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After a fresh install and update && upgrade, I have followed this guide to add the machine to our AD infrastructure, but after basic configuration realm join -v [domain] returns

! Can't contact LDAP server

realm: No such realm found

So I fired up a CentOS minimal VM and was able to register the machine through that. Cross-referencing the two outputs, I noticed that on Ubuntu the same realm command is querying the wrong IP when looking up the LDAP server, but I did not find any info on how to change that parameter in config files or through man realm.

So I tried ldapsearch -h [server IP], manually specifying the server and this was returned:

ldap_sasl_interactive_bind_s: Local error (-2)

    additional info: SASL(-1): generic failure: GSSAPI Error: Unspecified GSS failure.  Minor code may provide more information (No Kerberos credentials available (default cache: FILE:/tmp/krb5cc_0))

which it should not be an issue since the same result is given by the CentOS VM, despite it joining successfully. So, I copied over from the CentOS machine the config files for krb5.conf, sssd.conf and realmd.conf (after a backup), but the same original error was given.

I believe that the wrong LDAP DSE lookup is the issue but I cannot find the parameter to change anywhere.

Thank you for all your help.

The AD server runs Windows Server 2016.
Providing .conf files below:

krb5.conf

[libdefaults]

    default_realm = MYDOMAIN.COM

    dns_lookup_realm = true

    dns_lookup_kdc = true

    forwardable = true

    rdns = false    



[realms]

    MYDOMAIN.COM = {

                kdc = server.mydomain.com

                admin_server = server.mydomain.com

                default_domain = mydomain.com

    }



[domain_realm]

    .mydomain.com = MYDOMAIN.COM

    mydomain.com = MYDOMAIN.COM

sssd.conf

[sssd]

services = nss, pam

domains = mydomain.com

config_file_version = 2





[domain/mydomain.com]

id_provider = ad

access_provider = ad

ad_domain = mydomain.com

krb5_realm = MYDOMAIN.COM

realmd_tags = manages-system joined-with-adcli

cache_credentials = True

krb5_store_password_if_offline = True

default_shell = /bin/bash

ldap_id_mapping = True

use_fully_qualified_names = True

fallback_homedir = /home/%d/%u

realmd.conf

[users]

    default-home = /home/%D/%U

    default-shell = /bin/bash



[active-directory]

    default-client = sssd

    os-name = Ubuntu

    os-version = 18.04



[service]

    automatic-install = no



[mydomain.com]

    fully-qualified-names = yes

    automatic-id-mapping = no

    user-principal = yes

    manage-system = yes