blog.layer2.org

If you didn’t know already, there is a new version of Rails out there.

And I’m not referring to the Rails 2.0 preview. This is Rails 1.2.5, which contains fixes for a JSON XSS (cross-site scripting) vulnerability. I’m not horribly familiar with the details, but the site does say that you don’t have to worry about it if you’re not using JSON. Probably a good idea to upgrade anyway.

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I’ve been perusing through my logs lately and found the user agent “radianrss-1.0″ numerous times. I’d never heard of this program (maybe an RSS reader?), so I did a google search. The only commentary I found was this post speculating that 142.166.3.123 was possibly involved in the compromise of katester.net.

Interestingly enough, the rest of the search results are the traffic statistics pages of various Wordpress blogs around the Internet. There doesn’t seem to be a clear answer for what “radianrss” is, or why 142.166.3.122-123 is constantly indexing all of my blog posts.

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==========================================================

 ____  ___    __        ______ _____         ____  _____
 | _ \| _ \   \ \      / /  _ \_   _| __   _|___ \|___ /
 || | || ||____\ \ /\ / /| |_) || |   \ \ / / __) | |_ \
 ||_| ||_||_____\ V  V / |  _ < | |    \ V / / __/ ___) |
 |___/|___/      \_/\_/  |_| \_\|_|     \_/ |_____|____/ 

                       DD-WRT v23 SP2

http://www.dd-wrt.com

==========================================================

I installed dd-wrt on my Linksys WRT54g because I was having problems with the Sveasoft Alchemy firmware. The wireless was dropping constantly, which can be real annoying when you’re trying to do a video call on Skype. My suspicion was that the firmware image was too large and too many services were trying to be run at once, and the unit was running out of memory.

Once long ago I had problems with the Alchemy firmware getting an IP address from my DSL connection. I managed to get syslog working (shouldn’t have been hard, but it didn’t work well with Alchemy) and the errors seemed to point to the fact that the unit was running out of memory. It would eventually work, it just took 20 minutes to get an IP address after it booted. Then it would stay up for months.

I guess I’ve just been out of the loop with regard to the newer firmwares. dd-wrt has much of the same basic functionality in their ‘mini’ version as the Sveasoft Alchemy fully featured version did. And to think that at point I paid for Alchemy because I wanted a more featureful, stable firmware

The wireless issues have gone away, and the web interface has a much more polished feel to it. I like logging into the router just to look at the interface and see the random stats. It also gives you status on the signal strength of the wireless clients, which can be very useful!

The dd-wrt firmware is famous for being able to do client mode bridging, i.e. act as a transparent wired-to-wireless bridge. I’m looking forward to trying that out some day.

By the way, although my unit will broadcast at a power of 251mW, I read on the dd-wrt wiki that 84mW is ideal for most hardware in terms of getting the best signal-to-noise ratio. At 84mW, I get a SNR of somewhere between 30-40, so I feel like that is probably pretty accurate information, considering I probably only need a SNR of 10-15 to get a very good wireless signal.

Try out dd-wrt today!

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There are two major reasons (I know of) that can cause extremely slow SSH logins – anywhere in the range of 15-30 seconds. It doesn’t seem like a long time, but it takes forever to wait that out sitting at the terminal.

Say no to GSSAPIAuthentication

For some reason, GSSAPIAuthentication is turned on by default in Ubuntu Feisty (7.04). If you ssh -v somewhere.com, you’ll see this in the output:

...
debug1: Local version string SSH-2.0-OpenSSH_4.3p2 Debian-8ubuntu1
debug1: An invalid name was supplied
Cannot determine realm for numeric host address

debug1: An invalid name was supplied
A parameter was malformed
Validation error

debug1: An invalid name was supplied
Cannot determine realm for numeric host address

debug1: An invalid name was supplied
A parameter was malformed
Validation error

debug1: SSH2_MSG_KEXINIT sent
...

There are two ways to fix it. You can edit either /etc/ssh/ssh_config to include

GSSAPIAuthentication no

Or, you can edit ~/.ssh/config and add the same line. The only difference is that /etc/ssh/ssh_config will affect all systems users – probably a good thing.

Slow/broken DNS lookups

Each time you log into an OpenSSH server, it will typically perform a reverse-lookup on your IP address and store it in wtmp (try running the command “last”). If that DNS lookup times out, you’ll be in for a big delay. Whats worse, OpenSSH has a habit of performing the lookup 3 or 4 times, further extending the delay to 30 seconds or more.

