Multiple ipv6 addresses on an interface

To prevent being tracked on the intertubes, ipv6 has security extensions that, (if they are enabled via sysctl net.ipv6.conf.all somewhere), from time to time creates random a address, and expire the old ones for outgoing traffic. To see the addresses do

ip -6 addr

and look for temporary.  The expired addresses (that still work) have the word "deprecated".  If you get sick of seeing them, delete an address from an interface with

ip -6 addr del dev eth0

or delete all deprecated addresses like this

ip -6 addr | awk '/deprecated/ {print "ip -6 addr del " $2 " dev eth0"}' | sudo bash -s

Virtual X11 display

x11vnc -create -forever -localhost

-create launches Xvfb  (on DISPLAY=:20 or something like that)
-forever enables reconnection
-localhost only listens to local connections, so you'll have to forward the port (5900+nr) for instance over ssh.

Then one may need a windowmanager too, for instance

DISPLAY=:10 fluxbox

You may put fluxbox in the .xinitrc file too.

posting to xen-devel

example

git format-patch 73edc26b69803cdbce62513c7be8010c829e4274^..73edc26b69803cdbce62513c7be8010c829e4274

git send-email --in-reply-to '<1358428780 .13856.57.camel=".13856.57.camel" zakaz.uk.xensource.com="zakaz.uk.xensource.com">' --from lra@sics.se --to xen-devel@lists.xensource.com --smtp-server smtp.sics.se  0001-Set-register-values-and-comment-in-early-init_uart-t.patch

inplace quicksort in python

https://gist.github.com/4537928


def quicksort(l):
work = [(0,len(l)-1)]
while work:
(left,right) = work.pop()
if right < left: 
continue
i_piv = left
piv = l[i_piv]
l0,r0 = left, right
while left < right:
while l[left] <= piv and left < right: left += 1
while l[right] > piv: right -= 1
if left < right: l[left], l[right] = l[right], l[left]
l[i_piv], l[right] = l[right], piv
work.append((l0,right-1))
work.append((right+1,r0))

Python is_prime using Miller-Rabin

from random import randrange

def is_prime(n, trials=6):
    """ Miller-Rabin probabilistic prime test.
    """
    if n < 2:
        return False
    i = 0
    while i < trials:
        i+=1
        a = randrange(1, n)
        if pow(a, n-1, n) != 1: # (a**(n-1)) % n
            return False
    return True

# or as a tiny-font-one-liner


def is_prime(n, trials=6):
    return n >= 2 and (trials == 0 or (pow(randrange(1, n), n-1, n) == 1 and is_prime(n, trials - 1)))

uboot pogoplug netconsole

I used this tip to set up my pogoplug to send the uBoot prompt
via udp to my laptop
(see: Use netconsole to troubleshoot uBoot without a serial cable
 http://forum.doozan.com/read.php?3,14,14)

Now, to get the boot prompt from pogoplug (192.168.1.74) to my laptop (192.168.1.72)
I do (on my laptop)

ifconfig en0 alias 192.168.1.72 255.255.255.0

to set an ip alias (remove with -alias), and then

nc -lu 192.168.1.72 6666 & nc -u 192.168.1.74 6666

to communicate with the pogoplug.

Make linux prefer IPv4 connections

Sometimes a DNS name resolves to both an IPv6 and and IPv4 address.  How do you force a program to choose for instance IPv4 over IPv6.

The answer is to change the file /etc/gai.conf which controls the getaddrinfo() (see man gai.conf)

For instance, append

precedence ::ffff:0:0/96  100

at the end of /etc/gai.conf to give high priority to A records.  The filters can also be more specific and made to apply only to specific addresses or subnets.  It doesn't seem to be able to change on a per-process basis with this approach (and of course it requires you to have root privileges to modify /etc/gai.conf).

Thanks to Lmwangi at http://unix.stackexchange.com/questions/9940/convince-apt-get-not-to-use-ipv6-method