For ESXi hosts, you have to use a password with predefined requirements. You can change the required length and character class requirement or allow pass phrases using the Security.PasswordQualityControl advanced option.
ESXi uses the Linux PAM module pam_passwdqc for password management and control. See the manpage for pam_passwdqc for detailed information.
The default requirements for ESXi passwords can change from one release to the next. You can check and change the default password restrictions using the Security.PasswordQualityControl advanced option.
ESXi enforces password requirements for access from the Direct Console User Interface, the ESXi Shell, SSH, or the vSphere Client. By default, you have to include a mix of characters from four character classes: lowercase letters, uppercase letters, numbers, and special characters such as underscore or dash when you create a password.
An uppercase character that begins a password does not count toward the number of character classes used. A number that ends a password does not count toward the number of character classes used.
Passwords cannot contain a dictionary word or part of a dictionary word.
Example ESXi Passwords
The following password candidates illustrate potential passwords if the option is set as follows.
With this setting, passwords with one or two character classes and pass phases are not allowed, because the first three items are disabled. Passwords from three- and four-character classes require seven characters. See the pam_passwdqc manpage for details.
With these settings, the following passwords are allowed.
xQaTEhb!: Contains eight characters from three character classes.
xQaT3#A: Contains seven characters from four character classes.
The following password candidates do not meet requirements.
Xqat3hi: Begins with an uppercase character, reducing the effective number of character classes to two. The minimum number of required character classes is three.
xQaTEh2: Ends with a number, reducing the effective number of character classes to two. The minimum number of required character classes is three.
ESXi Pass Phrase
Instead of a password, you can also use a pass phrase; however, pass phrases are disabled by default. You can change this default or other settings, by using the Security.PasswordQualityControl advanced option from the vSphere Web Client.
For example, you can change the option to the following.
This example allows pass phrases of at least 16 characters and at least 3 words, separated by spaces.
For legacy hosts, changing the /etc/pamd/passwd file is still supported, but changing the file is deprecated for future releases. Use the Security.PasswordQualityControl advanced option instead.
Changing Default Password Restrictions
You can change the default restriction on passwords or pass phrases by using the Security.PasswordQualityControl advanced option for your ESXi host. See the vCenter Server and Host Management documentation for information on setting ESXi advanced options.
You can change the default, for example, to require a minimum of 15 characters and a minimum number of four words, as follows:
retry=3 min=disabled,disabled,15,7,7 passphrase=4
See the manpage for pam_passwdqc for details.
Not all possible combinations of the options for pam_passwdqc have been tested. Perform additional testing after you change the default password settings.
ESXi Account Lockout Behavior
Starting with vSphere 6.0, account locking is supported for access through SSH and through the vSphere Web Services SDK. The Direct Console Interface (DCUI) and the ESXi Shell do not support account lockout. By default, a maximum of ten failed attempts is allowed before the account is locked. The account is unlocked after two minutes by default.
Configuring Login Behavior
You can configure the login behavior for your ESXi host with the following advanced options:
Security.AccountLockFailures. Maximum number of failed login attempts before a user's account is locked. Zero disables account locking.
Security.AccountUnlockTime. Number of seconds that a user is locked out.
See the vCenter Server and Host Management documentation for information on setting ESXi advanced options.