Its generally best to fix the source of the problem by fixing whatever problem exists in your DNS infrastructure. This could be as simple as pointing /etc/resolv.conf to the correct nameserver.

If you’re really in a bind, you can pass the -u0 flag to sshd. Unfortunately, the sshd man page does not reveal any config file options to accomplish the same thing. But, the -u0 flag will stop sshd from performing any lookups that are not absolutely necessary as part of the authentication mechanism.

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If you want to share a PDF of a web page or any other document with another person, PDF is usually the way to go. There are free PDF printers out there for Windows, but fortunately the necessary software is probably already installed on your Linux distribution. Just use ps2pdf.

First, print from your application (ie. Firefox) and make sure to check “Print to file”:

Press Print, save the file as filename.ps , and then run the following command:

$ ps2pdf filename.ps

The resulting file will be filename.pdf.

This is also a good way to convert old PS files (which can get pretty large) to the smaller PDF format. And, if for some reason you want to go the other direction, you can always use the pdf2ps utility.

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While I recently found out about Ruby’s ‘methods’ method, I also found that Rails’ “ruby script/console” will do tab completion:

>> a = Array.new
=> []
>> a.
Display all 157 possibilities? (y or n)
a.fetch                              a.method                             a.slice
a.__id__                             a.fill                               a.methods                            a.slice!
a.__send__                           a.find                               a.min                                a.sort
a.all?                               a.find_all                           a.nil?                               a.sort!
a.any?                               a.first                              a.nitems                             a.sort_by
a.assoc                              a.flatten                            a.object_id                          a.split
a.at                                 a.flatten!                           a.pack                               a.subclasses_of
a.b64encode                          a.freeze                             a.partition                          a.sum
a.blank?                             a.frozen?                            a.pop                                a.suppress
a.class                              a.gem                                a.pretty_inspect                     a.taguri
a.clear                              a.grep                               a.pretty_print                       a.taguri=
a.clone                              a.group_by                           a.pretty_print_cycle                 a.taint
a.collect                            a.hash                               a.pretty_print_inspect               a.tainted?
a.collect!                           a.id                                 a.pretty_print_instance_variables    a.to_a
a.compact                            a.in_groups_of                       a.private_methods                    a.to_ary
a.compact!                           a.include?                           a.protected_methods                  a.to_default_s
a.concat                             a.index                              a.public_methods                     a.to_formatted_s
a.copy_instance_variables_from       a.index_by                           a.push                               a.to_json
a.daemonize                          a.indexes                            a.rassoc                             a.to_param
a.dclone                             a.indices                            a.reject                             a.to_s
a.decode64                           a.inject                             a.reject!                            a.to_sentence
a.decode_b                           a.insert                             a.remove_subclasses_of               a.to_set
a.delete                             a.inspect                            a.replace                            a.to_xml
a.delete_at                          a.instance_eval                      a.require                            a.to_yaml
a.delete_if                          a.instance_exec                      a.require_gem                        a.to_yaml_properties
a.detect                             a.instance_of?                       a.require_library_or_gem             a.to_yaml_style
a.display                            a.instance_values                    a.respond_to?                        a.transpose
a.dup                                a.instance_variable_get              a.returning                          a.type
a.each                               a.instance_variable_set              a.reverse                            a.uniq
a.each_index                         a.instance_variables                 a.reverse!                           a.uniq!
a.each_with_index                    a.is_a?                              a.reverse_each                       a.unloadable
a.empty?                             a.join                               a.rindex                             a.unshift
a.enable_warnings                    a.kind_of?                           a.select                             a.untaint
a.encode64                           a.last                               a.send                               a.values_at
a.entries                            a.length                             a.shift                              a.with_options
a.eql?                               a.load                               a.silence_stderr                     a.yaml_initialize
a.equal?                             a.map                                a.silence_stream                     a.zip
a.extend                             a.map!                               a.silence_warnings
a.extend_with_included_modules_from  a.max                                a.singleton_methods
a.extended_by                        a.member?                            a.size

Unfortunately the same thing doesn’t work for the irb. Of course you can always

a.methods.sort

to see the same information.

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So there are plenty of resources out there to learn how to use has_many :through associations.

