For Ubuntu 16.04, you can find the global configuration file here:
/etc/apache2/apache2.conf
Therein it defines some LogFormat
directives.
LogFormat "%v:%p %h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" vhost_combined
LogFormat "%h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" combined
LogFormat "%h %l %u %t \"%r\" %>s %O" common
LogFormat "%{Referer}i -> %U" referer
LogFormat "%{User-agent}i" agent
The out-of-the-box virtual host configuration file is here:
/etc/apache2/sites-available/000-default.conf
And inside you will find that it declares:
CustomLog ${APACHE_LOG_DIR}/access.log combined
The combined
alias refers to the second LogFormat
in the aforementioned global config:
"%h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\""