The /etc/hosts file is a local DNS resolver that maps hostnames to IP addresses before querying external DNS servers. Each entry follows this format:

IP_address hostname [alias1] [alias2] ...

For your specific case wanting to resolve multiple domains to 81.174.66.48, the proper format would be:

81.174.66.48 nerto.it nerto eventlog.it eventlog.in

Or alternatively as separate entries (though less efficient):

81.174.66.48 nerto.it nerto
81.174.66.48 eventlog.it
81.174.66.48 eventlog.in

After editing, verify the changes using these commands:

ping nerto.it
ping eventlog.in
host eventlog.it
nslookup nerto

Remember to clear your DNS cache if needed:

# Linux
sudo systemd-resolve --flush-caches

# macOS
sudo dscacheutil -flushcache

# Windows
ipconfig /flushdns

For testing multiple environments, you might want to create backup versions:

# Create backup
sudo cp /etc/hosts /etc/hosts.bak

# Restore if needed
sudo cp /etc/hosts.bak /etc/hosts

For complex setups, consider using wildcard DNS locally with dnsmasq:

# Install dnsmasq
sudo apt install dnsmasq

# Configure
echo "address=/it/81.174.66.48" | sudo tee -a /etc/dnsmasq.conf
sudo systemctl restart dnsmasq

The /etc/hosts file follows a specific format where each line contains:

IP_address    hostname1    hostname2    ...

For your case with IP 81.174.66.48 and domains nerto.it, eventlog.it, etc., the correct syntax would be:

81.174.66.48    nerto.it nerto eventlog.it eventlog.in

The issue with your initial attempt was splitting the domains across multiple lines for the same IP. The proper way is to list all hostnames on a single line with the IP address.

Example of incorrect approach:

# This won't work as expected
81.174.66.48 nerto.it nerto
81.174.66.48 eventlog.it
81.174.66.48 eventlog.in

After modifying /etc/hosts, test with:

ping nerto.it
ping eventlog.in
dig +short eventlog.it

For developers needing more complex setups:

# Local development with multiple domains
127.0.0.1    localhost myapp.dev api.myapp.dev admin.myapp.dev

Remember that modern systems typically check DNS before /etc/hosts. To prioritize local resolution:

# In /etc/nsswitch.conf (Linux)
hosts: files dns

Windows equivalent (C:\Windows\System32\drivers\etc\hosts):

81.174.66.48    nerto.it
81.174.66.48    eventlog.it
81.174.66.48    eventlog.in

Note Windows requires separate lines per hostname.