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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 authen-tication authentication
     tication scheme based on reserved port numbers.  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 con-trol control
     trol process will return diagnostic output from the command (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 spec-ified. specified.
     ified.

     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 argument 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 families 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 success.  It returns -1 on error
     with the global value errno set according to the reason for failure.  The error code EAGAIN is over-loaded overloaded
     loaded 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. draft-ietf-ipngwgrfc2292bis-01.txt.
     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, draft-ietf-ipngwgrfc2292bis-01.txt,
     rfc2292bis-01.txt, and was implemented in the WIDE/KAME IPv6 protocol stack kit.  iruserok_sa()
     appeared in discussion on the IETF ipngwg mailing list, and was implemented in FreeBSD 4.0.

BSD                              March 3, 2000                             BSD

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