VNC to OS X Lion: Gratuitous Passwords and Empty Grey Linen Desktops

 No Responses »
Mar 282012
 

There are two tricks to using VNC from a non Mac to connect to a Mac running OS X Lion.

  1. Turn on the VNC server by enabling System Preferences -> Sharing ->  Screen Sharing. Even though it provides little security, a VNC password must be set so that OS X will present an authentication scheme that makes sense to a standard VNC client. Enable VNC viewers may control screen with password
  2. After connecting, you will see a grey linen-backgrounded desktop with nothing in it. Type your user name and password. After logging in, your desktop contents will display!
 Tagged with: ,

“ERROR: cannot execute UPDATE in a read-only transaction”

 No Responses »
Mar 122012
 

"ERROR: cannot execute UPDATE in a read-only transaction" is what PostgreSQL tells you when you try to execute an update on a replica instead of on the master.

 Tagged with:

Browsing Without Being Tracked

 No Responses »
Mar 102012
 

TL;DR: Install Do Not Track Plus, use Duck Duck Go (with !sp sometimes) for web searches., To go the extra mile also install Straight Google (requires Greasemonkey), Cookie Whitelist and BetterPrivacy.

I don’t like the idea of advertisers, search engines, and social networks building extensive profiles about what I do online (why). A short-list of tools to avoid such tracking:

Prevent Inter-Website Tracking

  • Abine’s Do Not Track Plus is nearly a one-stop shop. I wish more details were available about what it does, but the gist is:
    • Install and maintain a large number of generic do-not-track-me cookies for many ad networks and tracking services. When content is fetched from these sites, the generic cookie is sent rather than one which is unique to you
    • Special handling for social buttons (e.g. Like this on Facebook), in which the button fetched anonymously, but, should you choose to click it, the veil is lifted and the Like associated with your account
    • Many ads are blocked from rendering too, which I hadn’t expected. Those that remain are innocuous enough that I do not use Ad Block Plus any more.

Reduce Google Information Gathering

I store some personal information on Google (thanks to Google+, Google Calendar, etc.). I do not want to Google to associate that personal information with all the web searches I do every day. Do Not Track Plus is of limited value here: if you sign in to Google, Do Not Track Plus will be obliged to permit your identity to be sent. Additional steps are needed:

  • Don’t search with Google. I prefer Duck Duck Go for most searches, thanks to their Zero-click Info and other goodies.
  • For needle-in-the-haystack searches, I find Google often has the best results. Startpage is an anonymous Google Search proxy. Rather than use it directly, I just prefix my Duck Duck Go searches with !sp when needed.
  • Straight Google (requires Greasemonkey) prevents Google’s click-tracking. This is less important if you follow the above steps to avoid doing your web searches at google.com. However, they still track links clicked on their other products, which Straight Google can prevent.

Control Intra-Website Tracking

The above steps should take care of attempts to track your movement across the web. However, most websites will still store long-term cookies in your browser to track your history of interaction with that particular website.

  • Cookie Whitelist is designed to only allow white-listed cookies from being accepted. In practice, this breaks too many websites. For less hassle, configure as follows:
    • Cookie button (the red one): ON. This lets any website set a cookie, but it will be deleted at the end of the session
    • For the few websites you wish to remain logged in to (or otherwise personalized) click the green button to whitelist as needed
    • Do not accept third-party cookies
  • BetterPrivacy is to Flash LSOs (local shared objects, or Flash cookies) what Cookie Whitelist is to regular cookies. Alas with a more confusing set of configuration options.

Note: this post is (obviously?) not about how to avoid your employer/ISP/government monitoring what you do online. To hide what you are doing from someone who has access to all your traffic, you need encryption and proxying. A good first stop to get some encryption is EFF’s HTTPS Everywhere. This goes a long way to prevent the person nearby in the coffee shop from stealing your Facebook account.

Originally published 2012-03-10. Updated 2012-03-14 with intra-website tracking steps.

