A reworked version of the web application Airtime-2.5.x to install on Ubuntu 17.10 with PHP5.6

sudo add-apt-repository ppa:ondrej/php
sudo add-apt-repository ppa:flexiondotorg/audio
sudo apt-get update

sudo apt-get install php5.6 php5.6-bcmath

Apache:
sudo a2dismod php7.2 ; sudo a2enmod php5.6 ; sudo service apache2 restart

CLI:
sudo update-alternatives --set php /usr/bin/php5.6

sudo apt-get install mp3gain

./install

Open a browser and enter in the address bar localhost or Your IP address to enter the configuration page of Airtime!

sudo service airtime-playout start
sudo service airtime-liquidsoap start
sudo service airtime-media-monitor start

When you add audio files, these files are stored in /tmp/plupload and if apache uses privacy, then it is better to disable this:
nano /etc/systemd/system/multi-user.target.wants/apache2.service
And change the value PrivateTmp=true to false

Also for some, it is possible to use storage of audio files in the following directories with permissions 777:

/srv/airtime/stor/
/tmp/plupload