Works for me on Ubuntu 20.04.

Add to you project's docker-compose.yml

(https://github.com/docker/for-linux/issues/264#issuecomment-772844305)

services:
  your_php_service_name:
    extra_hosts:
      - host.docker.internal:host-gateway

In your CLI run export XDEBUG_TRIGGER=1 && export PHP_IDE_CONFIG="serverName=host.docker.internal" to start xdebug with the request.

Thanks @LazyOne for his comment to the question with the solution.

Inside of your Docker container don't use remote_host. Also, you don't have to expose any additional ports in Docker or in Vagrant.

Here is my xdebug.ini file that works with PHP 5.6

zend_extension=/usr/local/lib/php/extensions/no-debug-non-zts-20131226/xdebug.so
xdebug.remote_enable=1
xdebug.remote_autostart=0
xdebug.remote_handler=dbgp
xdebug.remote_port=9000
xdebug.remote_connect_back=1

Make sure that PhpStorm (2016.1 in my case) is configured correctly

• Languages & Frameworks -> PHP -> Servers -> localhost -> localhost : 80 Xdebug
• Languages & Frameworks -> PHP -> Debug -> Xdebug -> Debug port: 9000
• Languages & Frameworks -> PHP -> Debug -> Xdebug -> Can accept external connections
• Languages & Frameworks -> PHP -> Debug -> DBGp Proxy -> Port 9000

Once this is done find Listen for debugger connections icon in PhpStorm in the toolbar and click it.

If you want to call it from a command line remember to include XDEBUG_SESSION cookie, i.e.

curl 'http://localhost' -sSLI -H 'Cookie: XDEBUG_SESSION=xdebug'

If you use Firefox install The easiest Xdebug and enable it in the toolbar.

I solved this by adding the following lines into my Docker file:

# "xdebug-2.9.0" for PHP<=7.4 — "xdebug" (3) for PHP>=8
ARG XDEBUG_VERSION="xdebug-2.9.0"

FROM php:7.0-apache

RUN a2enmod rewrite

RUN docker-php-ext-install pdo pdo_mysql

RUN yes | pecl install ${XDEBUG_VERSION} \
    && echo "zend_extension=$(find /usr/local/lib/php/extensions/ -name xdebug.so)" > /usr/local/etc/php/conf.d/xdebug.ini \
    && echo "xdebug.remote_enable=on" >> /usr/local/etc/php/conf.d/xdebug.ini \
    && echo "xdebug.remote_autostart=off" >> /usr/local/etc/php/conf.d/xdebug.ini


COPY php.ini /usr/local/etc/php/
COPY . /var/www/html/