SSSD Manual pages
sssd-kcm
8
File Formats and Conventions
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.,
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 the SSSD
sssd-secrets5
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.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 CACHE STORAGE
The credential caches are stored in the SSSD secrets service (see
sssd-secrets5
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
SEE ALSO
sssd8
,
sssd.conf5
,