Administrative user accounts have been defined on the remote LDAP server and are unable to...

When BIG-IP is configured to use remote authentication (such as LDAP), all authentication and authorization attempts—including successes and failures—are logged to /var/log/secure.

For LDAP-based administrative login issues, /var/log/secure contains:

LDAP authentication failures

PAM authentication errors

Authorization and access-denied messages

Details explaining why a remote user could not log in

Why the other options are incorrect:

/var/log/user.log is not a standard BIG-IP log file for authentication.

/var/log/ltm logs traffic management events, not user authentication.

/var/log/messages contains general system messages but not detailed authentication failure information.

Therefore, the correct log file to troubleshoot LDAP administrative login failures is /var/log/secure.

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