blackhole(6) [debian man page]

blackhole(6)							   Games Manual 						      blackhole(6)

NAME

       blackhole, mori1, mori2, yasiti - draws funny things on an XDisplay

SYNOPSIS

       blackhole [-display <displayname>]

DESCRIPTION

       blackhole
	      produces an animated zoom-out effect on a display. The display will be restored afterwards.

       mori1  tiles a display with the face of a girl winking at you. The display will be restored afterwards.

       mori2  displays the face of a girl winking at you. The display will be restored afterwards.

       yasiti displays a rotating black object at the center of the screen. The display will be restored afterwards.

OPTIONS

       -display displayname
	      With  this  argument  you  can determine on which display the programs should draw. By default, the display specified by the DISPLAY
	      environment variable is used.

SEE ALSO

       X(7)

AUTHOR

       This manual page was written by Timo Schneider <timo.schneider@s2004.tu-chemnitz.de>, for the Debian project (but may be used by others).

																      blackhole(6)

BLACKHOLE(4)						   BSD Kernel Interfaces Manual 					      BLACKHOLE(4)

NAME

     blackhole -- a sysctl(8) MIB for manipulating behaviour in respect of refused TCP or UDP connection attempts

SYNOPSIS

     sysctl net.inet.tcp.blackhole[=[0 | 1 | 2]]
     sysctl net.inet.udp.blackhole[=[0 | 1]]

DESCRIPTION

     The blackhole sysctl(8) MIB is used to control system behaviour when connection requests are received on TCP or UDP ports where there is no
     socket listening.

     Normal behaviour, when a TCP SYN segment is received on a port where there is no socket accepting connections, is for the system to return a
     RST segment, and drop the connection.  The connecting system will see this as a ``Connection refused''.  By setting the TCP blackhole MIB to
     a numeric value of one, the incoming SYN segment is merely dropped, and no RST is sent, making the system appear as a blackhole.  By setting
     the MIB value to two, any segment arriving on a closed port is dropped without returning a RST.  This provides some degree of protection
     against stealth port scans.

     In the UDP instance, enabling blackhole behaviour turns off the sending of an ICMP port unreachable message in response to a UDP datagram
     which arrives on a port where there is no socket listening.  It must be noted that this behaviour will prevent remote systems from running
     traceroute(8) to a system.

     The blackhole behaviour is useful to slow down anyone who is port scanning a system, attempting to detect vulnerable services on a system.
     It could potentially also slow down someone who is attempting a denial of service attack.

WARNING

     The TCP and UDP blackhole features should not be regarded as a replacement for firewall solutions.  Better security would consist of the
     blackhole sysctl(8) MIB used in conjunction with one of the available firewall packages.

     This mechanism is not a substitute for securing a system.	It should be used together with other security mechanisms.

SEE ALSO

     ip(4), tcp(4), udp(4), ipf(8), ipfw(8), pfctl(8), sysctl(8)

HISTORY

     The TCP and UDP blackhole MIBs first appeared in FreeBSD 4.0.

AUTHORS

     Geoffrey M. Rehmet

BSD
								  January 1, 2007							       BSD