If you need to run a program on a remote machine (e.g. to your office PC) with a graphical UI (and you trust the remote machine), you can use SSH X-Forwarding. I sometimes use this to connect to a virtual machine installed on my work PC from my home office.

Forwarding X over SSH

To use X forwarding, when connecting to the remote machine, and add -X to the ssh call. Now, when you start a program with a UI (e.g. virtualbox) in that SSH session, a window will open on your local machine. It will not be particularly ...

Migrating data from a legacy into a new system can be a surprisingly large undertaking. We have done this a few times. While there are significant differences from project to project, we do have a list of general suggestions.

Before you start, talk to someone who has done it before, and read the following hints:

Understand the old system

Before any technical considerations, you need to understand the old system as best as possible. If feasible, do not only look at its API, or database, or frontend, but let a user of the old system sho...

In general, the tracker should always be the definitive source of truth of what needs to be done as part of a project. If you identify a task that needs to be done, you should create a story. If you learn something that contradicts an existing story, change it.

The tracker can contain two types of stories: Developer stories, and non-developer stories.

Non-developer stories

Non-developer stories should be clearly marked. They usually belong to the PM (or maybe people from the operations team). Those story can take all forms, could just...

Google Chrome has a subtle rendering bug that hits me once in a while. It usually occurs in sliders with HTML content.

The issue

When a slider contains a composited[1] element, the element will overlap any other element when sliding, being rendered as frontmost element. After the slider has settled, stacking order jumps back to normal.

It seems like Chrome is doing its compositing wrong. This doesn't happen in Firefox.

The cause

The issue only occurs if:

• two elements A and B are nested inside an element C
• A overlaps B (part...

Having a unique selector for an element is useful to later select it from JavaScript or to update a fragment with an Unpoly.

Haml lets you use square brackets ([]) to generate a unique class name and ID from a given Ruby object. Haml will infer a class attribute from the given object's Ruby class. It will also infer an id attribute from the given object's Ruby class and #id method.

This is especially useful with ActiveRecord instances, which have a persisted #id and will hence **generate the same selector o...

Background information about session storage in Rails

Rails has a default mechanism to store the session in the CookieStore. This is a cookie which holds the entire user session hash in the browser. This cookie is serialized, encoded with base64, and signed.

How Devise handles authentication

Devise uses this CookieStore. To track a users session, a salt is stored in the session ...

When you need to store structured data (like Ruby hashes) in a single database column with ActiveRecord, a simple way is to use PostgreSQL's jsonb columns. ActiveRecord will automatically serialize and deserialize your Hash to and from JSON, and you can index JSON paths for fast reads.

As an alternative, ActiveRecord::Store offers a way to store hashes in a single database column. This card will show you how to migrate those hashes in an ActiveRecord::Migration by example:
...

TL;DR

Append your locale keys with _html to have them marked as html_safe and translate them with = t('.text_html').

When you're localizing a Rails application, sometimes there is this urge to include a little HTML. Be it some localized link, or a set of <em> tags, you'd like to have it included in the locale file. Example:

# Locale file
en:
  page:
    text: 'Please visit our <a href="https://www.corporate.com/en">corporate website</a> to learn more about <em>the corporation</em>.'
    
# HAML
= t('.text')
    
# D...

If your rails application is unable to send mails, it might be useful to debug your settings using the rails console. Here is a snippet that shows the current settings and lets you send a test mail directly from the console:

mailer = ActionMailer::Base.new

# check settings:
mailer.delivery_method # -> :smtp
mailer.smtp_settings # -> { address: "localhost", port: 25, domain: "localhost.localdomain", user_name: nil, password: nil, authentication: nil, enable_starttls_auto: true }

# send mail:
mailer.mail(from: 'sender@example.com', ...

When you have a large PG database, you may want to find out which tables are consuming the most disk space.
You can easily check this using the following SQL statement from the PostgreSQL wiki.

SELECT nspname || '.' || relname AS "relation",
    pg_size_pretty(pg_total_relation_size(C.oid)) AS "total_size"
  FROM pg_class C
  LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
  WHERE nspname NOT IN ('pg_catalog', 'information_schema')
    AND C.relkind <> 'i'
    AND nspname !~ '^pg_toast'
  ORDER BY pg_tot...

The attached article explains options you have to store the order of items in a database table.

The simplest solution of course is to use a position column. However the author explores some alternatives where you don't need to update multiple rows when you move a single item.

Boot partitions from installations prior to the 16.04 era are terribly small. When you install updates and encounter errors due to a full /boot partition, consider risizing it.

If you can't do the steps described below, ask someone experienced to help you out.
This has worked 100% so far. 1 out of 1 tries. ;)

Scenario A: There is unassigned space on your physical drive

When there is some unpartitioned space on your drive, increasing the size of /boot is actually very easy (even though the list below is rather long). It only takes a...

Don't sum up columns with + in a sql-query if NULL-Values can be present.

