When manually migrating local accounts to OpenLDAP, what is the most likely cause of an invalid credentials error during authentication?

An invalid credentials error during authentication when migrating local accounts to OpenLDAP is most likely caused by the fact that the password hash type was not included in the user's password attribute. OpenLDAP expects passwords to be stored in a specific format that includes not just the hashed password, but also the identifier of the hashing algorithm used, such as {SSHA} for salted SHA-1 hashes or {MD5} for MD5 hashes. If this identifier is missing, OpenLDAP cannot properly interpret the hash and consequently cannot verify the provided password against what is stored, leading to authentication failure.

In contrast, shadow passwords being incompatible with OpenLDAP is not a primary cause of invalid credentials, as OpenLDAP can handle various password storage schemes provided they are converted properly. Similarly, the original password from /etc/passwd being unavailable is not a direct issue when the password hashes are involved, since the hashes, once correctly formatted, should suffice for authentication. Lastly, neglecting to run the slappasswd command to convert the hashes from /etc/shadow would also lead to authentication issues but is more about the conversion step than how hashes are interpreted at the time of authentication. Therefore, having the correct hash type included is crucial for successful verification of credentials in OpenLDAP.