path: root/newlib/libc/sys/linux/net/rcmd.3

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

NAME
     rcmd, rresvport, iruserok, ruserok, rcmd_af, rresvport_af, iruserok_sa -- routines for re-
     turning 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 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 func-
     tions 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 connec-
     tion 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 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 at-
     tention 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 func-
     tions.  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 argument extension is implemented for func-
     tions that have no binary address argument.  Instead, the af argument specifies which ad-
     dress 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 ar-
     gument 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 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 im-
     plemented 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 mailing list, and was
     implemented in FreeBSD 4.0.

BSD                                       March 3, 2000                                       BSD