Authen::Libwrap - access to Wietse Venema's TCP Wrappers library


  use Authen::Libwrap qw( hosts_ctl STRING_UNKNOWN );

  # we know the remote username (using identd)
  $rc = hosts_ctl(
  print "Access is ", $rc ? "granted" : "refused", "\n";

  # we don't know the remote username
  $rc = hosts_ctl(
  print "Access is ", $rc ? "granted" : "refused", "\n";

  # use a socket instead
  my $client = $listener->accept();
  $rc = hosts_ctl( "programname" $socket );
  print "Access is ", $rc ? "granted" : "refused", "\n";


The Authen::Libwrap module allows you to access the hosts_ctl() function from the popular TCP Wrappers security package. This allows validation of network access from perl programs against the system-wide hosts.allow file.

If any of the parameters to hosts_ctl() are not known (i.e. username due to lack of an identd server), the constant STRING_UNKNOWN may be passed to the function.


Authen::Libwrap has only one function, though it can be invoked in several ways. In each case, an true return code indicates that the connection is allowed per the rules in hosts.allow and an undef value indicates the opposite.

hosts_ctl($daemon, $hostname, $ip_addr, [ $user ] )

Takes three mandatory and one optional argument. $daemon is the service for which access is being requested (like 'ftpd' or 'sendmail'). $hostname is the name of the host requesting access. $ip_addr is the IP address of the host in dotted-quad notation. $user is the name of the user requesting access. If unknown, $user can be omitted; STRING_UNKNOWN will be passed in it's place.

hosts_ctl($daemon, $socket, [ $user ] )

If you have a socket (be it a glob, glob reference or an IO::Socket::INET, you can pass that as the second argument. The hostname and IP address will be determined using this socket. If the hostname or IP address cannot be determined from the socket, STRING_UNKNOWN will be passed in their place.


If you want to see the arguments that will be passed to the C function hosts_ctl(), set $Authen::Libwrap::DEBUG to a true value.


Nothing unless you ask for it.

hosts_ctl optionally



  • functions

  • constants

  • all

    everything the module has to offer.




Please report any bugs or feature requests (and a pull request for bonus points) through the issue tracker at

  • twist in hosts.allow

    Calls to hosts_ctl() which match a line in hosts.allow that uses the "twist" option will terminate the running perl program. This is not a bug in Authen::Libwrap per se -- libwrap uses exec(3) to replace the running process with the specified program, so there's nothing to return to.

    Some operating systems ship with a default catch-all rule in hosts.allow that uses the twist option. You may have to modify this configuration to use Authen::Libwrap effectively.

  • Test suite is not comprehensive

    The test suite isn't very comprehensive because the path to hosts.allow is set when libwrap is built and I can't tell what the user's rules are. I can make sure the function calls don't die, but I can't really tell if any call to hosts_ctl should give back a true or false value.


In early 2003 I was contacted by another Perl developer who had developed an XS interface to libwrap that covered more of the API than mine did. Originally he offered it as a patch to my module, but at the time I wasn't in a position to actively maintain anything on CPAN, so I suggested that he upload it himself. I unfortunately lost the email thread to a disk crash.

As of December 2003 I don't see any other modules professing to support libwrap om CPAN. If that person is still out there, please get in contact with me, otherwise I'll plan on implementing some of these TODOs in the new year:

  • provide support for hosts_access and request_* functions

  • develop an OO interface


Authen::Tcpdmatch, a Pure Perl module that can parse hosts.allow and hosts.deny if you don't need all the underlying features of libwrap.

hosts_access(3), hosts_access(5), hosts_options(5)

Wietse's tools and papers page:


James FitzGibbon, <>