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 lslebodn@redhat.com Sent: 18 June 2020 12:04 To: End-user discussions about the System Security Services Daemon sssd-users@lists.fedorahosted.org 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, ...

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