NAME
rcmd,
orcmd,
rcmd_af,
orcmd_af,
rresvport,
rresvport_af,
iruserok,
ruserok,
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
orcmd(
char
**ahost,
int inport,
const char *locuser,
const char *remuser,
const char *cmd,
int *fd2p);
int
rcmd_af(
char
**ahost,
int inport,
const char *locuser,
const char *remuser,
const char *cmd,
int *fd2p,
int af);
int
orcmd_af(
char
**ahost,
int inport,
const char *locuser,
const char *remuser,
const char *cmd,
int *fd2p,
int af);
int
rresvport(
int
*port);
int
rresvport_af(
int
*port,
int family);
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);
int
iruserok_sa(
const
void *raddr,
int
rlen,
int superuser,
const char *ruser,
const char *luser);
DESCRIPTION
The
rcmd() function is available for use by anyone to run
commands on a remote system. It acts like the
orcmd()
command, with the exception that it makes a call out to the
rcmd(1) command, or any other
user-specified command, to perform the actual connection (thus not requiring
that the caller be running as the super-user), and is only available for the
“shell/tcp” port. The
orcmd() function is used
by the super-user to execute a command on a remote machine using an
authentication scheme based on reserved port numbers. While
rcmd() and
orcmd() can only handle IPv4
address in the first argument,
rcmd_af() and
orcmd_af() can handle other cases as well. The
rresvport() function returns a descriptor to a socket with
an address in the privileged port space. The
rresvport_af()
function is similar to
rresvport(), but you can explicitly
specify the address family to use. Calling
rresvport_af()
with
AF_INET
has the same effect as
rresvport(). The
iruserok() and
ruserok() functions are used by servers to authenticate
clients requesting service with
rcmd(). All six functions
are present in the same file and are used by the
rshd(8) server (among others).
iruserok_sa() is an address family independent variant of
iruserok().
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 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.
rcmd_af() and
orcmd_af() take address family
in the last argument. If the last argument is
PF_UNSPEC
, interpretation of
*ahost will obey the underlying address resolution like
DNS.
The protocol is described in detail in
rshd(8).
The
rresvport() and
rresvport_af() functions
are 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
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, 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
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.
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.
While
iruserok() can handle IPv4 addresses only,
iruserok_sa() and
ruserok() can handle
other address families as well, like IPv6. The first argument of
iruserok_sa() is typed as
void * to
avoid dependency between
<unistd.h>
and
<sys/socket.h>.
ENVIRONMENT
RCMD_CMD
- When using the rcmd() function, this
variable is used as the program to run instead of
rcmd(1).
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() and
rresvport_af() function
return a valid, bound socket descriptor on success. They return -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
rcmd(1),
rlogin(1),
rsh(1),
intro(2),
rexec(3),
hosts.equiv(5),
rhosts(5),
rexecd(8),
rlogind(8),
rshd(8)
HISTORY
The
orcmd(),
rresvport(),
iruserok() and
ruserok() functions
appeared in
4.2BSD, where the
orcmd() function was called
rcmd(). The
(newer)
rcmd() function appeared in
NetBSD
1.3.
rcmd_af() and
rresvport_af()
were defined in RFC2292.