I followed them over and over again but couldn’t get my code to work. I knew I had the basic structure setup correctly, since the examples are pretty straightforward, and the concept is not difficult. My has_and_belongs_to_many code originally looked like this:

class Soda < ActiveRecord::Base
  has_and_belongs_to_many :distributors
end
 
class Distributor < ActiveRecord::Base
  has_and_belongs_to_many :sodas
end

Of course there was also a many-to-many join table migration:

class DistributorsSodasJoinTable < ActiveRecord::Migration
  def self.up
    create_table :distributors_sodas, :id => false do |t|
      t.column :soda_id, :int
      t.column :distributor_id, :int
    end
  end  
 
  def self.down
    drop_table :distributors_sodas
  end
end

This works quite nicely:

>> Soda.find(1).distributors
=> []

Later found that I needed to add attributes in the join table to associate extra fields on the Distributors <-> Sodas relationship. has_and_belongs_to_many does not have a Rails way to access those extra fields in the join table. I’ve successfully done it through SQL, but much guilt and remorse lead me to finally learn has_many :through.

This was my best initial attempt:

class Soda < ActiveRecord::Base
  has_many :distributors_sodas
  has_many :distributors, :through =>; :distributors_sodas
end
 
class Distributor < ActiveRecord::Base
  has_many :distributors_sodas
  has_many :distributors, :through => :distributors_sodas
end
 
class DistributorsSodas < ActiveRecord::Base
  belongs_to :soda
  belongs_to :distributor
end

All goes well until I try to do a quick test:

>> Soda.find(1).distributors
NameError: uninitialized constant Soda::DistributorsSoda
...
        from (irb):4

Umm… what? I never tried to instantiate an object of the type Soda::DistributorsSoda. Instead, I was simply trying to use the DistributorsSodas ActiveRecord object, right?

It turns out that has_many :through (apparently) can’t handle using the join tables created by has_and_belongs_to_many. Its just a naming issue – has_many :through will work fine using a one-to-many join table like distributor_sodas (note the missing ’s’ on distributor). If you need a many-to-many join, you have to rename the table to fix the (pluralization?) problem. I deleted the DistributorsSodas model and created the Store model.

class Soda < ActiveRecord::Base
  has_many :stores
  has_many :distributors, :through => :stores
end
 
class Distributor < ActiveRecord::Base
  has_many :stores
  has_many :sodas, :through => :stores
end
 
class Store < ActiveRecord::Base
  belongs_to :soda
  belongs_to :distributor
end

This proved a much better result:

>> Soda.find(1).distributors
=> []

In the end, the association naming convention actually make more sense. I was bummed to have to change the table/model names though.

Please comment if you know how to create the association without changing the model name.

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Its long been known that you can use something like the User Agent Switcher to make it appear like you’re using a different operating system than you really are. This can be useful on some websites that insist you need to run Windows – when in fact Linux or practically any other operating system will work fine.

But for those sites that are actually telling the truth, you can often run Firefox under WINE with very good results. Just head over to www.getfirefox.com and download the Windows binary. The site actually does its own OS detection, so you’ll probably want to choose “Other Systems and Languages.” Once you have it, make sure you have WINE installed. I also installed the MS truetype fonts because it looks terrible otherwise.

# apt-get install wine msttcorefonts

And then start the installer

$ wine Firefox\ Setup\ 2.0.0.7.exe

You’ll go through the normal install process, and when you’re finished you’ll see a new Firefox icon on your Linux desktop:

Double-click it and you should be good to go! If you want to visit a site with audio, you’ll want to run winecfg, visit the Audio tab, choose your settings (I just left the defaults) and click Apply. Otherwise you might run into some issues with Firefox crashing. If its any consolation, Firefox will crash on certain sites powered by Move Networks in Windows, too, if there is no audio driver installed. This is probably related to the Firefox extension you must install to view the site.

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I recently wrote about the cron job that I run to keep my Debian and Debian-like servers up to date automatically.

It turns out that apt-get (or libapt, more specifically) has a mechanism to automatically download and install security updates. This will work across package management applications (apt-get, synaptic, aptitude, etc) and is very simple to setup. Edit /etc/apt/apt.conf.d/10periodic to include the following:

APT::Periodic::Update-Package-Lists "1";
APT::Periodic::Download-Upgradeable-Packages "1";
APT::Periodic::AutocleanInterval "0";
APT::Periodic::Unattended-Upgrade "1";

Your distribution should already have a cron job (usually in /etc/cron.daily/apt) that runs every day and updates as per these configuration options. To see the entire config, run

$ apt-config dump

For those interested, this configuration setting is what Synaptic sets when using its “Install security updates without confirmation” option.

Thanks to g for pointing this out.

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If you didn’t already know, Ubuntu 7.10 Gutsy Gibbon will be coming soon!

Maybe I’ll finally get suspend support for my dual core Dell XPS desktop?

Any guesses if the Ruby and Rails packaging will be any better?

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