pamkrb5so

pamkrb5so is a PAM (Pluggable Authentication Module) commonly used to perform Kerberos 5 authentication on Unix-like systems. It enables applications such as login, su, and sudo to authenticate users against a Kerberos realm by leveraging the Kerberos protocol and client libraries.

In operation, pamkrb5so interacts with the Kerberos Key Distribution Center (KDC) to verify a user’s password and to obtain Kerberos credentials, typically a Ticket Granting Ticket (TGT). Once credentials are obtained, they are stored in the Kerberos credential cache (often referenced by the KRB5CCNAME environment variable) for use in subsequent authentication and service tickets. The module can be configured to reuse passwords supplied earlier in the PAM stack and to control how long credentials remain valid.

Configuration of pamkrb5so occurs through PAM stack files, such as those in /etc/pam.d, where the module is invoked at appropriate stages of authentication. Typical options influence behavior such as whether to prompt for a password, reuse an existing password, or request a TGT only when necessary. Depending on the Kerberos client implementation (MIT Kerberos or Heimdal) and distribution packaging, the binary may be named pamkrb5so or provided as pam_krb5.so; options and syntax can vary slightly between implementations.

Security considerations include the secure handling and storage of credentials, proper management of the credential cache, and ensuring the Kerberos configuration (krb5.conf) and key distribution processes are protected. Misconfigurations can lead to credential leakage or authentication failures. pamkrb5so is part of the broader Kerberos authentication ecosystem and is often used in environments that rely on centralized, time-synchronized credentials and single sign-on capabilities.

See also Kerberos, PAM, pam_krb5.so, MIT Kerberos, Heimdal.