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36 .\" @(#)rcmd.3 8.1 (Berkeley) 6/4/93
38 .\" Contributed as Linux man page by David A. Holland, 970908
39 .\" I have not checked whether the Linux situation is exactly the same.
41 .\" 2007-12-08, mtk, Converted from mdoc to man macros
43 .TH RCMD 3 2017-09-15 "Linux" "Linux Programmer's Manual"
45 rcmd, rresvport, iruserok, ruserok, rcmd_af,
46 rresvport_af, iruserok_af, ruserok_af \- routines for returning a
47 stream to a remote command
50 .B #include <netdb.h> \ \ \fP/* Or <unistd.h> on some systems */
52 .BI "int rcmd(char **" ahost ", unsigned short " inport ", const char *" locuser ", "
53 .BI " const char *" remuser ", const char *" cmd ", int *" fd2p );
55 .BI "int rresvport(int *" port );
57 .BI "int iruserok(uint32_t " raddr ", int " superuser ", "
58 .BI " const char *" ruser ", const char *" luser );
60 .BI "int ruserok(const char *" rhost ", int " superuser ", "
61 .BI " const char *" ruser ", const char *" luser );
63 .BI "int rcmd_af(char **" ahost ", unsigned short " inport ", const char *" locuser ", "
64 .BI " const char *" remuser ", const char *" cmd ", int *" fd2p ,
65 .BI " sa_family_t " af );
67 .BI "int rresvport_af(int *" port ", sa_family_t " af );
69 .BI "int iruserok_af(const void *" raddr ", int " superuser ", "
70 .BI " const char *" ruser ", const char *" luser \
71 ", sa_family_t " af );
73 .BI "int ruserok_af(const char *" rhost ", int " superuser ", "
74 .BI " const char *" ruser ", const char *" luser \
75 ", sa_family_t " af );
79 Feature Test Macro Requirements for glibc (see
80 .BR feature_test_macros (7)):
93 Glibc 2.19 and earlier:
98 function is used by the superuser to execute a command on
99 a remote machine using an authentication scheme based
100 on privileged port numbers.
104 returns a file descriptor to a socket
105 with an address in the privileged port space.
110 functions are used by servers
111 to authenticate clients requesting service with
113 All four functions are used by the
115 server (among others).
124 .BR gethostbyname (3),
125 returning \-1 if the host does not exist.
128 is set to the standard name of the host
129 and a connection is established to a server
130 residing at the well-known Internet port
133 If the connection succeeds,
134 a socket in the Internet domain of type
136 is returned to the caller, and given to the remote
143 is nonzero, then an auxiliary channel to a control
144 process will be set up, and a file descriptor for it will be placed
147 The control process will return diagnostic
148 output from the command (unit 2) on this channel, and will also
149 accept bytes on this channel as being UNIX signal numbers, to be
150 forwarded to the process group of the command.
155 (unit 2 of the remote
156 command) will be made the same as the
159 provision is made for sending arbitrary signals to the remote process,
160 although you may be able to get its attention by using out-of-band data.
162 The protocol is described in detail in
168 function is used to obtain a socket with a privileged
170 This socket is suitable for use by
172 and several other functions.
173 Privileged ports are those in the range 0 to 1023.
174 Only a privileged process
175 (on Linux: a process that has the
176 .B CAP_NET_BIND_SERVICE
177 capability in the user namespace governing its network namespace).
178 is allowed to bind to a privileged port.
179 In the glibc implementation,
180 this function restricts its search to the ports from 512 to 1023.
183 argument is value-result:
184 the value it supplies to the call is used as the starting point
185 for a circular search of the port range;
186 on (successful) return, it contains the port number that was bound to.
188 .SS iruserok() and ruserok()
194 functions take a remote host's IP address or name, respectively,
195 two usernames and a flag indicating whether the local user's
196 name is that of the superuser.
199 the superuser, it checks the
202 If that lookup is not done, or is unsuccessful, the
204 in the local user's home directory is checked to see if the request for
207 If this file does not exist, is not a regular file, is owned by anyone
208 other than the user or the superuser, is writable by anyone other
209 than the owner, or is hardlinked anywhere, the check automatically fails.
210 Zero is returned if the machine name is listed in the
212 file, or the host and remote username are found in the
219 If the local domain (as obtained from
221 is the same as the remote domain, only the machine name need be specified.
223 If the IP address of the remote host is known,
225 should be used in preference to
227 as it does not require trusting the DNS server for the remote host's domain.
229 All of the functions described above work with IPv4
232 The "_af" variants take an extra argument that allows the
233 socket address family to be specified.
234 For these functions, the
236 argument can be specified as
248 returns a valid socket descriptor on success.
249 It returns \-1 on error and prints a diagnostic message on the standard error.
254 returns a valid, bound socket descriptor on success.
255 It returns \-1 on error with the global value
257 set according to the reason for failure.
260 is overloaded to mean "All network ports in use."
262 For information on the return from
274 functions are provide in glibc since version 2.2.
276 For an explanation of the terms used in this section, see
282 Interface Attribute Value
286 T} Thread safety MT-Unsafe
290 T} Thread safety MT-Safe
297 T} Thread safety MT-Safe locale
302 Present on the BSDs, Solaris, and many other systems.
304 functions appeared in
306 The "_af" variants are more recent additions,
307 and are not present on as wide a range of systems.
312 are declared in glibc headers only since version 2.12.
313 .\" Bug filed 25 Nov 2007:
314 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=5399