NAME
rcmd
, orcmd
,
rcmd_af
, orcmd_af
,
rresvport
, rresvport_af
,
iruserok
, ruserok
,
iruserok_sa
—
routines for returning a stream to a
remote command
LIBRARY
library “libc”
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
Thercmd
()
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.