1RCMD(3)                  BSD Library Functions Manual                  RCMD(3)
2

NAME

4     rcmd, rresvport, iruserok, ruserok — routines for returning a stream to a
5     remote command
6

SYNOPSIS

8     #include <netdb.h>   /* Or <unistd.h> on some systems */
9
10     int
11     rcmd(char **ahost, int inport, const char *locuser, const char *remuser,
12         const char *cmd, int *fd2p);
13
14     int
15     rresvport(int *port);
16
17     int
18     iruserok(u_int32_t raddr, int superuser, const char *ruser,
19         const char *luser);
20
21     int
22     ruserok(const char *rhost, int superuser, const char *ruser,
23         const char *luser);
24

DESCRIPTION

26     The rcmd() function is used by the superuser to execute a command on a
27     remote machine using an authentication scheme based on reserved port num‐
28     bers.  The rresvport() function returns a descriptor to a socket with an
29     address in the privileged port space.  The iruserok() and ruserok() func‐
30     tions are used by servers to authenticate clients requesting service with
31     rcmd().  All four functions are present in the same file and are used by
32     the rshd(8) server (among others).
33
34     The rcmd() function looks up the host *ahost using gethostbyname(3),
35     returning -1 if the host does not exist.  Otherwise *ahost is set to the
36     standard name of the host and a connection is established to a server
37     residing at the well-known Internet port inport.
38
39     If the connection succeeds, a socket in the Internet domain of type
40     SOCK_STREAM is returned to the caller, and given to the remote command as
41     stdin and stdout.  If fd2p is non-zero, then an auxiliary channel to a
42     control process will be set up, and a descriptor for it will be placed in
43     *fd2p.  The control process will return diagnostic output from the com‐
44     mand (unit 2) on this channel, and will also accept bytes on this channel
45     as being UNIX signal numbers, to be forwarded to the process group of the
46     command.  If fd2p is 0, then the stderr (unit 2 of the remote command)
47     will be made the same as the stdout and no provision is made for sending
48     arbitrary signals to the remote process, although you may be able to get
49     its attention by using out-of-band data.
50
51     The protocol is described in detail in rshd(8).
52
53     The rresvport() function is used to obtain a socket with a privileged
54     address bound to it.  This socket is suitable for use by rcmd() and sev‐
55     eral other functions.  Privileged Internet ports are those in the range 0
56     to 1023.  Only the superuser is allowed to bind an address of this sort
57     to a socket.
58
59     The iruserok() and ruserok() functions take a remote host's IP address or
60     name, respectively, two user names and a flag indicating whether the
61     local user's name is that of the superuser.  Then, if the user is NOT the
62     superuser, it checks the /etc/hosts.equiv file.  If that lookup is not
63     done, or is unsuccessful, the .rhosts in the local user's home directory
64     is checked to see if the request for service is allowed.
65
66     If this file does not exist, is not a regular file, is owned by anyone
67     other than the user or the superuser, or is writable by anyone other than
68     the owner, the check automatically fails.  Zero is returned if the
69     machine name is listed in the “hosts.equiv” file, or the host and remote
70     user name are found in the “.rhosts” file; otherwise iruserok() and
71     ruserok() return -1.  If the local domain (as obtained from
72     gethostname(2)) is the same as the remote domain, only the machine name
73     need be specified.
74
75     If the IP address of the remote host is known, iruserok() should be used
76     in preference to ruserok(), as it does not require trusting the DNS
77     server for the remote host's domain.
78

DIAGNOSTICS

80     The rcmd() function returns a valid socket descriptor on success.  It
81     returns -1 on error and prints a diagnostic message on the standard
82     error.
83
84     The rresvport() function returns a valid, bound socket descriptor on suc‐
85     cess.  It returns -1 on error with the global value errno set according
86     to the reason for failure.  The error code EAGAIN is overloaded to mean
87     ``All network ports in use.''
88

CONFORMING TO

90     Not in POSIX.1-2001.  Present on the BSDs, Solaris, and many other sys‐
91     tems.  These functions appeared in 4.2BSD.
92

SEE ALSO

94     rlogin(1), rsh(1), intro(2), rexec(3), rexecd(8), rlogind(8), rshd(8)
95
964.2BSD                           June 4, 1993                           4.2BSD
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