 Tagged with: , , , , , , ,

Google’s Click Tracking and How to Disable It

 No Responses »
Mar 102012
 

By default, Google tracks every search result you click on. They do this surreptitiously: URLs in Google search results appear to go directly to the destination:

 

But, upon click, URLs in Google search results change to go to Google first!

 

Straight Google removes this tracking from Google URLs across all Google products. Easy to install and no configuration needed, but you must install Greasemonkey first.

 Tagged with: , , ,

Fixing key-repeat in OS X Lion (and restoring sanity for Vim keybindings) on a per-application basis

 1 Response »
Mar 022012
 

Starting with OS X Lion, holding down a key will bring up a menu of alternate characters rather than repeating the key. (This is a feature). There are many tips on how to re-enable key-repeat globally. But you can also control the behavior per-application (thanks, Egor Ushakov). This is handy for e.g. IntelliJ or RubyMine, or any other app that provides Vim-style keyboard bindings. The magic commands are:

% defaults write com.jetbrains.intellij ApplePressAndHoldEnabled -bool false
% defaults write com.jetbrains.rubymine ApplePressAndHoldEnabled -bool false

But how do you figure out what the magic identifier for your application is? Simple: defaults domains will list them all:

defaults domains | gsed -e 's/, /\n/g' | grep jetbrains
com.jetbrains.intellij
com.jetbrains.intellij.ce
com.jetbrains.rubymine
jetbrains.communicator.core

Note that in order to munge the commas into newlines for grep, gsed was required because OS X default sed cannot (easily) insert newlines.

 Tagged with: , ,

Inserting newlines with sed on OS X

 No Responses »
Mar 022012
 

Out of the box, inserting newlines does not work with sed on OS X:

% echo foo,bar,baz | sed -e 's/,/\n/g'
foonbarnbaz

The simple solution is to use GNU sed, which is already installed (as gsed), instead of the default BSD version:

% echo foo,bar,baz | gsed -e 's/,/\n/g'
foo
bar
baz

Alternatively, it is possible (though fiddly) to trick BSD sed into inserting newlines using extquotes.

 Tagged with: , ,

Random file selections with Python

 No Responses »
Feb 212012
 

After my previous adventures in slicing and dicing a huge XML file, I wanted a means to randomly select files. But first, the directory had so many entries it was unwieldy on my laptop. The Python script below divvies the files up into directories of up to 1000 files each. (Adaptable to other contexts via slight tweaking of the filename regex and subdir name generation.)

#!/usr/bin/python
import os
import re
where = '.' # source directory 

ls = os.listdir(where)
for f in ls:
  m = re.search('.*_COMM-([0-9]+).xml', f)
  if m:
    subdir = "%03d" % (int(m.group(1)) / 1000)
    try:
      os.mkdir(subdir)
    except OSError as e:
      pass
    os.rename(f, os.path.join(subdir, f))

Now on to the random selection, again with Python:

#!/usr/bin/python
import os
import random
import re
import sys

if len(sys.argv) > 1:
  where = sys.argv[1]
else:
  where = '.' # source directory 

subdirs = filter(lambda x: re.search('^[0-9]*$', x), os.listdir(where))
subdir = os.path.join(where,random.choice(subdirs))
print os.path.join(subdir,random.choice(os.listdir(subdir)))

A quick shell loop leverages the Python script to grab files and dump into a repository of test data. Works on ZSH, Bash, perhaps others:

for i in {1..250}; do cp $(./pick_a_file.py sub_dir_with_files) /destination/dir/filename_prefix_$(printf "%03d" $i).xml; done;

 

 

 Tagged with: , , ,

Thunderbird still displays expunged IMAP messages

 3 Responses »
Feb 142012
 

There is lots to be said about the intricacies of IMAP delete flags vs. actual expunging of deleted messages and the confusion caused when something is merely flagged for deletion and the user expected it to be really gone. This post is not about that. Everyone agrees that once a message is expunged, it definitely should be gone. But sometimes expunged messages still display in Thunderbird!

