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rcmd(3)                  BSD Library Functions Manual                  rcmd(3)


NAME

     rcmd, rresvport, iruserok, ruserok, rcmd_af, rresvport_af, iruserok_sa --
     routines for returning a stream to a remote command


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <unistd.h>

     int
     rcmd(char **ahost, int inport, const char *locuser, const char *remuser,
         const char *cmd, int *fd2p);

     int
     rresvport(int *port);

     int
     iruserok(u_long raddr, int superuser, const char *ruser,
         const char *luser);

     int
     ruserok(const char *rhost, int superuser, const char *ruser,
         const char *luser);

     int
     rcmd_af(char **ahost, int inport, const char *locuser,
         const char *remuser, const char *cmd, int *fd2p, int af);

     int
     rresvport_af(int *port, int af);

     int
     iruserok_sa(const void *addr, int addrlen, int superuser,
         const char *ruser, const char *luser);


DESCRIPTION

     The rcmd() function is used by the super-user to execute a command on a
     remote machine using an authentication scheme based on reserved port num-
     bers.  The rresvport() function returns a descriptor to a socket with an
     address in the privileged port space.  The ruserok() function is used by
     servers to authenticate clients requesting service with rcmd().  All
     three functions are present in the same file and are used by the rshd(8)
     server (among others).

     The rcmd() function looks up the host *ahost using gethostbyname(3),
     returning -1 if the host does not exist.  Otherwise *ahost is set to the
     standard name of the host and a connection is established to a server
     residing at the well-known Internet port inport.

     If the connection succeeds, a socket in the Internet domain of type
     SOCK_STREAM is returned to the caller, and given to the remote command as
     stdin and stdout.  If fd2p is non-zero, then an auxiliary channel to a
     control process will be set up, and a descriptor for it will be placed in
     *fd2p.  The control process will return diagnostic output from the com-
     mand (unit 2) on this channel, and will also accept bytes on this channel
     as being UNIX signal numbers, to be forwarded to the process group of the
     command.  If fd2p is 0, then the stderr (unit 2 of the remote command)
     will be made the same as the stdout and no provision is made for sending
     arbitrary signals to the remote process, although you may be able to get
     its attention by using out-of-band data.

     The protocol is described in detail in rshd(8).

     The rresvport() function is used to obtain a socket to which an address
     with a Privileged Internet port is bound.  This socket is suitable for
     use by rcmd() and several other functions.  Privileged Internet ports are
     those in the range 0 to 1023.  Only the super-user is allowed to bind an
     address of this sort to a socket.

     The iruserok() and ruserok() functions take a remote host's IP address or
     name, as returned by the gethostbyname(3) routines, two user names and a
     flag indicating whether the local user's name is that of the super-user.
     Then, if the user is NOT the super-user, it checks the /etc/hosts.equiv
     file.  If that lookup is not done, or is unsuccessful, the .rhosts in the
     local user's home directory is checked to see if the request for service
     is allowed.

     If this file does not exist, is not a regular file, is owned by anyone
     other than the user or the super-user, or is writable by anyone other
     than the owner, the check automatically fails.  Zero is returned if the
     machine name is listed in the ``hosts.equiv'' file, or the host and
     remote user name are found in the ``.rhosts'' file; otherwise iruserok()
     and ruserok() return -1.  If the local domain (as obtained from
     gethostname(3)) is the same as the remote domain, only the machine name
     need be specified.

     The iruserok() function is strongly preferred for security reasons.  It
     requires trusting the local DNS at most, while the ruserok() function
     requires trusting the entire DNS, which can be spoofed.

     The functions with an ``_af'' or ``_sa'' suffix, i.e., rcmd_af(),
     rresvport_af() and iruserok_sa(), work the same as the corresponding
     functions without a suffix, except that they are capable of handling both
     IPv6 and IPv4 ports.

     The ``_af'' suffix means that the function has an additional af argument
     which is used to specify the address family, (see below).  The af argu-
     ment extension is implemented for functions that have no binary address
     argument.  Instead, the af argument specifies which address family is
     desired.

     The ``_sa'' suffix means that the function has general socket address and
     length arguments.  As the socket address is a protocol independent data
     structure, IPv4 and IPv6 socket address can be passed as desired.  The sa
     argument extension is implemented for functions that pass a protocol
     dependent binary address argument.  The argument needs to be replaced
     with a more general address structure to support multiple address fami-
     lies in a general way.

     The functions with neither an ``_af'' suffix nor an ``_sa'' suffix work
     for IPv4 only, except for ruserok() which can handle both IPv6 and IPv4.
     To switch the address family, the af argument must be filled with
     AF_INET, or AF_INET6.  For rcmd_af(), PF_UNSPEC is also allowed.


DIAGNOSTICS

     The rcmd() function returns a valid socket descriptor on success.  It
     returns -1 on error and prints a diagnostic message on the standard
     error.

     The rresvport() function returns a valid, bound socket descriptor on suc-
     cess.  It returns -1 on error with the global value errno set according
     to the reason for failure.  The error code EAGAIN is overloaded to mean
     ``All network ports in use.''


SEE ALSO

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

     W. Stevens and M. Thomas, Advanced Socket API for IPv6, RFC2292.

     W. Stevens, M. Thomas, and E. Nordmark, Advanced Socket API for IPv6,
     draft-ietf-ipngwg-rfc2292bis-01.txt.


HISTORY

     Most of these functions appeared in 4.2BSD.  rresvport_af() appeared in
     RFC2292, and was implemented by the WIDE project for the Hydrangea IPv6
     protocol stack kit.  rcmd_af() appeared in draft-ietf-ipngwg-
     rfc2292bis-01.txt, and was implemented in the WIDE/KAME IPv6 protocol
     stack kit.  iruserok_sa() appeared in discussion on the IETF ipngwg mail-
     ing list, and was implemented in FreeBSD 4.0.

BSD                              March 3, 2000                             BSD

Mac OS X 10.6 - Generated Thu Sep 17 20:22:27 CDT 2009
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