I had a very frequent cronjob that in rare cases could be relatively slow. To avoid multiple instances of this cronjob running in parallel, I decided to use flock to ensure that only one instance could run at a time.

flock works by acquiring a lock to a file, and if it can do so running a command. In order not to wait but simply give up when the file is locked, you can add -n:

flock /tmp/my.task.lock -n -c "bin/my-long-running-job"

Using whenever, and since this was a rake task, the follo...

MutationObserver provides developers a way to react to changes in a DOM. Any: insertion, deletion, attribute change – anything.

Quickstart: https://davidwalsh.name/mutationobserver-api

Relevant caniuse.com search: http://caniuse.com/#feat=mutationobserver

Command line text editor with syntax highlighting, menus (F1), etc.

This might be a worthy replacement for nano if you don't want to use vim.

From time to time, RubyMine suddenly did not accept any keyboard input and felt crashed, while mouse interaction was still possible. This apparently happens to all IntelliJ IDEs, especially on Ubuntu 14.04.

I've managed to fix it by having a shell script that exports XMODIFIERS="" when launching RubyMine, like this:

#!/bin/sh
XMODIFIERS= /home/arne/rubymine/bin/rubymine.sh

It has been working reliably for me ever since, at least until RubyMine 8.

An alternate solution suggested on the [Jetbrains issue tracker](https://youtrack....

Web safe fonts are fonts that are pre-installed by many operating systems. While not all systems have the same fonts installed, you can use a web safe font stack to choose several fonts that look similar, and are installed on the various systems that you want to support. If you want to use fonts other than ones pre-installed, as of CSS3, you can use Web Fonts.

If you need to install any of the widely-supported fonts listed there, you'll probably find them at www.fontpalace.com.

Table of contents of the linked article:

What are Web Fonts?

• Advantages of Web Fonts
• Disadvantages of Web Fonts
  • Fallback Fonts
  • CSS3 @font Declaration Example
  • Fallback Font Example
  • Render Blocking and Critical Rendering Path
  • FOIT

Optimizing Web Font Delivery Further

• Prioritize Based On Browser Support
• Choose Only Styles You Need
• Character Sets
• Host Fonts Locally or Prefetch
• Store in LocalStorage with Base64 Encoding
• Another Method

Web Font Pe...

A JS library that allows you to embed an iframe that automatically shrinks or expands to match its content.

(Untried.)

You can configure a stat socket for haproxy in the global section of the configuration file:

global
  daemon
  maxconn 999
  user foobar
  stats socket /var/run/haproxy.stat  # this is the line you want to configure

You need socat to query data from this socket.

After installing socat and reconfiguring haproxy you can use this socket to query data from it:

• show informations like haproxy version, PID, current connections, session rates, tasks, etc..

  echo "show info" | socat unix-connect:/var/run/haproxy.stat stdio
  

...

After restarting an OpenStack host you may encouter problems with missing iptables rules (we're on an quite old release of OpenStack currently. Maybe this is fixed in newer releases). The nova chains appear in the iptables -L output but they're empty. NAT is working fine. The reason is, that the NAT chains are configured by nova-network while the filter rules are managed by nova-compute. I didn't manage to find the cause of this behaivour yet, but I think it has something to do with the start order of the nova services. (When `nova-net...

Use this snippet by Achu from Ask Ubuntu:

ping hostname.tld | while read pong; do echo "$(date): $pong"; done

This gives you lines like:

Wed Nov  4 10:32:31 CET 2015: 64 bytes from 1.2.3.4: icmp_seq=298 ttl=61 time=0.673 ms
Wed Nov  4 10:32:32 CET 2015: 64 bytes from 1.2.3.4: icmp_seq=299 ttl=61 time=0.616 ms
Wed Nov  4 10:32:33 CET 2015: 64 bytes from 1.2.3.4: icmp_seq=300 ttl=61 time=1.04 ms

When you're developing a gem, never list the same dependency as both runtime and development dependency in your .gemspec.

So don't do this:

spec.add_dependency 'activesupport'
spec.add_development_dependency 'activesupport', '~> 2.3'

If you do this, your gemspec will not validate and modern versions of Bundler will silently ignore it. This leads to errors like:

Could not find your-gem-0.1.2 in any of the sources

What to do instead

If you want to freeze a different version of a dependency for your t...

While you can use Apache as a reverse proxy, it tries to be too smart. Try nginx instead, it's much simpler to set up.

After struggling with Apache for quite a while, since I simply could not make it pass through the Digest Authentication of my target host (that I proxied to), I switched to nginx. Here is what I did.

1. Have nginx

   sudo apt-get install nginx
   

2. Define your nginx config, e.g. at /etc/nginx/conf.d/reverse-proxy.conf:

   server {
     listen 127.0.0.1;
     
     location /...
   

There are many solutions, but a very concise one is this:

hash.merge!(hash) do |key, old_value, new_value|
  # Return something
end

The block of merge! will be called whenever a key in the argument hash already exists in the base hash. Since hash is updated with itself, each key will conflict and thus allow you to modify the value of each key to whatever you like (by returning old_value you'd get the behavior of Rails' reverse_merge!, by re...

A list of common computer I/O actions and how long they take.

Visual comparison chart: http://i.imgur.com/k0t1e.png

One useful postgres command I stumbled upon recently was \x. It gives you an expanded display which allows you to actually read the results of your select * from queries. The link below describes a few more useful techniques and commands.

While you usually do not need a Content-Type on GET request (which have a blank body), an external API may still force you to send one.
Angular's $http service will strip that header when the request data (body) is blank. [1] This is possibly a misconception of RFC2616.

Here is how to send GET requests with a Content-Type header in Angular.

Example

Consider this request:

$http({ me...

Now that CarrierWave is no longer maintained, Shrine might be worth a look.

Nobody needs HTML e-mails. However, you occasionally might have to write an HTML message for some weird reason. Here is how:

1. Hold the Shift-Key while clicking on "Write", "Reply", "Reply All", or "Forward".

That's it. :)

A great walkthrough through several design iteration of the same landing page.

Rubygems can produce lots of deprecation warnings, but sometimes, you cannot fix them. To have a tidy terminal with output that matters, add this to the top of your Gemfile and enjoy silence:

Deprecate.skip = true if defined?(Deprecate.skip)
Gem::Deprecate.skip = true if defined?(Gem::Deprecate.skip)

# all gems go here ...

(Inspiration)

Sometimes you want to know exactly how many objects exist within your running Ruby process. Here is how:

stats = {}
ObjectSpace.each_object  {|o| stats[o.class].nil? ? stats[o.class] = 0 : stats[o.class] += 1 }; stats

=> {String=>192038, Array=>67690, Time=>2667, Gem::Specification=>2665, Regexp=>491, Gem::Requirement=>16323, Gem::StubSpecification=>2665, ...}

Maybe you want to sort it like this:

stats.sort_by {|k,v| v }

You can configure RSpec 3.3+ to raise an error when attempting to stub or mock a non-existing method. We strongly recommend to do this as non-verified stubs are a footgun.

You can enable this behavior by adding the following to your spec_helper.rb:

RSpec.configure do |config|
  config.mock_with :rspec do |mocks|
    mocks.verify_partial_doubles = true
  end
end

This will also replace stub_existing from our rspec_candy.

This is basically Ruby-native syntax for andand.