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RCMD
Section: Linux Programmer's Manual (3)
Updated: 2007-12-28
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NAME
rcmd, rresvport, iruserok, ruserok - routines for returning a
stream to a remote command
SYNOPSIS
#include <netdb.h> /* Or <unistd.h> on some systems */
int rcmd(char **ahost, int inport, const char *locuser,
const char *remuser, const char *cmd, int *fd2p);
int rresvport(int *port);
int iruserok(uint32_t raddr, int superuser,
const char *ruser, const char *luser);
int ruserok(const char *rhost, int superuser,
const char *ruser, const char *luser);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
rcmd(),
rresvport(),
ruserok():
_BSD_SOURCE
DESCRIPTION
The
rcmd()
function is used by the superuser to execute a command on
a remote machine using an authentication scheme based
on privileged port numbers.
The
rresvport()
function
returns a descriptor to a socket
with an address in the privileged port space.
The
iruserok()
and
ruserok()
functions are used by servers
to authenticate clients requesting service with
rcmd().
All four 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 nonzero, 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
address 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 superuser 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, respectively,
two usernames and a flag indicating whether the local user's
name is that of the superuser.
Then, if the user is
not
the superuser, 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 superuser, 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 username are found in the
.rhosts
file; otherwise
iruserok()
and
ruserok()
return -1.
If the local domain (as obtained from
gethostname(2))
is the same as the remote domain, only the machine name need be specified.
If the IP address of the remote host is known,
iruserok()
should be used in preference to
ruserok(),
as it does not require trusting the DNS server for the remote host's domain.
RETURN VALUE
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."
CONFORMING TO
Not in POSIX.1-2001.
Present on the BSDs, Solaris, and many other systems.
These
functions appeared in
4.2BSD.
BUGS
iruserok()
is not declared in glibc headers.
SEE ALSO
rlogin(1),
rsh(1),
intro(2),
rexec(3),
rexecd(8),
rlogind(8),
rshd(8)
COLOPHON
This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- CONFORMING TO
-
- BUGS
-
- SEE ALSO
-
- COLOPHON
-
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