Messaging is configured by default to support only local host accounts. A local host account is an account in which all authentication, authorization, and accounting information is maintained on the same server to which the user is attempting access.
To avoid lockout to the system, you can administer at least one local host account on Messaging so that the server is accessible when access to an external Authentication, Authorization, and Auditing (AAA) server is blocked for any reason. Local host accounts can be used at the same time as any of the external AAA services. The local host configuration on Messaging uses the /etc/passwd, /etc/shadow, and /etc/group files, among others.