Cannot modify the instance class because there are no instances of the requested class available in the current instance’s availability zone

When you change the instance type of an AWS RDS instance, the availability zone of the instance has to have available capacity of the selected type.

Some older availability zones (us-east-1a) have more old instance types than new types available. If the instance type you selected is not available in the current zone of the instance you get the error message:

We’re sorry, your request to modify DB instance … has failed.

Cannot modify the instance class because there are no instances of the requested class available in the current instance’s availability zone. Please try your request again at a later time.

To upgrade an RDS instance to a new type that is not available in the current availability zone:

  1. Find an AZ that has the desired instance type
    • Try to launch an instance with the new instance type and see which zones have available capacity
  2. Change the RDS instance to multi-AZ
    • Click the Modify button and change the instance to multi-AZ
  3. If the secondary instance is not created in a zone that has available capacity of your desired instance type, change the instance back to single-AZ and return to step 2, to set it to multi-AZ again.
  4. Reboot with failover to the secondary instance to make it the primary instance in the new availability zone
    • Click the Actions button and select Reboot
    • Select Reboot with failover
  5. Change the instance back to single-AZ
  6. Upgrade the instance type

Exit from Bash script on error without closing the terminal window

To terminate the script in case of an error, we can use the “-e” option.

set -e


#!/bin/bash -e

When a bash script is

  • “sourced”,
  • called from an alias with a leading dot like my-alias='. /my-script to execute in the same process, or
  • a function is executed from a terminal window

and the script exits on an error, it closes the terminal window.

To keep the terminal open, execute the script in a subprocess. It is easy to update existing scripts. Enclose the main part of the script in parentheses to open a new subprocess and add the “set -e” option to it. In case of an error the script terminates the subprocess and returns to the terminal session.


my_function() {

  set -e
  my entry point to the script

Error: Failed to install cookbooks from lockfile

When the CI/CD pipeline loads dependency cookbooks from GitHub and the kitchen converge process throws the error:

Error: Failed to install cookbooks from lockfile
Reason: (CookbookOmnifetch::NotACookbook) The resource at ‘/…’ does not appear to be a valid cookbook. Does it have a metadata.rb?

make sure the remote revisions of the dependency cookbook match in the caller and the dependency cookbook’s Policy Lock files and both files are pushed to GitHub.

"scm_info": {
  "scm": "git",
  "remote": "",
  "revision": "22592d58489abb53316638ce9edfe5ee3742c5cc",

Install Python 3 on MacOS

The MacOS comes with an old version of Python 2. For new software development Python 3 is the recommended version. Replacing the original Python 2 with Python 3 can cause instability in the MacOS. There are multiple ways to install Python 3 and keep Python 2 pn the Mac. This is the most recommended process:

Use Pyenv

Pyenv is a Python version manager. It is recommended, because using it we can install and utilize multiple Python versions.

Install Pyenv

We will use Homebrew to install Pyenv

brew install pyenv

Install the latest stable version of Python with Pyenv

Check for the latest stable release.

pyenv install 3.9.6

Set the new Python version the default

pyenv global 3.9.6
# check if the change took effect
pyenv version

Configure your shell to use Pyenv for Python version management

Add these lines to your .bashrc, .zshrc or .bash_profile file

PATH=$(pyenv root)/shims:$PATH

if command -v pyenv 1>/dev/null 2>&1; then
  eval "$(pyenv init -)"

Check the default Python version

Open a new terminal window fo these configuration changes to take effect

python --version


During the installation I have encountered the following error messages

Error: The following directories are not writable by your user:

You should change the ownership of these directories to your user.
sudo chown -R $(whoami) /usr/local/bin

To set you as the owner of the /usr/local/bin directory execute

sudo chown -R $(whoami) /usr/local/bin

homebrew-core is a shallow clone.
To brew update, first run:
git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core fetch –unshallow

To update the shallow clone of the repository from GitHub execute

git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core fetch --unshallow

Error: The following formula cannot be installed from bottle and must be
built from source.
Install the Command Line Tools:
xcode-select –install

