Tag Archives fordocker

Debugging cron on Docker

I had the issue of cronjobs not working (correctly) on my Docker instances.

This is what I did to fix it:

  1. Set correct permissions: chmod 0600 /etc/cron.d/cronjob
  2. Set correct owner: chown root /etc/cron.d/cronjob

When it failed, I could not find the logs of why it failed.
In order to see the output of the failed cronjobs, I installed postfix (because the output of cronjobs is being mailed) and I installed rsyslog

  1. Install postfix:
    apt-get update; apt-get install -y postfix; mkfifo /var/spool/postfix/public/pickup; service postfix restart
  2. Install rsyslog:
    apt-get update; apt-get install -y rsyslog; rsyslogd &

Now, whenever a cronjob failed, I could find output in either two locations:

  1. In the syslog: /var/log/syslog
  2. In the mail sent to root: /var/mail/root

Install Docker on Ubuntu 20.04

That’s an easy and quick think to do!

sudo apt update
sudo apt install docker.io

# start docker now, and on system reboot
sudo systemctl start docker
sudo systemctl enable docker

# check the version
docker --version
  Docker version 19.03.8, build afacb8b7f0

Don’t forget to add your user to the docker group, otherwise you’ll get permission denied errors

docker ps
  Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http://%2Fvar%2Frun%2Fdocker.sock/v1.40/containers/json: dial unix /var/run/docker.sock: connect: permission denied

To add your account to the docker group:

sudo usermod -a -G docker paul

Don’t forget to logout and login again!

Docker on Windows: /usr/bin/env: bash\r No such file or directory

Getting the following error when you want to start your Docker container on Windows: /usr/bin/env: bash\r : No such file or directory


I discovered that another fix is to do dos2unix <file>

dos2unix <file with the issues>

Try that if you’re on Windows or working with others who work on Windows.


I found several topics with several fixes. But what fixed it for me was:

Solution: Setting the line-endings correctly

  • In my editor: \n
  • In git: git config --global core.autocrlf false

I chose the \n line ending as this is stated in PSR-12: 2.2 Files:
All PHP files MUST use the Unix LF (linefeed) line ending only.

I use PHPStorm and had to go to
Settings > Editor > Code Style > tab General > Unix and macOS (\n)

NOTE: you may have to do the following to fix files with the wrong line-endings:

  • remove the built Docker image on Windows: first list docker images and then delete: docker rmi <imagename>
  • fix the line-ending of the file. You might do that by removing the newline and adding a new one. Don’t forget to save, commit and push

Docker opschonen: vrije ruimte terugkrijgen

Als je Docker een tijdje gebruikt hebt, dan kan het zeker lonen om de boel eens op te schonen. Door items te verwijderen die je niet meer nodig hebt kun je een hoop ruimte vrijmaken.


Voer deze commando’s uit om alles op te ruimen

docker system prune
docker images --no-trunc | grep '<none>' \
    | awk '{ print $3 }' \
    | xargs docker rmi
docker ps --filter status=dead --filter status=exited -aq \
  | xargs docker rm -v
docker volume ls -qf dangling=true | xargs docker volume rm
Continue reading

Set up NGINX as a proxy for your Docker containers

Recently I’m a fan of serving docker containers over serving Virtual Hosts using a webserver.

In order to use regular domainnames without ports, I set up Nginx to receive the request on the domainname and let it forward the request to the relevant Docker container on the specific port it is running on.


Imagine I have a Docker webserver-container hosting my app. It runs on my server exposing port 8080. I use the URL app.pauledenburg.com.

I don’t want people to use http://app.pauledenburg.com:8080 but just the URL without the port



I use nginx for this:

server {
    listen 80;
    server_name app.pauledenburg.com;

    location / {
        proxy_pass http://localhost:8080;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;

And now add SSL to it 🙂

Complete ELK-stack example with Docker

I wanted a quick setup for an Elasticsearch Logstach and Kibana (ELK-)stack to work with. But searching on the internet gave me too many long-winded not really working examples.

That’s why I created this page. Use it to quickly get up-and-running with an ELK-stack of your own.

Create the file docker-compose.yml

# file: docker-compose.yml
version: "3"

    image: sebp/elk
      - "5601:5601"
      - "9200:9200"
      - "5044:5044"
      - MAX_MAP_COUNT=262145
      - KIBANA_START=1
      - TZ="Europe/Amsterdam"
      - elk-data:/var/lib/elasticsearch


Now start up with docker-compose up -d. That’s it!

5601: endpoint for Kibana
9200: endpoint for elastic search

Add some security

Don’t leave your elastic-search open for everyone.

Add some basic security by adding a .htpasswd config to your webserver.

$ sudo sh -c "echo -n 'myelasticuser:' >> /etc/nginx/.htpasswd"
$ sudo sh -c "openssl passwd -apr1 >> /etc/nginx/.htpasswd"
Verifying - Password:

Add it to your webserver, like nginx.

server {
    listen 80 default_server;
    listen [::]:80 default_server ipv6only=on;

    root /var/www/html;
    index index.html index.htm;

    server_name localhost;

    location / {
        try_files $uri $uri/ =404;
        auth_basic "Restricted Content";
        auth_basic_user_file /etc/nginx/.htpasswd;

Reload nginx.

$ sudo nginx -t
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful

$ sudo service nginx reload

Some notes

I chose the Docker image of sebp because he’s got great documentation. Go check it out!

Especially the part with the Frequently Encountered Issues.

There, you’ll see that you’ll:

  • need 4GB of memory for the Docker container
  • need to set the amount of virtual memory on linux by setting the max map count:sudo sysctl -w vm.max_map_count=262144

SonarQube with Postgres on docker-compose

[updated 2022-08-08]

Struggling to get a working environment with SonarQube and PostgreSQL?

Use the following docker-compose file and be up and running in minutes.

It is as ‘bare’ as possible:

  • use of official Docker images for both PostgreSQL and SonarQube
  • no other configuration required
  • use of volumes so you can backup your data

Recommended system specs

  • >= 3GB of RAM
# file: docker-compose.yml

version: "3"

    image: sonarqube:9-community
    # platform: linux/amd64  # uncomment this when using Mac M1
    restart: unless-stopped
      - SONARQUBE_JDBC_URL=jdbc:postgresql://db:5432/sonarqube
      - "9000:9000"
      - "9092:9092"
      - sonarqube_conf:/opt/sonarqube/conf
      - sonarqube_data:/opt/sonarqube/data
      - sonarqube_extensions:/opt/sonarqube/extensions
      - sonarqube_bundled-plugins:/opt/sonarqube/lib/bundled-plugins

    image: postgres:14.4
    # platform: linux/amd64  # uncomment this when using Mac M1
    restart: unless-stopped
      - POSTGRES_USER=sonar
      - POSTGRES_DB=sonarqube
      - sonarqube_db:/var/lib/postgresql
      # This needs explicit mapping due to https://github.com/docker-library/postgres/blob/4e48e3228a30763913ece952c611e5e9b95c8759/Dockerfile.template#L52
      - postgresql_data:/var/lib/postgresql/data


Start this stack with the following command:

# start the containers
docker-compose up -d

You can reach your SonarQube instance at http://localhost:9000

Use the default credentials admin/admin to login.

Useful links: