ubuntu hostname长度限制

Ubuntu Hostname Length Limit
The maximum length of a hostname in Ubuntu is 63 characters by default, a limit imposed by the Linux kernel to ensure compatibility with DNS (Domain Name System) and other network protocols. This constraint applies to most modern Ubuntu releases (e.g., 20.04, 22.04, 23.10) and is consistent across Debian-based distributions.

Key Details About the Length Limit

• Technical Boundary: The 63-character limit originates from the kernel’s kernel.hostname parameter, which enforces this rule to prevent overly long hostnames from causing issues in network communication (e.g., DNS resolution failures or truncated entries in system logs).
• Practical Enforcement: If you attempt to set a hostname exceeding 63 characters (e.g., via sudo hostnamectl set-hostname very-long-hostname-that-exceeds-the-limit), Ubuntu will automatically truncate the name to 63 characters. This truncation can lead to unexpected behavior (e.g., services failing to recognize the hostname) if not addressed.
• Modification (Not Recommended): While it’s possible to increase the limit by editing the /etc/sysctl.conf file (adding kernel.hostname = new-hostname) and running sudo sysctl -p to apply changes, this is not advised. Longer hostnames can reduce readability, complicate troubleshooting, and may not be supported by all network devices or applications.

Additional Naming Rules to Complement Length Limits

To avoid conflicts and ensure usability, follow these complementary guidelines when setting a hostname:

• Character Set: Use only lowercase letters (a-z), numbers (0-9), and hyphens (-). Avoid spaces, special symbols (!, @, #, $, etc.), or underscores (_).
• Structure: Hyphens cannot be the first or last character of a hostname (e.g., -myhost or myhost- is invalid). Do not use consecutive hyphens (e.g., my--host).
• Uniqueness: Ensure the hostname is unique within your local network to prevent DNS or network service conflicts.
• Reserved Words: Avoid using system reserved keywords like localhost, root, or admin as hostnames, as they can interfere with system operations.

By adhering to these rules—including the 63-character length limit—you can maintain a functional, secure, and manageable hostname for your Ubuntu system.