Fix Apache2 "Could not reliably determine the server's fully qualified domain name" warning

# Apache2 warning:
"Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ServerName"

# set FQDN in /etc/hosts like:
127.0.1.1 srv1.home srv1

# or
sed -i "s|$(hostname) $(hostname)|$(hostname -A)$(hostname)|g" /etc/hosts

# or set ServerName in Apache vHost config

# check
hostname --fqdn

# Info
# sysctl kernel.hostname=srv1