sssd-kcm 8 File Formats and Conventions sssd-kcm SSSD Kerberos Cache Manager 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., kinit1 , 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. The KCM default client idle timeout is 5 minutes, this allows more time for user interaction with command line tools such as kinit. In order to use KCM credential cache, it must be selected as the default credential type in krb5.conf5 , 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.conf5 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 caches are stored in a database, much like SSSD caches user or group entries. The database is typically located at /var/lib/sss/secrets. 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. The sssd-kcm service can be configured to attempt TGT renewal for renewable TGTs stored in the KCM ccache. Renewals are only attempted when half of the ticket lifetime has been reached. KCM Renewals are configured when the following options are set in the [kcm] section: tgt_renewal = true krb5_renew_interval = 60m SSSD can also inherit krb5 options for renewals from an existing domain. tgt_renewal = true tgt_renewal_inherit = domain-name The following krb5 options can be configured in the [kcm] section to control renewal behavior, these options are described in detail below krb5_renew_interval krb5_renewable_lifetime krb5_lifetime krb5_validate krb5_canonicalize krb5_auth_timeout 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 Note: on platforms where systemd is supported, the socket path is overwritten by the one defined in the sssd-kcm.socket unit file. 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 tgt_renewal (bool) Enables TGT renewals functionality. Default: False (Automatic renewals disabled) tgt_renewal_inherit (string) Domain to inherit krb5_* options from, for use with TGT renewals. Default: NULL sssd8 , sssd.conf5 ,