Redmine

For me it was hard to figure out specific basic things in respect to redmine I hope what comes next helps others:

Start / Stop / Restart Redmine / WEB-Server¶

As far as I understand it is not possible to start Redmine, what you do is you start or re-start the WEB server process that is the host-environment for Redmine. Here the commands in case you use an Apache2 server:
Initial start:
sudo systemctl start apache2
Restart:
sudo systemctl restart apache2
Restart including syntax check of configuration files (e.g. redmine.conf)
sudo apachectl graceful
Stop Redmine:
sudo systemctl stop apache2

Redmine Home Directory¶

To figure out where your redmine-root directory is, you look for a folder that contains the following files:
`config.ru`, `Rakefile`, `Gemfile`.
This directory is refered to as RAILS_ROOT variable in the Redmine-Plugin-Guide Plugins,
while other guys refer to it as "REDMINE_HOME".
This variable does not exist, if you think it is helpful and makes life easier, you have to specify it
in your user .bashrc-file; add at the end of this file (you need to log-off/-in before it becomes effective):

# ### Redmine environment variable #########################
# ## Variable RAILS_ROOT is equal to the folder which contains 
# ## the files `config.ru`, `Rakefile`, `Gemfile`
# ## see: https://www.redmine.org/projects/redmine/wiki/Plugins
export RAILS_ROOT="/usr/share/redmine" 

Plugin-Directory:¶

After installation of Redmine you will find in the subdirectory /lib of the RAILS_ROOT-directory
a folder called plugins, this is not the destination of your plugins that you might want to install.
The plugin-folder my not exist and its location is:
$RAILS_ROOT/plugins

Have fun :-)