RCMD(3) BSD Programmer's Manual RCMD(3)
NAME
rcmd, rresvport, ruserok - routines for returning a stream to a remote
command
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
ruserok(const char *rhost, 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), re-
turning -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 re-
siding 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 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 with a privileged ad-
dress bound to it. 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 ruserok() argument takes a remote host's name, as returned by the
gethostbyaddr(3) routine, 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 files /etc/hosts.equiv. If that lookup
is not done, or is unsuccessful, the .rhosts in the local user's home di-
rectory is checked to see if the request for service is allowed. If this
file is owned by anyone other than the user or the super-user, or if it
is writeable by anyone other than the owner, the check automatically
fails. A 0 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 ruserok() returns -1. If the local domain
(as obtained from gethostname(2)) is the same as the remote domain, only
the machine name need be specified.
DIAGNOSTICS
The rcmd() function returns a valid socket descriptor on success. It re-
turns -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)
HISTORY
These functions appeared in 4.2BSD.
4.2 Berkeley Distribution March 26, 1993 2