Hello,

My difficult lies with being able to debug this. The need to leave the debug on 
for ~3-4 days on a production system, is something that I would not be 
comfortable doing.

We are using Active Directory, Domain/Functional forest level Windows Server 
2012 R2.

We are in the midst of switching us stuff to be the AD provider but this is 
still KRB5/LDAP.

[sssd]
config_file_version = 2
domains = DOMAIN
services = nss, pam
 [domain/DOMAIN]
ldap_referrals = false
cache_credentials = true
enumerate = false
id_provider = ldap
auth_provider = krb5
ldap_uri = ldap://LDAP1.DOMAIN, ldap://LDAP2.DOMAIN
ldap_sasl_mech = GSSAPI
ldap_sasl_authid = SERVER$@DOMAIN
ldap_schema = rfc2307bis
ldap_user_search_base = DC=DOMAIN,DC=BASE
ldap_user_object_class = user
ldap_group_search_base = DC=DOMAIN,DC=BASE
ldap_group_object_class = group
ldap_account_expire_policy = ad
ldap_force_upper_case_realm = true
krb5_server = LDAP1.DOMAIN, LDAP2.DOMAIN
krb5_realm = DOMAIN
krb5_canonicalize = false
ldap_user_home_directory = unixHomeDirectory
ldap_user_name = sAMAccountName
ldap_user_principal = None
access_provider = simple
simple_allow_groups = USERS_GROUP

I re-joined the machine to the domain to ensure that wasn't the source of 
issues.

If there is an appropriate debug level which wouldn't be negative to a 
production system, I can try that out.

Cheers
Mark


-----Original Message-----
From: Lukas Slebodnik <[email protected]>
Sent: 18 June 2020 12:04
To: End-user discussions about the System Security Services Daemon 
<[email protected]>
Subject: [SSSD-users] Re: SSH user fails system error 4

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On (18/06/20 09:11), Sangster, Mark wrote:
>Hello,
>
>We are experiencing an issue with a user when they attempt to login. Other 
>users can continue to login. It does seem to repeat on this specific user.
>
>If I blitz the SSSD cache and restart it, then they find they can login again.
>
>They indicated that just prior to the event, they were forced to reboot their 
>machine (i.e. unclean disconnect) and it was after that they couldn’t login.
>
>This was the successful session just before:
>
>Jun 17 08:00:58 server sshd[11882]: pam_sss(sshd:auth): authentication
>success; logname= uid=0 euid=0 tty=ssh ruser= rhost=<CLIENTIP>
>user=username Jun 17 08:00:58 server sshd[11882]: Accepted password for
>username from <CLIENTIP> port 59680 ssh2 Jun 17 08:00:59 server
>sshd[11882]: pam_unix(sshd:session): session opened for user username
>by (uid=0) Jun 17 13:22:17 server sshd[11882]: pam_unix(sshd:session):
>session closed for user username
>
>The next session which failed:
>
>Jun 17 13:33:13 server sshd[13210]: pam_sss(sshd:auth): authentication
>success; logname= uid=0 euid=0 tty=ssh ruser= rhost=<CLIENTIP>
>user=username Jun 17 13:33:13 server sshd[13210]:
>pam_sss(sshd:account): Access denied for user username: 4 (System
>error) Jun 17 13:33:13 server sshd[13210]: Failed password for username
>from <CLIENTIP> port 50114 ssh2 Jun 17 13:33:13 server sshd[13210]:
>fatal: Access denied for user username by PAM account configuration
>[preauth]
>
>There does not look to be any additional log information in SSSD representing 
>the error. The troubleshooting suggested I follow up here for “system error 4”.
>
>It would be tricky to run debug on this, as this took 4 days until the failure 
>reappeared and we might fill our log space very quickly.
>

Pam return code 4 (System error) means some unexpected situation in sssd 
(usually in backend)

I would recomment to follow following guide 
https://sssd.io/docs/users/troubleshooting.html

It would be good to also provide more details about your configuration 
type/version of directory server, ...

LS
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