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 a database, typically located at
           /var/lib/sss/secrets 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 a database, much like SSSD caches user or group
       entries. The database is typically located at “/var/lib/sss/secrets”.

OBTAINING DEBUG LOGS

       The sssd-kcm service is typically socket-activated systemd(1). To generate debug logs, add
       the following either to the /etc/sssd/sssd.conf file directly or as a configuration
       snippet to /etc/sssd/conf.d/ directory:

           [kcm]
           debug_level = 10

       Then, restart the sssd-kcm service:

           systemctl restart sssd-kcm.service

       Finally, run whatever use-case doesn't work for you. The KCM logs will be generated at
       /var/log/sssd/sssd_kcm.log. It is recommended to disable the debug logs when you no longer
       need the debugging to be enabled as the sssd-kcm service can generate quite a large amount
       of debugging information.

       Please note that configuration snippets are, at the moment, only processed if the main
       configuration file at /etc/sssd/sssd.conf exists at all.

CONFIGURATION OPTIONS

       The KCM service is configured in the “kcm” section of the sssd.conf file. Please note that
       because the KCM service is typically socket-activated, it is enough to just restart the
       “sssd-kcm” service after changing options in the “kcm” section of sssd.conf:

           systemctl restart sssd-kcm.service

       The KCM service is configured in the “kcm” 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

       max_ccaches (integer)
           How many credential caches does the KCM database allow for all users.

           Default: 0 (unlimited, only the per-UID quota is enforced)

       max_uid_ccaches (integer)
           How many credential caches does the KCM database allow per UID. This is equivalent to
           “with how many principals you can kinit”.

           Default: 64

       max_ccache_size (integer)
           How big can a credential cache be per ccache. Each service ticket accounts into this
           quota.

           Default: 65536

SEE ALSO

       sssd(8), sssd.conf(5),

AUTHORS

       The SSSD upstream - https://pagure.io/SSSD/sssd/