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Top Forums UNIX for Dummies Questions & Answers /etc/hosts.deny Post 302948743 by RavinderSingh13 on Thursday 2nd of July 2015 02:40:36 AM

07-02-2015

Moderator

Hello Alvinoo,

Just want to add a little more here. To restrict access to your Unix or Linux machine, you must modify the /etc/hosts.allow and /etc/host.deny files. These files are used by the tcpd (tcp wrapper) and sshd programs to decide whether or not to accept a connection coming in from another IP address. ITS recommends that to start with, you restrict access to only those network addresses you are certain should be allowed access. The following two example files allow connections from any address in the virginia.edu network domain, but no others.

Following is an example for same.
/etc/hosts.allow

Code:

 #
 # hosts.allow   This file describes the names of 
 #               the hosts that are allowed to use 
 #               the local INET services, as decided
 #               by the '/usr/sbin/tcpd' server.
 #
 # Only allow connections within the virginia.edu 
 # domain.

ALL: .virginia.edu

Code:

 #
 # hosts.deny    This file describes the names of
 #               the hosts that are *not* allowed 
 #               to use the local INET services, as 
 #               decided by the '/usr/sbin/tcpd' 
 #               server.
 #
 # deny all by default, only allowing hosts or 
 # domains listed in hosts.allow.
 
 ALL: ALL

Configuration shown in the above /etc/hosts.allow file, to permit connections to any services protected by the tcpd or sshd from only systems within the virginia.edu domain. Also for more information on same, you can go through the following link too.
hosts.deny(5) - Linux man page

Hope this helps.

Thanks,
R. Singh

Last edited by RavinderSingh13; 07-02-2015 at 03:45 AM..

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LEARN ABOUT NETBSD

tcpdchk

TCPDCHK(8)						      System Manager's Manual							TCPDCHK(8)

NAME

       tcpdchk - tcp wrapper configuration checker

SYNOPSIS

       tcpdchk [-a] [-d] [-i inet_conf] [-v]

DESCRIPTION

       tcpdchk	examines  your	tcp  wrapper  configuration and reports all potential and real problems it can find. The program examines the tcpd
       access control files (by default, these are /etc/hosts.allow and /etc/hosts.deny), and compares the entries in these files against  entries
       in the inetd or tlid network configuration files.

       tcpdchk reports problems such as non-existent pathnames; services that appear in tcpd access control rules, but are not controlled by tcpd;
       services that should not be wrapped; non-existent host names or non-internet address forms; occurrences of host aliases instead of official
       host names; hosts with a name/address conflict; inappropriate use of wildcard patterns; inappropriate use of NIS netgroups or references to
       non-existent NIS netgroups; references to non-existent options; invalid arguments to options; and so on.

       Where possible, tcpdchk provides a helpful suggestion to fix the problem.

OPTIONS

       -a     Report access control rules that permit access without an explicit ALLOW keyword. This applies only when the extended access control
	      language is enabled (build with -DPROCESS_OPTIONS).

       -d     Examine hosts.allow and hosts.deny files in the current directory instead of the default ones.

       -i inet_conf
	      Specify this option when tcpdchk is unable to find your inetd.conf or tlid.conf network configuration file, or when you suspect that
	      the program uses the wrong one.

       -v     Display the contents of each access control rule.  Daemon lists, client lists, shell commands and options are  shown  in	a  pretty-
	      printed format; this makes it easier for you to spot any discrepancies between what you want and what the program understands.

FILES

       The default locations of the tcpd access control tables are:

       /etc/hosts.allow
       /etc/hosts.deny

SEE ALSO

       tcpdmatch(8), explain what tcpd would do in specific cases.
       hosts_access(5), format of the tcpd access control tables.
       hosts_options(5), format of the language extensions.
       inetd.conf(5), format of the inetd control file.

AUTHORS

       Wietse Venema (wietse@wzv.win.tue.nl),
       Department of Mathematics and Computing Science,
       Eindhoven University of Technology
       Den Dolech 2, P.O. Box 513,
       5600 MB Eindhoven, The Netherlands

																	TCPDCHK(8)

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