kinit

kinit is a command-line utility used in Kerberos authentication systems to obtain and cache a Ticket Granting Ticket (TGT) from the Key Distribution Center (KDC). This TGT is then used to request service tickets for accessing Kerberos-enabled services, playing a fundamental role in the Kerberos authentication process.

Purpose

• Obtain a TGT: kinit initiates the Kerberos authentication process by obtaining a Ticket Granting Ticket (TGT) for a user. The TGT proves the user's identity and allows them to request access to network services.

• Credential Caching: Once a TGT is obtained, it is stored in a local credential cache, which is used by other Kerberos utilities (like klist) to manage and display active tickets.

• Facilitates Single Sign-On (SSO): With a valid TGT, a user can access multiple Kerberos-protected services without re-entering their password, thereby enabling single sign-on.

Basic Syntax

kinit [options] [principal]

• [principal]: The Kerberos principal (usually in the form user@REALM). If omitted, kinit will prompt for a principal.

Common Options

• -V: Verbose mode; displays detailed information during the ticket acquisition process.

  kinit -V [e-mail]

• -l <lifetime>: Specifies the lifetime of the ticket (e.g., 8h, 1d). The ticket will expire after this duration.

  kinit -l 8h [e-mail]

• -r <renewable_lifetime>: Specifies a renewable lifetime for the ticket. This allows the ticket to be renewed after it expires, without needing to re-authenticate.

  kinit -r 7d [e-mail]

• -S <service>: Specifies the service for which a ticket is requested. This is used when you need a ticket for a service other than the default TGT.

  kinit -S host/server.example.com [e-mail]

• -X <option>: Passes extra options to the underlying Kerberos libraries. For example, -X X509_user_identity=FILE:/path/to/cert_and_key can be used for certificate-based authentication.

Example Usage

1. Basic TGT Acquisition: Obtain a TGT for a user. This command will prompt for the user's password.

   kinit [e-mail]

2. Verbose Mode with Specified Ticket Lifetime: Request a TGT with verbose output and a lifetime of 8 hours.

   kinit -V -l 8h [e-mail]

3. Requesting a Service Ticket: Obtain a ticket for a specific service (e.g., accessing a server).

   kinit -S host/server.example.com [e-mail]

Troubleshooting

• Ticket Not Obtained: If kinit fails to obtain a ticket, verify:

  • The principal is correctly formatted (e.g., user@REALM).

  • Network connectivity to the KDC.

  • Correct time synchronization between the client and the KDC (Kerberos is time-sensitive).

  • Proper configuration of the /etc/krb5.conf file.

• Expired Tickets: Use klist to check the validity and expiration of your tickets. If tickets are expired, run kinit again to renew them.

• Verbose Output: Run kinit with the -V flag to get detailed output that can help pinpoint where the authentication process is failing.

Conclusion

kinit is a vital tool in Kerberos environments, enabling users to obtain and cache a Ticket Granting Ticket, which underpins secure, single sign-on access to network services. By understanding its options and usage, administrators and users can effectively manage Kerberos authentication, troubleshoot issues, and ensure a smooth authentication experience across Kerberos-enabled applications.