from small one page howto to huge articles all in one place
 

search text in:





Poll
Which kernel version do you use?





poll results

Last additions:
using iotop to find disk usage hogs

using iotop to find disk usage hogs

words:

887

views:

85981

userrating:

average rating: 1.7 (82 votes) (1=very good 6=terrible)


May 25th. 2007:
Words

486

Views

202346

why adblockers are bad


Workaround and fixes for the current Core Dump Handling vulnerability affected kernels

Workaround and fixes for the current Core Dump Handling vulnerability affected kernels

words:

161

views:

84336

userrating:

average rating: 1.3 (27 votes) (1=very good 6=terrible)


April, 26th. 2006:

Druckversion
You are here: manpages





RCMD

Section: Linux Programmer's Manual (3)
Updated: 2014-05-28
Index Return to Main Contents
 

NAME

rcmd, rresvport, iruserok, ruserok, rcmd_af, rresvport_af, iruserok_af, ruserok_af - routines for returning a stream to a remote command  

SYNOPSIS

#include <netdb.h>   /* Or <unistd.h> on some systems */

int rcmd(char **ahost, unsigned short inport, const char *locuser, 
         const char *remuser, const char *cmd, int *fd2p);

int rresvport(int *port);

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 rcmd_af(char **ahost, unsigned short inport, const char *locuser, 
            const char *remuser, const char *cmd, int *fd2p,
            sa_family_t af);

int rresvport_af(int *port, sa_family_t af);

int iruserok_af(const void *raddr, int superuser, 
                const char *ruser, const char *luser, sa_family_t af);

int ruserok_af(const char *rhost, int superuser, 
               const char *ruser, const char *luser, sa_family_t af);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

rcmd(), rcmd_af(), rresvport(), rresvport_af(), iruserok(), iruserok_af(), ruserok(), ruserok_af(): _BSD_SOURCE  

DESCRIPTION

The rcmd() function is used by the superuser to execute a command on a remote machine using an authentication scheme based on privileged 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 used by the rshd(8) server (among others).  

rcmd()

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 nonzero, 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).  

rresvport()

The rresvport() function is used to obtain a socket with a privileged port bound to it. This socket is suitable for use by rcmd() and several other functions. Privileged ports are those in the range 0 to 1023. Only a privileged process (CAP_NET_BIND_SERVICE) is allowed to bind to a privileged port. In the glibc implementation, this function restricts its search to the ports from 512 to 1023. The port argument is value-result: the value it supplies to the call is used as the starting point for a circular search of the port range; on (successful) return, it contains the port number that was bound to.  

iruserok() and ruserok()

The iruserok() and ruserok() functions take a remote host's IP address or name, respectively, two usernames and a flag indicating whether the local user's name is that of the superuser. Then, if the user is not the superuser, 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 superuser, 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 username 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.  

*_af() variants

All of the functions described above work with IPv4 (AF_INET) sockets. The "_af" variants take an extra argument that allows the socket address family to be specified. For these functions, the af argument can be specified as AF_INET or AF_INET6. In addition, rcmd_af() supports the use of AF_UNSPEC.  

RETURN VALUE

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."

For information on the return from ruserok() and iruserok(), see above.  

VERSIONS

The functions iruserok_af(), rcmd_af(), rresvport_af(), and ruserok_af() functions are provide in glibc since version 2.2.  

CONFORMING TO

Not in POSIX.1-2001. Present on the BSDs, Solaris, and many other systems. These functions appeared in 4.2BSD. The "_af" variants are more recent additions, and are not present on as wide a range of systems.  

BUGS

iruserok() and iruserok_af() are declared in glibc headers only since version 2.12.  

SEE ALSO

rlogin(1), rsh(1), intro(2), rexec(3), rexecd(8), rlogind(8), rshd(8)  

COLOPHON

This page is part of release 3.81 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
SYNOPSIS
DESCRIPTION
rcmd()
rresvport()
iruserok() and ruserok()
*_af() variants
RETURN VALUE
VERSIONS
CONFORMING TO
BUGS
SEE ALSO
COLOPHON


Please read "Why adblockers are bad".



Other free services
toURL.org
Shorten long
URLs to short
links like
http://tourl.org/2
tourl.org
.
Reverse DNS lookup
Find out which hostname(s)
resolve to a
given IP or other hostnames for the server
www.reversednslookup.org
rdf newsfeed | rss newsfeed | Atom newsfeed
- Powered by LeopardCMS - Running on Gentoo -
Copyright 2004-2013 Sascha Nitsch Unternehmensberatung UG(haftungsbeschränkt)
Valid XHTML1.1 : Valid CSS : buttonmaker
- Level Triple-A Conformance to Web Content Accessibility Guidelines 1.0 -
- Copyright and legal notices -
Time to create this page: 4.4 ms