Ubuntu Manpage: sssd-kcm - SSSD Kerberos Cache Manager

Provided by: sssd-kcm_1.16.1-1ubuntu1.8_amd64

NAME

       sssd-kcm - SSSD Kerberos Cache Manager

DESCRIPTION

This manual page describes the configuration of the SSSD Kerberos Cache Manager (KCM). KCM
is a process that stores, tracks and manages Kerberos credential caches. It originates in
the Heimdal Kerberos project, although the MIT Kerberos library also provides client side
(more details on that below) support for the KCM credential cache.

In a setup where Kerberos caches are managed by KCM, the Kerberos library (typically used
through an application, like e.g., kinit(1), is a “"KCM client"” and the KCM daemon is
being referred to as a “"KCM server"”. The client and server communicate over a UNIX
socket.

The KCM server keeps track of each credential caches's owner and performs access check
control based on the UID and GID of the KCM client. The root user has access to all
credential caches.

The KCM credential cache has several interesting properties:

• since the process runs in userspace, it is subject to UID namespacing, unlike the
kernel keyring

• unlike the kernel keyring-based cache, which is shared between all containers, the KCM
server is a separate process whose entry point is a UNIX socket

• the SSSD implementation stores the ccaches in the SSSD sssd-secrets(5) secrets store,
allowing the ccaches to survive KCM server restarts or machine reboots.

This allows the system to use a collection-aware credential cache, yet share the
credential cache between some or no containers by bind-mounting the socket.

USING THE KCM CREDENTIAL CACHE

       In order to use KCM credential cache, it must be selected as the default credential type
       in krb5.conf(5), The credentials cache name must be only “KCM:” without any template
       expansions. For example:

           [libdefaults]
               default_ccache_name = KCM:

       Next, make sure the Kerberos client libraries and the KCM server must agree on the UNIX
       socket path. By default, both use the same path /var/run/.heim_org.h5l.kcm-socket. To
       configure the Kerberos library, change its “kcm_socket” option which is described in the
       krb5.conf(5) manual page.

       Finally, make sure the SSSD KCM server can be contacted. The KCM service is typically
       socket-activated by systemd(1). Unlike other SSSD services, it cannot be started by adding
       the “kcm” string to the “service” directive.

           systemctl start sssd-kcm.socket
           systemctl enable sssd-kcm.socket

       Please note your distribution may already configure the units for you.

THE CREDENTIAL CACHE STORAGE

       The credential caches are stored in the SSSD secrets service (see sssd-secrets(5) for more
       details). Therefore it is important that also the sssd-secrets service is enabled and its
       socket is started:

           systemctl start sssd-secrets.socket
           systemctl enable sssd-secrets.socket

       Your distribution should already set the dependencies between the services.

CONFIGURATION OPTIONS

       The KCM service is configured in the “kcm” section of the sssd.conf file. Please note that
       currently, is it not sufficient to restart the sssd-kcm service, because the sssd
       configuration is only parsed and read to an internal configuration database by the sssd
       service. Therefore you must restart the sssd service if you change anything in the “kcm”
       section of sssd.conf. For a detailed syntax reference, refer to the “FILE FORMAT” section
       of the sssd.conf(5) manual page.

       The generic SSSD service options such as “debug_level” or “fd_limit” are accepted by the
       kcm service. Please refer to the sssd.conf(5) manual page for a complete list. In
       addition, there are some KCM-specific options as well.

       socket_path (string)
           The socket the KCM service will listen on.

           Default: /var/run/.heim_org.h5l.kcm-socket

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