1RCMD(3)                    Linux Programmer's Manual                   RCMD(3)
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NAME

6       rcmd, rresvport, iruserok, ruserok, rcmd_af, rresvport_af, iruserok_af,
7       ruserok_af - routines for returning a stream to a remote command
8

SYNOPSIS

10       #include <netdb.h>   /* Or <unistd.h> on some systems */
11
12       int rcmd(char **ahost, int inport, const char *locuser,
13                const char *remuser, const char *cmd, int *fd2p);
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15       int rresvport(int *port);
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17       int iruserok(uint32_t raddr, int superuser,
18                    const char *ruser, const char *luser);
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20       int ruserok(const char *rhost, int superuser,
21                   const char *ruser, const char *luser);
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23       int rcmd_af(char **ahost, int inport, const char *locuser,
24                   const char *remuser, const char *cmd, int *fd2p,
25                   sa_family_t af);
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27       int rresvport_af(int *port, sa_family_t af);
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29       int iruserok_af(uint32_t raddr, int superuser,
30                       const char *ruser, const char *luser, sa_family_t af);
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32       int ruserok_af(const char *rhost, int superuser,
33                      const char *ruser, const char *luser, sa_family_t af);
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35   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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37       rcmd(),    rcmd_af(),    rresvport(),    rresvport_af(),    iruserok(),
38       iruserok_af(), ruserok(), ruserok_af(): _BSD_SOURCE
39

DESCRIPTION

41       The  rcmd() function is used by the superuser to execute a command on a
42       remote machine using an authentication scheme based on privileged  port
43       numbers.   The  rresvport()  function  returns a descriptor to a socket
44       with an address in the  privileged  port  space.   The  iruserok()  and
45       ruserok()  functions  are  used  by  servers  to  authenticate  clients
46       requesting service with rcmd().  All four functions  are  used  by  the
47       rshd(8) server (among others).
48
49   rcmd()
50       The  rcmd()  function  looks up the host *ahost using gethostbyname(3),
51       returning -1 if the host does not exist.  Otherwise *ahost  is  set  to
52       the  standard  name  of  the  host and a connection is established to a
53       server residing at the well-known Internet port inport.
54
55       If the connection succeeds, a socket in the  Internet  domain  of  type
56       SOCK_STREAM  is returned to the caller, and given to the remote command
57       as stdin and stdout.  If fd2p is nonzero, then an auxiliary channel  to
58       a  control  process  will  be  set  up, and a descriptor for it will be
59       placed in *fd2p.  The control process  will  return  diagnostic  output
60       from  the  command (unit 2) on this channel, and will also accept bytes
61       on this channel as being UNIX signal numbers, to be  forwarded  to  the
62       process group of the command.  If fd2p is 0, then the stderr (unit 2 of
63       the remote command) will be made the same as the stdout and  no  provi‐
64       sion  is  made  for  sending  arbitrary  signals to the remote process,
65       although you may be able to get  its  attention  by  using  out-of-band
66       data.
67
68       The protocol is described in detail in rshd(8).
69
70   rresvport()
71       The  rresvport()  function is used to obtain a socket with a privileged
72       port bound to it.  This socket is suitable for use by rcmd()  and  sev‐
73       eral  other  functions.   Privileged  ports are those in the range 0 to
74       1023.  Only a privileged process (CAP_NET_BIND_SERVICE) is  allowed  to
75       bind  to a privileged port.  In the glibc implementation, this function
76       restricts its search to the ports from 512 to 1023.  The port  argument
77       is  value-result:  the  value  it  supplies  to the call is used as the
78       starting point for a circular search of the port range; on (successful)
79       return, it contains the port number that was bound to.
80
81   iruserok() and ruserok()
82       The  iruserok() and ruserok() functions take a remote host's IP address
83       or name, respectively, two usernames and a flag indicating whether  the
84       local  user's  name is that of the superuser.  Then, if the user is not
85       the superuser, it checks the /etc/hosts.equiv file.  If that lookup  is
86       not  done,  or  is  unsuccessful,  the .rhosts in the local user's home
87       directory is checked to see if the request for service is allowed.
88
89       If this file does not exist, is not a regular file, is owned by  anyone
90       other  than  the  user or the superuser, or is writable by anyone other
91       than the owner, the check automatically fails.  Zero is returned if the
92       machine  name is listed in the hosts.equiv file, or the host and remote
93       username are found  in  the  .rhosts  file;  otherwise  iruserok()  and
94       ruserok()  return  -1.   If the local domain (as obtained from gethost‐
95       name(2)) is the same as the remote domain, only the machine  name  need
96       be specified.
97
98       If  the  IP  address  of the remote host is known, iruserok() should be
99       used in preference to ruserok(), as it does not  require  trusting  the
100       DNS server for the remote host's domain.
101
102   *_af() variants
103       All  of the functions described above work with IPv4 (AF_INET) sockets.
104       The "_af" variants take  an  extra  argument  that  allows  the  socket
105       address  family  to be specified.  For these functions, the af argument
106       can be specified as AF_INET or AF_INET6.  In addition,  rcmd_af()  sup‐
107       ports the use of AF_UNSPEC.
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RETURN VALUE

110       The  rcmd()  function returns a valid socket descriptor on success.  It
111       returns -1 on error and prints a diagnostic  message  on  the  standard
112       error.
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114       The  rresvport()  function  returns a valid, bound socket descriptor on
115       success.  It returns -1 on  error  with  the  global  value  errno  set
116       according  to  the  reason for failure.  The error code EAGAIN is over‐
117       loaded to mean "All network ports in use."
118
119       For information on the return from ruserok() and iruserok(), see above.
120

VERSIONS

122       The   functions   iruserok_af(),   rcmd_af(),    rresvport_af(),    and
123       ruserok_af() functions are provide in glibc since version 2.2.
124

CONFORMING TO

126       Not in POSIX.1-2001.  Present on the BSDs, Solaris, and many other sys‐
127       tems.  These functions appeared in 4.2BSD.  The "_af" variants are more
128       recent additions, and are not present on as wide a range of systems.
129

BUGS

131       iruserok()  and  iruserok_af() are declared in glibc headers only since
132       version 2.12.
133

SEE ALSO

135       rlogin(1), rsh(1), intro(2), rexec(3), rexecd(8), rlogind(8), rshd(8)
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COLOPHON

138       This page is part of release 3.53 of the Linux  man-pages  project.   A
139       description  of  the project, and information about reporting bugs, can
140       be found at http://www.kernel.org/doc/man-pages/.
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144Linux                             2012-04-23                           RCMD(3)
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