A little one-liner: rename to lowercase recursively

Here is my little one-liner, because I used it today and I find it fun:

for f in `find .` ; do mv $f `echo $f | tr '[A-Z]' '[a-z]'` ; done 

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netcat as a logging tcp proxy

I felt I needed to write an article about netcat, so here is it !
Netcat is an incredibly usefull tool, that allows you to play with tcp connection easily from the shell.
Basically, as it name implies, it’s just cat over the network, but what its name doesn’t tell you is that it also can act as a socket listener.
So let’s play with pipes, here is one of my favourite use of netcat:

mkfifo proxypipe
cat proxypipe | nc -l -p 80 | tee -a inflow | nc localhost 81 | tee -a outflow 1>proxypipe

This command will redirect traffic from localhost:80 to localhost:81, in the inflow file you while find the incoming http request, in the outfile, you will find the http response from the server.
Similarly, you can do this:

cat proxypipe | nc -l 80 | tee -a inflow | sed 's/^Host.*/Host: www.google.fr/' |  nc www.google.fr 80 | tee -a outflow >proxypipe

This will allow your browser to point to google using http://localhost .
Anyway, this is my favourite but netcat has thounds of other uses, have a look at it !
It can be usefull for file transfers (gzip|nc) , performance measurement (dd|gzip), protocol debugging (replaying requests), security testing (nc does port scan) …

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ubuntu and bind acting as slave

While installing a slave dns server with bind, I went into trouble. I could not understand why my slave zone would not synchronize. Actually I found these entries in /var/log/daemon.log:

named[24309]: dumping master file: /etc/bind/tmp-b0KyuKU5pG: open: permission denied
named[24309]: transfer of 'domain.com/IN' from w.x.y.z#53: failed while receiving responses: permission denied

It appears that since hardy, ubuntu doesn’t allow the named process to write in /etc/bind/ while it’s running.
Ubuntu is configured to allow slave zone to stay in /var/cache/bind/db.domain.com

So your slave zone will look like:

zone "domain.com" IN {
        type slave;
        file "/var/cache/bind/db.domain.com";
        masters { w.x.y.z; };

For the details, it’s due to apparmor, and precisely the file /etc/apparmor.d/usr.sbin.named.
As shipped with ubuntu, this file contains the authorizations for the named process that restricts where bind can write its zones, and reserves /var/cache/bind/ as the directory where bind is supposed to put its slave zones.
This seems to me technically good because /etc is pretty much supposed to be “read-only able” (beside /etc/mtab and /etc/resolv.conf that you can put in /dev/shm or link from /var/etc). This makes me wonder where to put master zones that you want to change ? Probably in /var/lib/bind because it’s where dynamically updated zone are.

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Installing redmine 0.8 on intrepid (ubuntu 8.10)

I’ve successfully insalled redmine pretty much easily but I needed to find out what packages to install with apt, which one with gem, which version …
Here is my magic receipe to install it all:

apt-get update 
apt-get install subversion mysql-server rubygems rake pwgen
# next line generates a password for the database
export PASSWORD=`pwgen -nc 8 1`
gem install -v=2.1.2 rails
cd /opt/
svn export http://redmine.rubyforge.org/svn/branches/0.8-stable redmine-0.8
cd redmine-0.8/
cat <<EOF >> config/database.yml
  adapter: mysql
  socket: /var/run/mysqld/mysqld.sock 
  database: redmine
  host: localhost
  username: redmine
  password: $PASSWORD
  encoding: utf8

rake db:migrate RAILS_ENV="production"
rake redmine:load_default_data RAILS_ENV="production"
apt-get remove pwgen subversion
RAILS_ENV="production" ./script/server  

And that’s it ! Redmine is running on port 3000.
I did this on an EC2 instance and it works like a charm (ami-7cfd1a15).
Maybe next article will discuss running redmine in mongrel or apache, and creating an init script for having redmine running on boot !

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HTTP’s 301 and 302

Just a little note, 301 is the HTTP code for “temporarly moved”, 302 is “permanently moved”.
Seems 302 is genereally more usefull and works better.
From what I noticed (I’m not sure about it), 302 has better SEO. Also some browsers seems to make better cache use with 302 and generating less requests on your webserver.

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Hostname and underscore

RFC 952 and RFC 1123 explains the rules for choosing a hostname. I noticed recently that a lot of admins (including me) are using underscores in hostnames, but this doesn’t follow RFCs. This can lead to strange behaviours, such as mail not delivered with an RFC compliant mail server to an MX that have underscores in its name …
I noticed that because the “hostname” command on linux can set the hostname of a system, but the command doesn’t accept underscores. So guys, don’t use underscores !

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MySQL “pretty printing”

I just discovered an apparently wide spread tip for mysql:

mysql> select 1, 2, 3, 4 ;
| 1 | 2 | 3 | 4 |
| 1 | 2 | 3 | 4 |
1 row in set (0.00 sec)

mysql> select 1, 2, 3, 4 \G;
*************************** 1. row ***************************
1: 1
2: 2
3: 3
4: 4
1 row in set (0.00 sec)

As you might have seen, the difference comes from the “\G” !

It’s very usefull when you select lot of columns that doesn’t fit the width of your terminal !
Shame on me I didn’t knew that before !

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