To install the xcode command line developer tools execute

xcode-select --install

Install and configure iTerm2

  1. Download iTerm2 from
  2. Double click the downloaded ZIP file to extract the application,
  3. Move the iTerm application to Applications.

iTerm2 configuration

Use .bashrc for configuration

When you start iTerm, it reads its own config file, ~/.zshrc To keep using the standard ~/.bashrc config file

  • Create the ~/.zshrc file and have only one line in it:source ~/.bashrc

Set case-insensitive tab completion

Add these lines to the ~/.zshrc file

# Set case insensitive comparison when lower case letters are typed.
# Upper case typed letters only match upper case file names
zstyle ':completion:*' matcher-list 'm:{a-z}={A-Za-z}'
autoload -Uz compinit && compinit

Enable unlimited scroll back

  1. Start iTerm2 and open the preferences window by pressing ⌘, (command-comma)
  2. On the Profiles, Terminal tab click the Unlimited scrollback check box.

Set the highlight color

By default the highlighted text just a little different from the rest. When we search for something, it is hard to notice the found text.

To change the highlighted text color

  1. Start iTerm
  2. In the iTemr2 menu select Preferences…
  3. On the Profiles, Colors tab set the color of the Selection and Selected Text

Start iTerm2 from Finder

To be able to open iTerm2 in any folder from Finder follow the steps below based on

  1. Start Automator,
  2. Select Quick Action and click Choose,
  3. On the top of the screen set Workflow receives selected to files and folders,
  4. Set in to Finder,
  5. On the second side bar from the left double click Run AppleScript to open the editor window,
  6. Paste the code from the website referenced above into the editor window replacing the sample script in the editor window,
  7. In the File menu save the script,
  8. Do not run it, it does not execute in the Automator.

To use it

  1. Open Finder and navigate to the location you want to work in,
  2. Right click a folder to work in that folder or a file to work in the current folder
  3. Select ServicesiTerm2 in Finder

“Solarized” color scheme

  1. Download the color scheme to the Desktop with the following Bash command:curl -o ~/Desktop/solarized.itermcolors
  2. Import the color scheme to iTerm2
    • Press ⌘, (command-comma) to open the Preferences window
    • Select Profiles
    • In the lower right corner of the Colors tab click the Color Presets… drop down
    • Select Import
    • On the Desktop select the downloaded solarized.itermcolors file
    • In the  Color Presets… drop down select Solarized Dark

 Meslo Powerline font

  • Import the Meslo Powerline font with the following bash command:git clone && cd fonts && ./
  • Select the font in iTerm2
    • Press ⌘, (command-comma) to open the Preferences window
    • Select Profiles
    • On the Font section of the Text tab click the Change Font button
    • Select the 12pt Meslo LG L Regular for Powerline

Make the prompt shorter

to remove your username@computername from the prompt

  • Edit the ~/.bashrc file
  • Add the following lineDEFAULT_USER=”YOUR_USER_NAME”

Colored prompt

To color the prompt:

  • Download the agnoster theme
sh -c "$(curl -fsSL"
  • Edit the ~/.bashrc file and set the ZSH_THEME to ZSH_THEME=”agnoster”

More configuration suggestions are at

Information on how terminals read settings at

chef push always regenerates the revision id and Policyfile.lock.json

If the chef update and chef push commands always regenerate the Policyfile.lock.json file and the revision_id in it, make sure the Chef cookbook contains the chefignore file and it also references all possible Policyfile lock files:

# Policyfile #

If a cookbook file changes, a new Policyfile.lock.json is generated during chef push.

chef update and chef push always check the cookbook files not listed in the chefignore file, and if there is a change, regenerate the Policyfile.lock.json including the revision_id element in it.

