why doesn't text display in jekyll site generator?

Question

I want to launch a site using jekyll, but the problem is that no posts are displayed. I have used the template lanyon. The odd thing is that with the command

bundle exec jekyll serve

The website starts without any problems, but no posts are still displayed.Even changes to the template's content remain unchanged.

This is the content of the config.yml file :

# Dependencies
# markdown:         redcarpet
markdown:           kramdown
# pygments:         true
highlighter:        true

# Permalinks
permalink:        pretty

# Setup
title:            Lanyon
tagline:          'A Jekyll theme'
description:      'A reserved <a href="http://jekyllrb.com" target="_blank">Jekyll</a> theme that places the utmost gravity on content with a hidden drawer. Made by <a href="https://twitter.com/mdo" target="_blank">@mdo</a>.'
url:              http://lanyon.getpoole.com

author:
  name:           'Mark Otto'
  url:            https://twitter.com/mdo

# paginate:         5
jekyll-paginate:    5

# Custom vars
version:          2.0.0

github:
  repo:           https://github.com/poole/lanyon

This is the content of the gemfile file :

source "https://rubygems.org"

# Hello! This is where you manage which Jekyll version is used to run.
# When you want to use a different version, change it below, save the
# file and run `bundle install`. Run Jekyll with `bundle exec`, like so:
#
#     bundle exec jekyll serve
#
# This will help ensure the proper Jekyll version is running.
# Happy Jekylling!
gem "jekyll", "~> 3.8.5"

# This is the default theme for new Jekyll sites. You may change this to anything you like.
gem "minima", "~> 2.0"

# If you want to use GitHub Pages, remove the "gem "jekyll"" above and
# uncomment the line below. To upgrade, run `bundle update github-pages`.
# gem "github-pages", group: :jekyll_plugins

# If you have any plugins, put them here!
group :jekyll_plugins do
  gem "jekyll-feed", "~> 0.6"
end

# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem "tzinfo-data", platforms: [:mingw, :mswin, :x64_mingw, :jruby]

# Performance-booster for watching directories on Windows
gem "wdm", "~> 0.1.0" if Gem.win_platform?

And the packages I used to launch the website:

• redcarpet (3.4.0, 3.3.4)
• ruby 2.5.3p105 (2018-10-18 revision 65156) [x86_64-linux]
• jekyll (3.8.5)
• bundler (1.17.1)
• pygments.rb (1.2.1, 0.6.3)