When working with OS X Mountain Lion (10.8), many developers get confused by the traditional Unix DNS resolution mechanisms not behaving as expected. The key revelation comes from that /etc/resolv.conf notice:

#
# Mac OS X Notice
#
# This file is not used by the host name and address resolution
# or the DNS query routing mechanisms used by most processes on
# this Mac OS X system.
#
# This file is automatically generated.
#

Instead of resolv.conf, macOS uses its own system configuration daemon (configd) and the System Configuration framework for DNS resolution. The primary files controlling this are:

• /etc/hosts - Still used for static entries
• /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist - The mDNS responder
• Network preference pane settings

For your specific case where host servername isn't resolving an entry from /etc/hosts, here's how to fix it:

# 1. Edit your hosts file (requires sudo)
sudo nano /etc/hosts

# 2. Add your entry (example format)
192.168.1.100    servername

# 3. Flush the DNS cache (OS X Mountain Lion specific)
dscacheutil -flushcache
killall -HUP mDNSResponder

The host command might not always respect the hosts file. Try these alternatives:

# Using dig (more reliable for testing)
dig servername

# Using nslookup
nscutil --dns
nslookup servername

# Using the system resolver directly
python -c "import socket; print(socket.gethostbyname('servername'))"

For system-wide DNS server configuration (instead of just hosts file entries):

# View current DNS configuration
scutil --dns

# Set DNS servers via command line (example)
networksetup -setdnsservers Wi-Fi 8.8.8.8 8.8.4.4

If you're still having issues:

1. Check permissions on /etc/hosts (should be 644)
2. Verify no trailing spaces or malformed entries
3. Test with different tools as shown above
4. Restart mDNSResponder: sudo launchctl unload /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist followed by load

---

If you've checked your /etc/resolv.conf on OS X Mountain Lion, you might have noticed this message:

#
# Mac OS X Notice
#
# This file is not used by the host name and address resolution
# or the DNS query routing mechanisms used by most processes on
# this Mac OS X system.
#
# This file is automatically generated.
#

This explains why your manual DNS changes in this file don't work. OS X uses a different system for name resolution.

OS X uses the scutil (System Configuration Utility) to manage DNS settings. Here's how to view your current DNS configuration:

scutil --dns

For network interface-specific settings:

scutil --nwi

To add a custom host entry that will work system-wide:

1. Edit /etc/hosts (requires sudo):

sudo nano /etc/hosts

Add your entry like:

192.168.1.100   myserver.local

Flush the DNS cache:

sudo dscacheutil -flushcache
sudo killall -HUP mDNSResponder

The host command bypasses the local hosts file by default. To test your entry, use:

ping myserver.local

Or use dscacheutil to query the cache:

dscacheutil -q host -a name myserver.local

For more control, create a custom resolver:

sudo mkdir /etc/resolver
sudo nano /etc/resolver/mydomain

Add content like:

nameserver 8.8.8.8
search mydomain.local

Check all name resolution sources:

nslookup myserver.local
dig myserver.local

Remember that changes might take a few moments to propagate through all system components.