Failed to complete #create action: [undefined method `[]’ for nil:NilClass] on …

When we launch a test instance with Chef Test Kitchen, we may get the error message:

—–> Starting Test Kitchen (…)
—–> Creating …
>>>>>> Class: Kitchen::ActionFailed
>>>>>> Message: 1 actions failed.
>>>>>> Failed to complete #create action: [undefined method `[]’ for nil:NilClass] on …
>>>>>> ———————-
>>>>>> Please see .kitchen/logs/kitchen.log for more details
>>>>>> Also try running kitchen diagnose --all for configuration

Missing AMI

This can be the result of a missing AWS AMI referenced in the kitchen.yml file. Check if the AMI is still available in the AWS account you are working in.

Tejes vajas fonott császárzsemle

Igazi békebeli fonott császárzsemle receptet találtunk Gábornál.


TangZhong (előtészta)
260 ml tej
40 g liszt

Az élesztőhöz
230-250 ml tejben
24 g élesztő
egy csipet cukorral felfuttatjuk

A tésztához
650 g finom liszt
10- 12 g só
12 g cukor
35 g vaj


Felfuttatjuk az élesztőt

Mielőtt forrni kezdene a tej, lecsökkentjük a hőmérsékletet és gyors keverés mellett lassan beleöntjük a lisztet. Összemelegítjük a lisztet a tejjel, a video szerint, lefedjük, lehűtjük.


Átszitáljuk a lisztet a dagasztó tálba
hozzáadjuk az előtésztát
A sót, cukrot, A felfuttatott élesztőt
Jól kidagasztjuk
Amikor a tészta szépen felvette a lisztet  és összeállt, hozzáadjuk a vajat
Ha a tészta elkészült, áttesszük egy kiolajozott kelesztő tálba.
A tészta érés ideje a tálban 45 perc

Kivesszük a tésztát és elosztjuk 12-13 db, kb . 95 gr-os darabra
Gömbölyítjük a tésztákat, nem lisztezzük a deszkát
Letakarva 5-10 percet pihentetjük

Megformázzuk a tésztát

Hajtogatjuk, hurkákat készítünk, mint a kalács fonásnál
Kinyújtjuk a hurkákat 40-45 cm hosszúra
Vékonyan belisztezzük a deszka hátsó részét
fonás előtt meghempergetjük a tésztát, hogy ne tapadjon össze
Hurkot kötünk, hogy megformázzuk a császárzsemlét
Sütőpapírral bélelt tepsire tesszük a felét, egy másik tepsire a másik
Leterítjük egy konyharuhával és egy műanyag fóliát (zacskót) teszünk rá
Kelesztés 50-70 perc


A sütőt előmelegítjük 230 C °-ra, alsó-felső sütésre, az aljába vizet teszünk egy edényben.

Sütés előtt, mielőtt a sütőbe tesszük, a tésztákat vízzel átspricceljük.
Betesszük a tepsit a sütőbe, 210 C°-ra csökkentjük a hőmérsékletet, 16-20 percig sütjük,  a vizet 12 perc után eltávolítjuk.
Ha a zsemlék alja nem sült meg eléggé, a zsemléket letakarhatjuk alufóliával, esetleg lejjebb tesszük a tepsit, így sütjük 4-8 percig ( 16-20 perc összesen )

Sütés után ismét vízzel lespricceljük.

Gábor web oldalalán minden receptjét megtaláljátok:

Gábor videóját itt láthatjátok

Friss élesztő és szárított élesztő összehasonlítása

A legegyszerűbben a következő formulával hasonlíthatjuk össze a friss élesztőt és a szárított élesztőt:

1 g szárított élesztő 3 g friss élszetőnek felel meg.

Ha nincs eléggé érzékeny mérlegünk, 1 teáskanál ( 3 g ) szárított élesztő 9 g friss élesztőnek felel meg.

extra characters at the end of n command

When you use sed to insert a template file into another file with the command

# $1 String to insert
# $2 File to insert to
# $3 String to insert after
sed  "/$3/a\\
" $2 > tmp && mv tmp $2	

and get the error message

extra characters at the end of n command

Make sure the template file supplied in $1 does not have an empty line at the top.