I often observe this:

  1. Delete message on the way to work using K-9 on my phone.
  2. Arrive at work and message is gone from my Inbox in Mail.app
  3. Come home, download new mail in Thunderbird and see an Inbox full of undead messages.

No amount of re-expunging and re-fetching mail helps. Grepping through the server-side Maildir shows the messages really are gone from the folders in which Thunderbird is still showing them.

It turns out the reason they are still displaying in Thunderbird is mundane client-side index corruption. To clean things up:

  1. Right-click on mailbox
  2. Choose Properties...
  3. Click Repair Folder
  4. Rejoice at tidy mailbox
 Tagged with: , ,

How to treat a bare value as an Array in Ruby

 No Responses »
Feb 082012
 

Often Array(arg) is used for this, but is flawed. Note the last result when applied to a Hash:

> Array(42)
 => [42]
> Array([1,2,3])
 => [1, 2, 3]
> Array(nil)
 => []
> Array("foo")
 => ["foo"]
> Array({"foo" => "bar", "biz" => "baz"})
 => [["foo", "bar"], ["biz", "baz"]]

What went wrong is that Array() calls the (now deprecated) to_a on each of its arguments. Hash has a custom to_a implementation with different semantics. Instead, do  this:

class Array
  def self.wrap(args)
    return [] unless args
    args.is_a?(Array) ? args : [args]
  end
end

That yields the expected results, even for Hashes:

> Array.wrap(42)
 => [42]
> Array.wrap([1,2,3])
 => [1, 2, 3]
> Array.wrap(nil)
 => []
> Array.wrap("foo")
 => ["foo"]
> Array.wrap({"foo" => "bar", "biz" => "baz"})
 => [{"foo"=>"bar", "biz"=>"baz"}]

Use of is_a? is deliberate; duck-typing in this situation ([:[], :each].all? { |m| args.respond_to? m }) yields unexpected surprises since e.g. String is Enumerable and would not get wrapped.

For further discussion see Ruby-forum thread “shortcut for x = [x] unless x.is_a?(Array)” and StackOverflow “Ruby: Object.to_a replacement“.

 Tagged with:

Splitting large XML files with xml_split and sed (preserving root element and namespace declaration)

 No Responses »
Feb 082012
 

Slicing up XML files is best done with an XML parser. (Regular expressions, csplit, etc. are too easily confused by arbitrary strings in CDATA sections.) xml_split (may be obtained with CPAN by installing XML::Twig) mostly does the trick. Given a file like:

<?xml version="1.0" encoding="UTF-8"?>
<foo:Root xmlns:foo="http://www.foo.bar/fnarf/foo">
  <foo:child>
    ...
  </foo:child>
  <foo:child>
    ...
  </foo:child>
</foo:Root>

…xml_split can create many files, each containing:

<?xml version="1.0" encoding="UTF-8"?>
<foo:child>
  ...
</foo:child>

However, this loses the namespace declaration and the enclosing root element. Luckily, a little sed magic can bring those back:

find . -name '*.xml' | xargs -n1 sed -e '1 a\
<foo:Root xmlns:foo="http://www.foo.bar/fnarf/foo">
' -e '$ a\
</foo:Root>
' -i ''

find lists all the files, xargs invokes sed on them one by one (-n1), and sed adds the opening tag with namespace declaration after the first line (1 a) and the closing tag after the last line ($ a). Now each file looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<foo:Root xmlns:foo="http://www.foo.bar/fnarf/foo">
  <foo:child>
    ...
  </foo:child>
</foo:Root>
 Tagged with: ,
 Older Entries
lankycoder blog © 2011-2012 by Lorrin Nelson Creative Commons License Blog content under CC BY-SA License. Code excerpts from larger projects may be available under more permissive license; see the project. Suffusion theme by Sayontan Sinha