Reserved, Invalid, and Misconfigured Usernames in cPanel & WHM

1. Introduction

cPanel & WHM enforces strict rules for usernames to ensure system stability and security. This guide explains username restrictions, reserved names, special exceptions, and how to resolve issues when a username is invalid, reserved, or misconfigured.

2. Basic Username Restrictions

When creating or modifying a cPanel or WHM username, the following rules apply:

• Usernames may only contain lowercase letters (a–z) and digits (0–9).
• Usernames cannot exceed 16 characters.
• Usernames cannot begin with a digit or the string test.
• Usernames cannot end with the string assword.

3. Special Cases

• You cannot create a username containing a hyphen (-), but you may transfer an account with a hyphenated username to another system.
• To allow usernames longer than eight characters, set the following in /var/cpanel/whm/nvdata/root.yaml:

LONGUSERS: 1

• If using MySQL or PostgreSQL, the first eight characters of all usernames must be unique.

Note: You can disable database prefixing in WHM » Tweak Settings » SQL.

• To allow usernames beginning with digits, create the following file:

/etc/allowstupidstuff

• You cannot use a username that matches a group name in /etc/sudoers or /etc/sudoers.d.

4. Reserved Usernames

cPanel & WHM reserves certain usernames for system use. These cannot be used for cPanel or WHM accounts.

Important: Since TSR‑2017‑0006, email aliases in /etc/aliases and /etc/localaliases are also reserved. Any alias pointing to a reserved username is also restricted.

4.1 Files Checked for Reserved Names

• /usr/local/cpanel/Cpanel/Validate/Username/Core.pm
• /etc/aliases
• /etc/localaliases

4.2 Default Reserved Aliases

Username	Aliases
root	admin, abuse, adm, apache, bin, daemon, ftp, mail, mysql, named, nobody, postmaster, security, sshd, system, webmaster, wheel, xfs, and many more
postmaster	info, mailer-daemon, marketing, sales, support
news	newsadm, newsadmin, usenet
ftp	ftp-adm, ftp-admin, ftpadm, ftpadmin
webmaster	www

5. Resolving Username Problems

5.1 Rename an Invalid or Reserved Username

To rename an account, run the following command as root:

whmapi1 modifyacct user=username newuser=newusername

Note: Replace username with the current restricted username and newusername with the desired valid username.

5.2 Remove Username Aliases

You may remove reserved aliases from:

• /etc/aliases
• /etc/localaliases

6. Misconfigured Usernames

A misconfigured username is incomplete or missing required system data. To fix it, run:

/usr/local/cpanel/scripts/updateuserdomains --force

Conclusion

Understanding cPanel & WHM username restrictions helps prevent account creation issues and ensures system stability. When problems occur, renaming accounts or repairing misconfigurations with the appropriate commands resolves most issues quickly.