kerberos

kinit [options] [principal]

-f
    Forwardable: Requests a forwardable ticket, allowing it to be forwarded to other hosts.

-F
    Not forwardable: Requests a non-forwardable ticket, preventing it from being forwarded.

-p
    Proxiable: Requests a proxiable ticket, allowing it to be delegated to a proxy server.

-P
    Not proxiable: Requests a non-proxiable ticket, preventing it from being delegated.

-r
    Renewable: Requests a renewable ticket, allowing it to be renewed before expiry without re-entering password (up to maximum renewable lifetime).

-R
    Renew: Attempts to renew an existing renewable ticket without prompting for a password.

-l lifetime
    Lifetime: Specifies the desired lifetime of the ticket in a format like '5m', '4h', '3d'. The KDC may grant a shorter lifetime.

-c ccache_name
    Credential cache: Specifies the path to the credential cache file to use. Defaults to KRB5CCNAME environment variable or a system default.

-k
    Keytab: Obtains a ticket using a keytab file instead of a password.

-t keytab_file
    Keytab file: Specifies the path to the keytab file when using the -k option. Defaults to /etc/krb5.keytab or ~/krb5.keytab.

-V
    Version: Displays the Kerberos library version information and exits.

-A
    Anonymous: Requests an anonymous ticket, typically for unauthenticated access or for specific realm trust scenarios.

-S service_principal
    Service principal: Requests a ticket for a specific service principal directly, rather than a TGT.

The kinit command is a fundamental client utility for interacting with the Kerberos authentication system. It is used to obtain or renew a Kerberos ticket-granting ticket (TGT) and store it in a credential cache. A TGT is essential for subsequent authentication to Kerberos-aware services without re-entering a password.

When kinit is invoked, it typically prompts the user for their Kerberos principal's password, communicates with the Kerberos Key Distribution Center (KDC), and, upon successful authentication, issues a TGT. This TGT can then be used by other Kerberos client applications to request service tickets for specific services.

kinit plays a crucial role in establishing a user's authenticated session within a Kerberos realm, enabling secure access to networked resources like file shares, SSH, and web applications. It also supports obtaining tickets using keytab files for automated processes.

Network Connectivity: kinit requires network access to the configured Kerberos Key Distribution Center (KDC). If the KDC is unreachable or the network is down, ticket acquisition will fail.

Time Synchronization: Kerberos is highly sensitive to time synchronization. Significant clock skew between the client and the KDC can lead to authentication failures. Ensure your system's time is synchronized, e.g., via NTP.

Credential Cache Security: The credential cache file contains sensitive authentication information (the TGT). It should be protected with appropriate file permissions to prevent unauthorized access. Misconfigured permissions can lead to security vulnerabilities.

Keytab File Security: When using keytab files (with -k or -t), ensure the keytab file itself is securely stored and has restricted permissions, as it contains cryptographic keys equivalent to a password.

Password Entry: When prompted for a password, characters will not be echoed to the console for security reasons.

The term 'Kerberos command' often refers to a suite of client utilities for interacting with a Kerberos environment, rather than a single command named 'kerberos'. Key commands in this suite include kinit (for obtaining tickets), klist (for listing tickets), kdestroy (for destroying tickets), and kpasswd (for changing passwords). These commands work together to manage a user's Kerberos authentication lifecycle.

The credential cache (often referred to as 'ccache') is a temporary storage location where kinit stores the obtained Ticket-Granting Ticket (TGT) and subsequent service tickets. This allows applications and other Kerberos commands to access the user's credentials without repeatedly asking for a password. The location of the ccache is typically determined by the KRB5CCNAME environment variable, defaulting to a file in /tmp (e.g., /tmp/krb5cc_UID) or a file specified by the configuration. It is crucial to manage and protect the ccache as it represents your authenticated session.

Kerberos is a network authentication protocol that works on the basis of tickets to allow nodes communicating over a non-secure network to prove their identity to one another in a secure manner. It was developed at MIT as part of Project Athena in the 1980s. The name "Kerberos" is derived from the Greek mythological three-headed dog, Cerberus, guardian of the underworld, symbolizing its role as a network security guardian.

The initial implementations were proprietary, but MIT later released Kerberos V5 (Version 5) under a free software license, making it widely adopted. The client utilities like kinit, klist, and kdestroy are part of the standard Kerberos client package, which has been consistently maintained and evolved alongside the protocol to support new features and security enhancements. Its core functionality and usage remain largely consistent across various Unix-like operating systems, including Linux.

klist(1), kdestroy(1), kpasswd(1), krb5.conf(5), kadmin(8)