Understanding Hostnames in Linux

Static, Transient, and Pretty Hostnames: What’s the Difference?

• This is the permanent identifier assigned to the system. It’s stored in "/etc/hostname" and remains unchanged unless explicitly modified. Think of it as the system’s legal name—a constant that helps with consistent network identification.

• This is the kernel's temporary identifier. It might vary depending on dynamic circumstances, such as several network connections. Helpful for mobile devices connecting to several Wi-Fi networks or for transient network changes. When implementing procedures to change the hostname of Linux Ubuntu and Linux Red Hat, the transient hostname may also need adjustment.

• This allows spaces and special characters, making for a human-friendly version. It's purely cosmetic, for use in GUIs or dashboards, and has no effect on networking. For example, a pretty hostname could be “Daito’s Laptop” instead of the static daito-laptop.

How They Interact:

• When you update the static hostname, the transient hostname often adjusts to match, but they can be configured independently.
• The pretty hostname is entirely separate—useful for user interfaces but irrelevant for system operations.

Hostname Conventions: Naming Best Practices

• Hostnames can only contain letters (a-z), digits (0-9), and hyphens (-).
• They must start and end with a letter or digit—no special characters or underscores.
• Maximum length is 63 characters.

• Be Descriptive: Include the function (e.g., web-server-01), location (nyc-database), or department (finance-backup).
• Avoid Conflicts: Ensure unique names to prevent network confusion.
• Stay Consistent: Adopt a naming scheme that’s logical and easy to understand at a glance.
• Prioritize Readability: Keep it simple and easy to remember, especially for transient hostnames that may change frequently.

Checking Your Current Hostname

1. Using hostname and hostnamectl Commands

• The quickest way to check your current hostname is by running:

• This command displays the current hostname as a single string, e.g., server01.
• It’s straightforward but limited—it only shows the static hostname without additional details.

• For more comprehensive information, use:

• Example output:

2. Viewing /etc/hostname and /etc/hosts Files

• This file stores the static hostname. To view it, run:

• You’ll see a single line with the current hostname, e.g., server01.
• If you plan to change the hostname manually, this is the file to edit.

• This file maps hostnames to IP addresses. Check it with:

• A typical entry might look like this:

• If you change the hostname, you must update this file to reflect the new name, preventing network conflicts and ensuring proper system identification.

3. Understanding the Output

• If they don’t match, the system may have been reconfigured or is dynamically assigning hostnames.

• Purely cosmetic, but useful for identifying devices in GUIs or user interfaces.

• Ensures network services correctly associate the hostname with the local IP address.

Methods to Change Hostname in Linux

a. Using hostnamectl (Systemd-Based Systems)

• This displays the current static, transient, and pretty hostnames.

• Replace new-hostname with the desired name (e.g., web-server-01).
• This command updates the static hostname.

• The output should now reflect the new static, transient, and pretty hostnames.

• Unified command for managing all hostname types.
• Automatically updates necessary system files (/etc/hostname and /etc/hosts).
• Consistent across most systemd-based Linux distributions.
• Prevents accidental mismatches between hostname types.

b. Editing Configuration Files Directly

• Open the file using your preferred text editor:

• Replace the existing hostname with the new one. Example:

• Save and exit (CTRL + X, then Y, then Enter).

• Open the /etc/hosts file:

• Locate the line containing the old hostname and update it:

• Save and exit the file.

• Reboot the system to apply the new hostname:

• Once the system is back online, verify the changes:

• Ensure consistency across all outputs.

c. Using nmtui (Network Manager Text User Interface)

• This opens a graphical menu within the terminal.

• Select Set System Hostname and press Enter.
• Enter the new hostname (e.g., db-server-01).
• Confirm and exit the interface.

• Restart the NetworkManager to apply the changes:

• Verify the hostname:

d. Using nmcli (Command-Line Interface for Network Manager)

• Replace new-hostname with the desired hostname.

• This command confirms the new hostname has been applied.

e. Temporary Hostname Change with hostname Command

• The change takes effect immediately but will not persist after a reboot.

• Temporary changes do not update /etc/hostname or /etc/hosts.
• Rebooting the system will revert to the previous hostname.
• This method is ideal for testing purposes but not recommended for permanent changes.

Distribution-Specific Instructions

a. Ubuntu/Debian

• The quickest way to update the hostname:

• To set a pretty hostname (optional):

• Verify changes:

• Open the /etc/hostname file:

• Replace the old hostname with new-hostname.
• Update /etc/hosts to reflect the new hostname:

• Change the relevant line:

• Reboot the system to apply changes:

• On Ubuntu Desktop, open Settings > About and click Device Name to update the hostname.
• Alternatively, use GNOME Tweaks for a graphical interface to set the pretty hostname.

b. CentOS/RHEL/Fedora

c. Arch Linux

• Arch Linux often requires additional configuration in networking scripts and init systems, especially when using custom network managers.
• Ensure that any network services or daemons are restarted after hostname changes to prevent conflicts.

d. SUSE/OpenSUSE

Automating Hostname Changes with Scripts

1. Sample Bash Script for Changing Hostname

• Tools like Ansible, Puppet, and Chef can automate hostname changes alongside other configuration tasks.
• Example with Ansible Playbook:

Conclusion