rcmd(3) -- Linux man page
- routines for returning a stream to a remote command
Fd #include <unistd.h>
Fn rcmd char **ahost int inport const char *locuser const char *remuser const char *cmd int *fd2p
Fn rresvport int *port
Fn iruserok u_int32_t raddr int superuser const char *ruser const char *luser
Fn ruserok const char *rhost int superuser const char *ruser const char *luser
is used by the super-user to execute a command on
a remote machine using an authentication scheme based
on reserved port numbers.
returns a descriptor to a socket
with an address in the privileged port space.
functions are used by servers
to authenticate clients requesting service with
Fn rcmd .
All four functions are present in the same file and are used
server (among others).
looks up the host
returning -1 if the host does not exist.
is set to the standard name of the host
and a connection is established to a server
residing at the well-known Internet port
Fa inport .
If the connection succeeds,
a socket in the Internet domain of type
is returned to the caller, and given to the remote
is non-zero, then an auxiliary channel to a control
process will be set up, and a descriptor for it will be placed
Fa *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
signal numbers, to be
forwarded to the process group of the command.
is 0, then the
(unit 2 of the remote
command) will be made the same as the
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
function is used to obtain a socket with a privileged
address bound to it. This socket is suitable for use
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.
functions take a remote host's IP address or name, respectively,
two user names and a flag indicating whether the local user's
name is that of the super-user.
Then, if the user is
the super-user, it checks the
If that lookup is not done, or is unsuccessful, the
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 writeable by anyone other
than the owner, the check automatically fails.
Zero is returned if the machine name is listed in the
file, or the host and remote user name are found in the
If the local domain (as obtained from
is the same as the remote domain, only the machine name need be specified.
If the IP address of the remote host is known,
should be used in preference to
Fn ruserok ,
as it does not require trusting the DNS server for the remote host's domain.
returns a valid socket descriptor on success.
It returns -1 on error and prints a diagnostic message on the standard error.
returns a valid, bound socket descriptor on success.
It returns -1 on error with the global value
set according to the reason for failure.
The error code
is overloaded to mean ``All network ports in use.''
functions appeared in