Originální popis anglicky:
rcmd,
rresvport,
iruserok,
ruserok
—
routines for returning a stream to a
remote command
Návod, kniha: Library Functions Manual
#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_int32_t
raddr,
int
superuser,
const
char *ruser,
const char
*luser);
int
ruserok(
const
char *rhost,
int
superuser,
const
char *ruser,
const char
*luser);
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
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 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 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 writeable 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(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.
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.''
rlogin(1),
rsh(1),
intro(2),
rexec(3),
rexecd(8),
rlogind(8),
rshd(8)
These functions appeared in
4.2BSD.
