When text renders differently in Firefox and Chrome, it may be caused by a font alias that both browsers handle differently.

Situation

A machine running Linux, and a website with the Bootstrap 3 default font-family: "Helvetica Neue", Helvetica, Arial, sans-serif.

Issue

Anti-aliasing and kerning of text looks bad in Firefox. Worse, it is rendered 1px lower than in Chrome (shifted down).

Reason

Firefox resolves "Helvetica" to an installed ["TeX Gyre Heros", which is its Ghostscript clone](https://www.fontsquirrel.com/fonts/...

When using Chrome for Selenium tests, the chromedriver binary will be used to control Chrome. To debug problems that stem from Selenium's Chrome and/or Chromedriver, you might want to enable logging for the chromedriver itself. Here is how.

Option 1: Use Selenium::WebDriver::Service

In your test setup, you may already have something like Capybara::Selenium::Driver.new(@app, browser: :chrome, options: ...), especially when passing options like device emulation.

Similar to options, simply add an extra key service and pass an inst...

There are several ways to merge two (or more) PDF files to a single file using the Linux command line.

If you're looking for graphical tools to edit or annotate a PDF, we have a separate card for that.

PDFtk (recommended)

PDFtk is a great toolkit for manipulating PDF documents. You may need to install it first (sudo apt install pdftk).
Merging multiple files works like this:

pdftk one.pdf two.pdf cat output out.pdf

Unlike pdfjam, PDFtk should not mess with page sizes but simply joins pages as they are.

...

The issue in this card can occur if the node_modules directory is checked into your Git repository. We usually recommend to exclude node_modules from version control.

In any case you should document which version of node to use in your project in a .nvmrc file.

I saw a strange behaviour after we introduced webpack in one of our projects and finally found out the reason: The person who committed the files used a node version that is older than mine.

Every time I wanted to run my rai...

The rendered font often depends on the local font your system provides, therefore you often find a rule like below in the computed style for an element:

font-family: Menlo,Monaco,Lucida Console,Liberation Mono,DejaVu Sans Mono,Bitstream Vera Sans Mono,Courier New,monospace,serif

This means if your system has a font named Menlo, it will render the text with this font. Otherwise it will try Monaco and so on. For the last two fallback options the system is free to use any monospace font or if not present any serif font. At lea...

When you receive a ZIP file from a Windows user, umlauts and other non-latin1 characters in filenames may look corrupt, and probably will be corrupt when extracting the ZIP file.

The reason is encoding: Such archives are probably using Codepage 850. I am serious, 1987 is calling.

Fortunately, the unzip command can handle such files like so:

unzip -O CP850 file.zip

Interestingly enough, Rubyzip also compresses files that way. Probably so files look alright to Windows users.

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...

The httpclient gem comes with a custom SSL cert store.

While an customizable, application-level cert store is great when you need to deal with broken or self-signed certificates, you usually want to use the cert store from the underlying Linux. The Linux cert store is updated periodically while httpclient's cert store goes out of date and will eventually not be able to verify certs.

To use the cert store from the underlying operating system:

client = HTTPClient.new
client.ssl_config.cert_store...

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. ...

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...

Let's say you have a folder images and want to to move all files in there to a new subfolder public.

cd images
mkdir public
mv !(public) public

The !(public) excludes the new subfolder itself from being moved.

ImageMagick has a command line tool called identify which can read image metadata:

>identify -verbose DSC00136.JPG
Image: DSC00136.JPG
  Format: JPEG (Joint Photographic Experts Group JFIF format)
  Class: DirectClass
  Geometry: 5472x3648+0+0
  Resolution: 350x350
  Print size: 15.6343x10.4229
  Units: PixelsPerInch
  Type: TrueColor
  Endianess: Undefined
  Colorspace: sRGB
  Depth: 8-bit
  Channel depth:
    red: 8-bit
    green: 8-bit
    blue: 8-bit
  Channel statistics:
    Red:
      min: 0 (0)
      max: 255 (1)
      mean: 11...

run-one is a wrapper script that won't run the given command while another instance of it is running. Is brings several utility commands that offer similar behavior.

NAME
       run-one - run just one instance at a time of some command and unique set of arguments (useful for cronjobs, eg)

SYNOPSIS
       run-one COMMAND [ARGS]

       run-this-one COMMAND [ARGS]

       run-one-constantly COMMAND [ARGS]

       keep-one-running COMMAND [ARGS]

       run-one-until-success COMMAND [ARGS]

       run-one-until-failure COMMAND [ARGS]

...

Add the following to /etc/rc.local:

(sleep 3 && echo disable > /proc/acpi/ibm/bluetooth)&

Bluetooth icon will be active for a few seconds, then turn gray.

To create a 10 GB file:

fallocate -l 10G huge_file.dat

You can use three different versions of the regular expression syntax in grep:

• basic: -G
• extended: -E(POSIX)
• perl: -P (PCRE)

Difference between basic and extended:

In basic regular expressions the meta-characters '?', '+', '{', '|', '(', and ')' loose their special meaning; instead use the backslashed versions '?', '+', '{', '|', '(', and ')'.

Difference between extended (POSIX) and perl (PCRE): E.g. \d is not supported in POSIX.

This g...

Easy mode

This method will remove automatically installed packages that no other packages depend on any more. This, of course, includes obsolete kernel versions, with the explicit exception of the currently running kernel, the kernel version that was installed on the system before that and, of course, the latest updated version of the kernel. However, it will also remove any and all other packages that have been marked as installed automatically but have no other packages depending on them. This could lead to unexpected removal of packag...

If your external displays not switching on or showing a weird behavior (for e.g. all displays getting the same configuration all the time) you can fix it by switching off all external displays and re-enabling only one in the first step. Afterwards you can apply your whole configuration via xrandr. This behavior could be a bug in the kernel and may be fixed in linux 4.8.

Example display configuration

Screen 0: minimum 8 x 8, current 5760 x 1200, maximum 32767 x 32767
eDP1 connected 1920x1080+0+0 (normal left inverted right x axis...

When giving a presentation with a projector it is sometimes better to use a dual screen layout instead of a cloned display. If you still want a preview of the projector screen on your primary screen, you can do this:

0. Install x11vnc and a vnc viewer (e.g. xtightvncviewer).

1. Connect the projector.

2. In your system display settings, move the projector to the left or your primary screen (not strictly necessary, but I had weird clipping issues otherwise).

3. Start a vnc server for your second display with

   x11vnc -clip xinera...
   

I've encountered a Ubuntu 16.04 today, where localhost resolved to ::1 instead of 127.0.0.1.

This will not usually make a difference, but could be relevant for firewall policies.

On OSX (real or inside Browserstack), you need different keystrokes for your favorite special characters than you'd use on Linux or Windows.