PAM_SSS(8)

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👑 PAM_SSS(8) — the SSSD manual page, but make it make sense ✨

okay bestie, so this is pam_sss(8) from the SSSD Manual pages and honestly? it's kind of the main character of the whole auth stack. sit down, grab a matcha 🍓, and let's get into it.

🌸 NAME 🌸

pam_sss — the PAM module for SSSD, no cap 💅

✨ SYNOPSIS ✨

pam_sss.so [quiet] [forward_pass] [use_first_pass] [use_authtok]
           [retry=N] [ignore_unknown_user] [ignore_authinfo_unavail]
           [domains=X] [allow_missing_name] [prompt_always]
           [try_cert_auth] [require_cert_auth] [allow_chauthtok_by_root]

🦋 DESCRIPTION 🦋

So pam_sss.so is literally the PAM interface to the System Security Services daemon (SSSD, iykyk). Like, PAM talks, SSSD listens, everyone's authenticated 🫶.

Errors and results? They get logged through syslog(3) with the LOG_AUTHPRIV facility. That's it, that's the vibe.

🎀 OPTIONS 🎀

  • quiet — shhh 🤫. Suppresses log messages for unknown users. Not me making your logs quiet for the mystery-user situation.
  • forward_pass — if forward_pass is set, the entered password gets put on the stack so other PAM modules can use it. Sharing is caring, periodt.
  • use_first_pass — this argument literally forces the module to use a previously stacked module's password and it will never prompt the user. And if no password is available or the password isn't appropriate? user gets denied access. harsh but fair 💀.
  • use_authtok — when password changing, this enforces that the module sets the new password to the one provided by a previously stacked password module. teamwork, bestie 🫶.
  • retry=N — if specified, the user gets asked another N times for a password if authentication fails. Default is 0.
ok lowkey important: this option might not work as expected if the application calling PAM handles the user dialog on its own. A typical example is sshd with PasswordAuthentication. so like… don't come for pam_sss when sshd ate your retries 🙈.
  • ignore_unknown_user — if this is specified and the user does not exist, the PAM module returns PAM_IGNORE. That makes the PAM framework ignore this module. bye bestie 👋.
  • ignore_authinfo_unavail — says the PAM module should return PAM_IGNORE if it can't contact the SSSD daemon. Again, PAM framework then ignores this module. it's giving "if you can't reach me, don't worry about me" ✨.
  • domains — lets the administrator restrict which domains a particular PAM service is allowed to authenticate against. Format is a comma-separated list of SSSD domain names, as specified in the sssd.conf file.
NOTE: if this is used for a service not running as root user — e.g. a web-server — it must be used in conjunction with the pam_trusted_users and pam_public_domains options. Please see the sssd.conf(5) manual page for more info on these two PAM responder options. this is not a drill 🔥.
  • allow_missing_name — the main purpose of this option is to let SSSD determine the user name based on additional information, e.g. the certificate from a Smartcard 🎫.

The current use case are login managers which can monitor a Smartcard reader for card events. In case a Smartcard is inserted, the login manager will call a PAM stack which includes a line like

auth sufficient pam_sss.so allow_missing_name

In this case SSSD will try to determine the user name based on the content of the Smartcard, returns it to pam_sss which will finally put it on the PAM stack. iconic behavior honestly 👑.

  • prompt_always — always prompt the user for credentials. With this option, credentials requested by other PAM modules — typically a password — will be ignored and pam_sss will prompt for credentials again. Based on the pre-auth reply by SSSD, pam_sss might prompt for a password, a Smartcard PIN or other credentials. like it's not gonna take anyone else's word for it 💅.
  • try_cert_auth — try to use certificate based authentication, i.e. authentication with a Smartcard or similar devices. If a Smartcard is available and the service is allowed for Smartcard authentication, the user will be prompted for a PIN and the certificate based authentication will continue ✨.

If no Smartcard is available or certificate based authentication is not allowed for the current service, PAM_AUTHINFO_UNAVAIL is returned.

  • require_cert_auth — do certificate based authentication, i.e. authentication with a Smartcard or similar devices. If a Smartcard is not available the user will be prompted to insert one 🎫. SSSD will wait for a Smartcard until the timeout defined by p11_wait_for_card_timeout passed — please see sssd.conf(5) for details.

If no Smartcard is available after the timeout, or certificate based authentication is not allowed for the current service, PAM_AUTHINFO_UNAVAIL is returned.

  • allow_chauthtok_by_root — by default, the chauthtok PAM action will short-circuit to returning PAM_SUCCESS when pam_sss.so is invoked by root user 😭. This option disables that behavior, allowing you to change auth tokens when running as root. root gets to actually do the thing now 🫶.

