rcmd.3x

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)rcmd.3x	8.1	9/11/90
.TH rcmd 3x
.SH Name
rcmd, rresvport, ruserok \- routines for returning a stream to a remote command
.SH Syntax
.nf
.B "rem = rcmd(\fIahost, inport, locuser, remuser, cmd, fd2p\fP);"
.B char \fI**ahost\fP;
.B u_short \fIinport\fP;
.B "char \fI*locuser, *remuser, *cmd\fP;"
.B int \fI*fd2p\fP;
.PP
.B s = rresvport(\fIport)\fP;
.B int \fI*port\fP;
.PP
.B "ruserok(\fIrhost, superuser, ruser, luser\fP)"
.B char \fI*rhost\fP;
.B int \fIsuperuser\fP;
.B char \fI*ruser, *luser\fP;
.fi
.SH Description
.NXR "rcmd subroutine"
.NXR "rresvport subroutine"
.NXR "ruserok subroutine"
.NXAM "rmt program" "rcmd subroutine"
.NXR "stream" "returning to remote command"
The
.PN rcmd
subroutine
is used by the superuser to execute a command on
a remote machine using an authentication scheme based
on reserved port numbers.  The
.PN rresvport
subroutine
is a routine that returns a descriptor to a socket
with an address in the privileged port space.
The
.PN ruserok
subroutine
is a routine used by servers
to authenticate clients requesting service with
.PN rcmd .
All three functions are present in the same file and are used
by the
.MS rshd 8c 
server (among others).
.PP
The
.PN rcmd
subroutine looks up the host
.I *ahost
using
.MS gethostbyname 3n ,
returning \-1 if the host does not exist.
For further information, see 
.MS gethostent 3n .
Otherwise
.I *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
.IR inport .
.PP
If the call succeeds, a socket of type SOCK_STREAM
is returned to the caller and given to the remote
command as 
.B stdin
and
.B stdout.
If
.I fd2p
is nonzero, then an auxiliary channel to a control
process will be set up, and a descriptor for it will be placed
in
.IR *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
.I fd2p
is 0, then the 
.B stderr
(unit 2 of the remote
command) will be made the same as the 
.B 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.
.PP
The protocol is described in detail in 
.MS rshd 8c .
.PP
The
.PN rresvport
subroutine is used to obtain a socket with a privileged
address bound to it.  This socket is suitable for use
by 
.PN rcmd
and several other routines.  Privileged addresses consist
of a port in the range 0 to 1023.  Only the superuser
is allowed to bind an address of this sort to a socket.
.PP
The
.PN ruserok
subroutine takes a remote host's name, as returned by a
.MS gethostent 3n 
routine, two user names and a flag indicating if
the local user's name is the superuser.  It then
checks the files 
.PN /etc/hosts.equiv
and 
.PN \&.rhosts
in the user's home directory to see if the request for
service is allowed.  A 0 is returned if the machine
name is listed in the 
.PN hosts.equiv 
file, or the
host and remote user name are found in the 
.PN \&.rhosts
file.  Otherwise 
.PN ruserok
returns \-1.  If the superuser
flag is 1, the checking of the 
.PN hosts.equiv 
file is
bypassed.
.SH See Also
rlogin(1c), rsh(1c), gethostent(3n), rexec(3x), rexecd(8c), 
rlogind(8c), rshd(8c)