As a Linux system administrator working with mixed environments, I've often found myself caught between two different schools of thought regarding hostname configuration. The Red Hat/CentOS camp advocates for using Fully Qualified Domain Names (FQDNs) in the /etc/sysconfig/network file:

# RHEL/CentOS style
HOSTNAME=server01.example.com

Meanwhile, Debian/Ubuntu systems explicitly recommend against FQDNs in /etc/hostname:

# Debian/Ubuntu style
server01

This divergence becomes particularly important when dealing with automation tools and monitoring systems. For example, Nagios might behave differently depending on how the hostname is set:

# Bash script checking hostname type
if [[ $(hostname) == *.* ]]; then
    echo "FQDN detected - compatible with RHEL-based monitoring"
else
    echo "Short name detected - may require configuration adjustments"
fi

When managing mixed environments, I recommend choosing one approach and applying it consistently. Here's a Puppet manifest snippet that enforces consistency:

# Puppet code to standardize hostnames
case $::osfamily {
    'RedHat': {
        file_line { 'set FQDN hostname':
            path => '/etc/sysconfig/network',
            line => "HOSTNAME=${::fqdn}",
        }
    }
    'Debian': {
        file { '/etc/hostname':
            content => "${::hostname}\n",
        }
    }
}
exec { 'apply hostname':
    command => "/bin/hostname ${::hostname}",
}

Some enterprise software has specific requirements:

• Oracle RAC: Prefers FQDNs for node identification
• IBM Tivoli: Some components require short names
• Kubernetes: Uses FQDNs for node registration

For most modern environments, I suggest using FQDNs as they provide clearer identification in distributed systems. Here's how to convert a short name to FQDN in a script:

#!/bin/bash
# Ensure FQDN is set
SHORT_NAME=$(hostname -s)
DOMAIN=$(dnsdomainname)
FQDN="${SHORT_NAME}.${DOMAIN}"

# Apply to RHEL systems
if [ -f /etc/redhat-release ]; then
    sed -i "s/HOSTNAME=.*/HOSTNAME=${FQDN}/" /etc/sysconfig/network
    hostname "$FQDN"
fi

In Linux system administration, one of the most persistent debates revolves around whether to configure the system hostname as a Fully Qualified Domain Name (FQDN) or just the short hostname. Major distributions like Red Hat/CentOS and Debian/Ubuntu have fundamentally different recommendations:

# Red Hat/CentOS style (typically in /etc/sysconfig/network)
HOSTNAME=server1.example.com

# Debian/Ubuntu style (in /etc/hostname)
server1

Red Hat/CentOS: Explicitly recommends using FQDN in their documentation. The /etc/sysconfig/network file expects the full domain name.

Debian/Ubuntu: The /etc/hostname file should contain only the short hostname, with the domain configured separately in /etc/hosts or via DHCP.

Several system components behave differently based on hostname configuration:

• Postfix: Uses the system hostname for HELO/EHLO unless explicitly configured
• Apache: ServerName directive may inherit from system hostname
• SSH: Host keys are stored using the reported hostname

For mixed environments, I recommend this hybrid approach:

# /etc/hostname (short name)
server1

# /etc/hosts configuration
127.0.0.1   localhost
192.168.1.10 server1.example.com server1

# Additional configuration for Red Hat systems
if [ -f /etc/sysconfig/network ]; then
    echo "HOSTNAME=server1.example.com" >> /etc/sysconfig/network
fi

These commands help manage hostnames consistently:

# Set transient hostname (until reboot)
hostnamectl set-hostname server1

# Set pretty hostname (for display purposes)
hostnamectl set-hostname --pretty "Production Web Server"

# View current settings
hostnamectl status

When hostname configuration causes problems:

1. Check what hostname -f returns (should be FQDN)
2. Verify getent hosts $(hostname) resolves correctly
3. Ensure reverse DNS matches forward DNS

The most robust approach is to configure both short name and FQDN properly in all relevant locations, then test all critical services.