tickets for an appropriate realm stored in its
60 default ticket cache. The environment variable KRB5CCNAME or the
61 remctl_set_ccache(3) function can be used to control which ticket cache
62 is used.
63 To control the timeout for the connect and for subsequent calls, see
65 the remctl_set_timeout(3) function. To control the source IP used by
66 remctl_open(), remctl_open_addrinfo(), and remctl_open_sockaddr(), see
67 the remctl_set_source_ip(3) function.
68
70 remctl_open() returns true on success and false on failure. On
71 failure, the caller should call remctl_error() to retrieve the error
72 message.
73
75 The remctl_open() interface has been provided by the remctl client
76 library since its initial release in version 2.0.
77 remctl_open_addrinfo(), remctl_open_sockaddr(), and remctl_open_fd()
78 were added in version 3.4.
79 The default port was changed to the IANA-registered port of 4373 in
81 version 2.11.
82 Support for IPv6 was added in version 2.4.
84
86 If the principal argument to remctl_open() is NULL, most GSS-API
87 libraries will canonicalize the host using DNS before deriving the
88 principal name from it. This means that when connecting to a remctl
89 server via a CNAME, remctl_open() will normally authenticate using a
90 principal based on the canonical name of the host instead of the
91 specified host parameter. This behavior may cause problems if two
92 consecutive DNS lookups of host may return two different results, such
93 as with some DNS-based load-balancing systems.
94 The canonicalization behavior is controlled by the GSS-API library;
96 with the MIT Kerberos GSS-API library, canonicalization can be disabled
97 by setting "rdns" to false in the [libdefaults] section of krb5.conf.
98 It can also be disabled by passing an explicit Kerberos principal name
99 via the principal argument, which will then be used without changes.
100 If canonicalization is desired, the caller may wish to canonicalize
101 host before calling remctl_open() to avoid problems with multiple DNS
102 calls returning different results.
103 The default behavior, when a port of 0 is given, of trying 4373 and
105 falling back to 4444 will be removed in a future version of this
106 library in favor of using the "remctl" service in /etc/services if set
107 and then falling back on only 4373. 4444 was the poorly-chosen
108 original remctl port and should be phased out.
109 Connections established using the alternate-open interfaces
111 remctl_open_fd(), remctl_open_addrinfo(), and remctl_open_sockaddr() do
112 not support the automatic connection-reopening which is used to give
113 the illusion of a single long-lived connection when sending multiple
114 commands to a server which supports only version 1 of the remctl
115 protocol. Therefore, when using these interfaces to open a connection
116 to such a server, it will only be possible to send a single command,
117 after which the connection must be closed and reopened before another
118 command can be sent.
119
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.
123
125 Russ Allbery <eagle@eyrie.org>
126
128 Copyright 2007-2009, 2014 The Board of Trustees of the Leland Stanford
129 Junior University
130 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 SPDX-License-Identifier: FSFAP
137
139 remctl_new(3), remctl_error(3), remctl_set_ccache(3),
140 remctl_set_source_ip(3), remctl_set_timeout(3)
141 The current version of the remctl library and complete details of the
143 remctl protocol are available from its web page at
144 <https://www.eyrie.org/~eagle/software/remctl/>.
1453.15 2018-05-05 REMCTL_OPEN(3)