When setting up Postfix on Ubuntu 12.04 with ZoneMinder integration, many administrators encounter this specific error in mail logs:

warning: hash:/etc/aliases is unavailable. open database /etc/aliases.db: No such file or directory

This occurs when Postfix attempts to access the aliases database but finds either:

• The compiled aliases database (/etc/aliases.db) is missing
• Or the system hasn't properly initialized the alias mappings

The solution involves rebuilding the aliases database. Execute these commands:

sudo nano /etc/aliases  # Verify your alias mappings
sudo newaliases        # Rebuild the database
sudo service postfix restart

Ensure your /etc/aliases contains at minimum these critical entries:

# Basic system aliases
mailer-daemon: postmaster
postmaster: root
root: your-real-email@domain.com

# ZoneMinder specific
zmpkg: root
zmfilter: root
zmaudit: root

For persistent issues, check these configuration elements:

# Verify Postfix alias configuration
postconf alias_maps
postconf alias_database

# Expected output should include:
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases

If permissions are suspect, run:

sudo chmod 644 /etc/aliases
sudo chmod 644 /etc/aliases.db
sudo chown root:root /etc/aliases*
sudo postfix check

In /etc/zm/zm.conf, ensure email settings are properly configured:

ZM_EMAIL_ADDRESS=your-email@domain.com
ZM_EMAIL_SUBJECT="ZoneMinder Alarm Notification"
ZM_EMAIL_BODY="Motion detected in zone %zonename%"

Verify the fix works by sending a test email through ZoneMinder's notification system and checking mail logs:

tail -f /var/log/mail.log

You should see successful delivery messages instead of database errors.

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When working with Postfix on Ubuntu, you might encounter the frustrating error:

warning: hash:/etc/aliases is unavailable. open database /etc/aliases.db: No such file or directory

This occurs because Postfix can't find the compiled alias database, even though your main.cf configuration looks correct.

Postfix uses two key files for mail aliases:

• /etc/aliases - The human-readable text file containing alias definitions
• /etc/aliases.db - The compiled database version that Postfix actually uses

The error suggests the second file is missing or inaccessible.

Here's how to properly create the database:

sudo newaliases

Or alternatively:

sudo postalias /etc/aliases

After creating the database, check permissions:

ls -l /etc/aliases*

You should see something like:

-rw-r--r-- 1 root root 123 Apr 16 12:34 /etc/aliases
-rw-r--r-- 1 root root 4096 Apr 16 12:35 /etc/aliases.db

Ensure your main.cf contains these critical lines:

alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases

If the issue persists, try these diagnostic commands:

sudo postfix check
sudo postfix set-permissions
sudo postconf alias_maps alias_database

For production systems, consider adding this to your Postfix installation script:

# Ensure alias database exists
if [ ! -f /etc/aliases.db ]; then
    sudo newaliases
fi
# Verify permissions
sudo chmod 644 /etc/aliases.db
sudo chown root:root /etc/aliases.db

After applying changes, test with:

echo "Test message" | mail -s "Test" root
postqueue -p

You should no longer see the "alias database unavailable" error in your mail logs.