🌈 MODULE TYPES PROVIDED 🌈

All module types — account, auth, password and session — are provided. every single one. slay 💅.

If SSSD's PAM responder is not running — e.g. if the PAM responder socket is not available — pam_sss will return PAM_USER_UNKNOWN when called as account module, to avoid issues with users from other sources during access control. it's giving considerate 🧚.

💜 RETURN VALUES 💜

  • PAM_SUCCESS — the PAM operation finished successfully. we love a happy ending ✨.
  • PAM_USER_UNKNOWN — the user is not known to the authentication service, or the SSSD's PAM responder is not running. mystery user fr.
  • PAM_AUTH_ERR — authentication failure. Also, could be returned when there is a problem with getting the certificate. 💀.
  • PAM_PERM_DENIED — permission denied. The SSSD log files may contain additional information about the error. check the logs bestie 🙈.
  • PAM_IGNORE — see options ignore_unknown_user and ignore_authinfo_unavail. told you it was a whole thing.
  • PAM_AUTHTOK_ERR — unable to obtain the new authentication token. Also, could be returned when the user authenticates with certificates and multiple certificates are available, but the installed version of GDM does not support selection from multiple certificates. GDM catching strays 😭.
  • PAM_AUTHINFO_UNAVAIL — unable to access the authentication information. This might be due to a network or hardware failure 🔌.
  • PAM_BUF_ERR — a memory error occurred. Also, could be returned when options use_first_pass or use_authtok were set, but no password was found from the previously stacked PAM module. the stack was empty, it's giving awkward 🫠.
  • PAM_SYSTEM_ERR — a system error occurred. The SSSD log files may contain additional information about the error.
  • PAM_CRED_ERR — unable to set the credentials of the user.
  • PAM_CRED_INSUFFICIENT — the application does not have sufficient credentials to authenticate the user. For example, missing PIN during smartcard authentication or missing factor during two-factor authentication. one factor is not enough, we need the whole fit 👑.
  • PAM_SERVICE_ERR — error in service module.
  • PAM_NEW_AUTHTOK_REQD — the user's authentication token has expired. time for a new one ⏰.
  • PAM_ACCT_EXPIRED — the user account has expired.
  • PAM_SESSION_ERR — unable to fetch IPA Desktop Profile rules or user info.
  • PAM_CRED_UNAVAIL — unable to retrieve Kerberos user credentials.
  • PAM_NO_MODULE_DATA — no authentication method was found by Kerberos. This might happen if the user has a Smartcard assigned but the pkint plugin is not available on the client. (yes, pkint, exactly like that, we don't edit the source 🫶)
  • PAM_CONV_ERR — conversation failure. the chat did not go well 💀.
  • PAM_AUTHTOK_LOCK_BUSY — no KDC suitable for password change is available.
  • PAM_ABORT — unknown PAM call.
  • PAM_MODULE_UNKNOWN — unsupported PAM task or command.
  • PAM_BAD_ITEM — the authentication module cannot handle Smartcard credentials. it said no thank you 🙈.

🍓 FILES 🍓

If a password reset by root fails because the corresponding SSSD provider does not support password resets, an individual message can be displayed. This message can e.g. contain instructions about how to reset a password 📝.

The message is read from the file pam_sss_pw_reset_message.LOC where LOC stands for a locale string returned by setlocale(3). If there is no matching file, the content of pam_sss_pw_reset_message.txt is displayed.

security check bestie 🔐: root must be the owner of the files, and only root may have read and write permissions, while all other users must have only read permissions.

These files are searched in the directory /etc/sssd/customize/DOMAIN_NAME/. If no matching file is present, a generic message is displayed. fallback queen behavior 💅.

🔥 SEE ALSO 🔥

sssd(8), sssd.conf(5), sssd-ldap(5), sssd-ldap-attributes(5), sssd-krb5(5), sssd-simple(5), sssd-ipa(5), sssd-ad(5), sssd-idp(5), sssd-sudo(5), sssd-session-recording(5), sss_cache(8), sss_debuglevel(8), sss_obfuscate(8), sss_seed(8), sssd_krb5_locator_plugin(8), sss_ssh_authorizedkeys(1), sss_ssh_knownhosts(1), sssd-ifp(5), pam_sss(8), sss_rpcidmapd(5)

(yes that's a lot of reading. go off, you've got this 🌈)

⭐ AUTHORS ⭐

The SSSD upstream — https://github.com/SSSD/sssd/

and that's the whole page bestie 🎀 — brought to you by SSSD, dated 06/09/2026, under the name PAM_SSS(8). go forth and authenticate responsibly, ily 💖✨🦋

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