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rexec() function problem


 
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Top Forums Programming rexec() function problem
# 8  
Old 01-08-2002
Quote:
WARNINGS
There is no way to specify options to the socket() call that rexec()
makes.

A program using rexec() should not be put in the background when
rexec() is expected to prompt for a password or user name. Putting
rexec() in the background will cause it to compete with the current
shell process for input.

Since rexec() replaces the pointer to the host name (*ahost) with a
pointer to the standard name of the host in a static data area, this
value must be copied into the user's data area if it is to be used
later.


The password is sent unencrypted through the socket connection.

Last edited by shaik786; 01-08-2002 at 10:25 AM..
shaik786
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REXEC(3)						     Linux Programmer's Manual							  REXEC(3)

NAME
rexec, rexec_af - return stream to a remote command SYNOPSIS
#define _BSD_SOURCE /* See feature_test_macros(7) */ #include <netdb.h> int rexec(char **ahost, int inport, char *user, char *passwd, char *cmd, int *fd2p); int rexec_af(char **ahost, int inport, char *user, char *passwd, char *cmd, int *fd2p, sa_family_t af); DESCRIPTION
This interface is obsoleted by rcmd(3). The rexec() 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. If a username and password are both specified, then these are used to authenticate to the foreign host; otherwise the environment and then the user's .netrc file in his home directory are searched for appropriate information. If all this fails, the user is prompted for the information. The port inport specifies which well-known DARPA Internet port to use for the connection; the call getservbyname("exec", "tcp") (see get- servent(3)) will return a pointer to a structure that contains the necessary port. The protocol for connection is described in detail in rexecd(8). 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 setup, 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. The diagnostic information returned does not include remote authorization failure, as the secondary connection is set up after authorization has been verified. 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. rexec_af() The rexec() function works over IPv4 (AF_INET). By contrast, the rexec_af() function provides an extra argument, af, that allows the call- er to select the protocol. This argument can be specified as AF_INET, AF_INET6, or AF_UNSPEC (to allow the implementation to select the protocol). VERSIONS
The rexec_af() function was added to glibc in version 2.2. ATTRIBUTES
Multithreading (see pthreads(7)) The rexec() and rexec_af() functions are not thread-safe. CONFORMING TO
These functions are not in POSIX.1-2001. The rexec() function first appeared in 4.2BSD, and is present on the BSDs, Solaris, and many other systems. The rexec_af() function is more recent, and less widespread. BUGS
The rexec() function sends the unencrypted password across the network. The underlying service is considered a big security hole and therefore not enabled on many sites; see rexecd(8) for explanations. SEE ALSO
rcmd(3), rexecd(8) COLOPHON
This page is part of release 3.53 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/. Linux 2013-07-04 REXEC(3)

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