druzn3k

Arel Cheatsheet on Steroids

A (more) complete cheatsheet for Arel, including NamedFunction functions, raw SQL and window functions.

Tables

posts = Arel::Table.new(:posts)
posts = Post.arel_table # ActiveRecord

Table alias

druzn3k

//CC2018
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druzn3k

#!/bin/sh​
# Build Zsh from sources on Ubuntu.
# From http://zsh.sourceforge.net/Arc/git.html and sources INSTALL file.

# Some packages may be missing
sudo apt-get install -y git-core gcc make autoconf yodl libncursesw5-dev texinfo

git clone git://zsh.git.sf.net/gitroot/zsh/zsh

cd zsh

druzn3k

libnfc supports UUID writable cards and even has some dedicated tools for them.

However it doesn't work with some of the cards found on eBay that are even simpler to use. Sector 0 is unlocked and can be written without any additional commands. libnfc requires a small patch to get it working.

Following has been tested under ArchLinux with modified libnfc 1.5.1, mfoc 0.10.2 and a SCL3711 dongle.

Patch & recompile libnfc

The patch is fairly simple, open libnfc-1.5.1/utils/nfc-mfclassic.c and comment 2 lines (it was lines 384 and 385 for me):

// Try to write the trailer

druzn3k

Trashing the Vodafone Station

How to replace the Vodafone Station with your very own router

Vodafone forces its customers to use their modem/router, the "Vodafone Station": using any other router is impossible because authentication is being done via a custom PPPoE setup.
In the PPPoE packet there is a field named Host-Uniq which is used to separate packets from different PPPoE sessions: Vodafone requires the Station serial number to be put in this field as authentication.

Hardware setup

A Linux router with root access is needed to replace the Station with. With an xDSL connection a modem with a custom firmware like OpenWrt has to be used, most likely one based on a Lantiq SoC.
For a FTTH internet connection then every machine with at least two gigabit ethernet interface and a decent CPU will do it.

druzn3k

# Colors
end="\033[0m"
black="\033[0;30m"
blackb="\033[1;30m"
white="\033[0;37m"
whiteb="\033[1;37m"
red="\033[0;31m"
redb="\033[1;31m"
green="\033[0;32m"
greenb="\033[1;32m"

druzn3k

-- show running queries (pre 9.2)
SELECT procpid, age(clock_timestamp(), query_start), usename, current_query 
FROM pg_stat_activity 
WHERE current_query != '<IDLE>' AND current_query NOT ILIKE '%pg_stat_activity%' 
ORDER BY query_start desc;

-- show running queries (9.2)
SELECT pid, age(clock_timestamp(), query_start), usename, query 
FROM pg_stat_activity 
WHERE query != '<IDLE>' AND query NOT ILIKE '%pg_stat_activity%' 

druzn3k

Monte-Carlo Permutation Testing

Near the end of my first statistics class, I was introduced to the concept of a hypothesis test: given two sample sets, determine the probability that they were drawn from the same population. If this is less than your desired p-value (typically 5% or less, depending on your field), you can reject the [null-hypothesis][1] and accept the alternative hypothesis that the two samples are indeed from different populations.

This was presented to me in the context of social sciences, but it comes up in

druzn3k

# maximum capability of system
user@ubuntu:~$ cat /proc/sys/fs/file-max
708444

# available limit
user@ubuntu:~$ ulimit -n
1024

# To increase the available limit to say 200000
user@ubuntu:~$ sudo vim /etc/sysctl.conf

druzn3k

What I actually did

/etc/security/limits.conf

elasticsearch hard memlock 100000

/etc/default/elasticsearch