MySQL and PostgreSQL cannot sum up NULL values with the + value. The sum value will be NULL.

MySQL:

mysql> select 1 + 2 + 3;
+-----------+
| 1 + 2 + 3 |
+-----------+
|         6 |
+-----------+
1 row in set (0,00 sec)

mysql> select 1 + NULL + 3;
+--------------+
| 1 + NULL + 3 |
+--------------+
|         NULL |
+--------------+
1 row in set (0,00 sec)

Postgres:

test_database=# select 1 + 2 + 3;

 ?column? 
----------
        6
(1 row)

t...

New features:

geordi delete_dumps [directory]

Recursively search for files ending in *.dump and offer to delete those. When no argument is given, two default directories are searched for dump files: the current working directory and ~/dumps (for dumps created with geordi).

geordi drop_databases

Delete local MySQL/MariaDB and Postgres databases that are not whitelisted.

Authentication is handled via PAM for Postgres and MariaDB, via .my.cnf with fallback to mysql -p for MySQL. Different connection methods can be chosen via ...

You might have some trouble running a Rails LTS 2 app with MySQL 5.7.

If you don't want to hack Mysql 5.6 into your modern Ubuntu or use the MySQL sandbox, you might want to try MariaDB 10.x.

MariaDB 10.x should work with both old and new Rails applications.

[Switch to MariaDB](https://makandracards.com/makandra/468343-how-...

MySQL and MariaDB have an SQL mode setting which changes how MySQL behaves.

The SQL mode value is comprised of multiple flags like "STRICT_TRANS_TABLES, NO_ZERO_IN_DATE". Each flag activates or disables a particular behavior.

The default SQL mode varies widly between versions of MySQL and MariaDB. In general, more recent versions of MySQL and MariaDB have stricter settings than older versions, and MySQL has stricter settings than the more liberal MariaDB.

If your app explodes ...

On your local system that only hosts non-critical development data and only you have access to, you can store MySQL's root password in your home directory so you can use mysql commands without prompt for passwords, i.e. when doing batch processing.

Of course, this has security implications. The password must be stored in plain text, so this method is out of the question if there's any confidential data in your databases. Assuming diligent screen-locking, an encrypted hard disk and correct permissions set on your credential file, it shoul...

Running rails server will start a local server that you can access via http://localhost:3000.

When you are working on multiple web apps, they will likely set cookies with generic names on localhost. This is annoying, since you will sign out your current user whenever you switch to another app.

A better way is to use our own daho.im service. All daho.im subdomains resolve to your local IP (127.0.0.1). That means you can use a different hostname for different apps, and you will stay logged in in each app:

http://foo-ap...

Your default postgres user is named like your linux user. That default user has limited access privileges, which can cause issues such as:

• DatabaseCleaner needs to disable foreign key constraints before it can wipe the database.
• Importing a remote dump with geordi
• Asking Postgres to show the storage path of a database

Doing these things without a superuser will show a Postgres error or (in Ruby) raise PG::InsufficientPrivilege.

To do so, the application's PostgreSQL user must be a superuser. ...

mysql> SELECT @@global.version;
+------------------+
| @@global.version |
+------------------+
| 5.6.30           |
+------------------+
1 row in set (0,00 sec)

MySQL 5.6 Reference Manual says "BLOB and TEXT columns cannot have DEFAULT values".

If you want to run migrations in development here are two variants which might help. If you are not sure about the side effects (e.g. your application is broken when it doesn't set additional default values on application side, too...

If you want to make a screenshot of a website that works well in print or on a high-DPI screen (like Apple Retina displays), here is how you can capture a high-resolution screenshot.

You can do this without an addon:

• Open the website
• If you have multiple monitoros:
  • Resize the Chrome window so it covers multiple monitors (in Linux you can hold ALT and resize by dragging with the right mouse button)
  • Zoom into the page using CTRL + and CTRL - so it covers most of the window area. Leave a little padding on the left and right so...

Understanding your type of cronjob

Some cronjobs must only run on a single server. E.g. when you run nightly batch operations on the database, it should probably run on a single server. Running it on multiple servers would likely result in deadlocks or corrupt data.

Some cronjobs must always run on all servers. E.g. starting a sidekiq process on reboot.

Configuring whenever

If not configured otherwise, cronjobs defined in whenever's `s...

Enumerable#all? returns true for an empty collection. This totally makes sense but you have to think about it when making assumptions on relations which might be empty.

[].all?(&:will_never_be_called_here) => true

Example with empty collection

class Researcher < ActiveRecord::Base
  has_many :papers
end

class Paper
  validates :topic, inclusion: { in: ['computer_science', 'mathematics', 'economy'] }
end

Easy goal: Delete all researches who write onl...

Font Awesome version 5 changed some icon names, and introduces new prefixes fab, far, and fas.

There is a JavaScript shim that you can use as a "quick fix". It allows you to keep v4 icon names on v5.

The linked page includes details on using that, and a migration guide including a list of icon renames.