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)
Check Out this Related Man Page
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 conjuction 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
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