This section contains information that is referenced from other sections, and that does not really need to be read in sequence.
4.1. Special terms¶
This documentation uses a few special terms to refer to Python types:
- The name of the protocol that pywbemcli uses to communicate with WBEM servers. CIM-XML is defined in DSP0200.
- CIM object output formats
- Pywbemcli output formats (specified with the --output-format general option) that format the resulting CIM objects or CIM object paths as MOF, CIM-XML, or using the pywbem repr or str formatting. See CIM object formats for details.
- Table output formats
- Pywbemcli output formats (specified with the --output-format general option) that format the result as a table. See Table formats for details.
- Tree output format
- A pywbemcli output format (specified with the --output-format general option) that formats the result as a tree using ASCII characters. See ASCII tree format for details.
A CIM instance path in a format that is suitable as a command line argument or option value of pywbemcli. Several commands of the instance command group use INSTANCENAME as a command line argument.
CIM_RegisteredProfile.InstanceID="acme:1" CIM_System.CreationClassName="ACME_System",Name="MySystem" CIM_System.?
- connection id
- A string that uniquely identifies each
pywbem.WBEMConnectionobject created. The connection id is immutable and is accessible as
pywbem.WBEMConnection.conn_id. It is included in each log record and may be used to relate pywbem log records to connections.
- A standard Python warning that indicates a deprecated functionality.
See section Deprecation and compatibility policy and the standard
- CIM namespace
- A CIM namespace (defined in DSP0004) provides a scope of uniqueness for CIM objects; specifically, the names of class objects and of qualifier type objects shall be unique in a namespace. The compound key of non-embedded instance objects shall also be unique across all non-embedded instances of the class (not including subclasses) within the namespace.
- connections file
A file maintained by pywbemcli and managed by the connection command group. The connections file defines a list of named WBEM connection definitions, each of which is either the set of parameters for connecting to a real WBEM server, or the set of files for creating a mock WBEM server. This allows connection definitions to be persisted and referenced by name in pywbemcli commands, via the --name general option.
By default, the connections file is
.pywbemcli_connections.yamlin the user’s home directory. The user’s home directory depends on the operating system used. It is determined with
os.path.expanduser("~"), which works on all operating systems including Windows. See
expanduser()for details. The default connections file can be changed using the
PYWBEMCLI_CONNECTIONS_FILEenvironment variable, or with the --connections-file general option.
- MOF (Managed Object Format) is the language used by the DMTF to describe in textual form CIM objects including CIM classes, CIM instances, etc. It is one of the output formats provided for the display of CIM objects in pywbemcli. See DMTF DSP0004 for more information on the MOF format.
- WBEM management profile
- management profile
WBEM management profiles define specific management functionality in terms of the CIM model and WBEM operations. The DMTF publishes management profiles in several areas and the SNIA within the SMI-S specification.
Management profiles are identified by organization, name and version. WBEM servers advertise the management profiles that are implemented by the server so that they can be discovered by WBEM clients to determine the management capabilities of the WBEM server. This includes providing the clients a programmatic access to the central instances of the management profile. For details, see Profile advertisement methodologies.
- central instances
- The CIM instances that act as an algorithmic focal point for accessing the management functionality provided by the implementation of a management profile on a WBEM server. The central instances typically represent the central managed resource in the management domain that is addressed by the management profile.
- WBEM URI
- WBEM URI is a standardized text form for CIM object paths and is defined in DSP0207. Pywbemcli uses the untyped WBEM URI format for instance names in the command line (i.e. INSTANCENAME).
- Stands for “Read-Execute-Print-Loop” which is a term that denotes the pywbemcli shell interactive mode where multiple command groups and commands may be executed within the context of a connection defined by a set of general options.
- Unix-style path name pattern
- A pattern used in Unix environments for path names (file names and
directory names). It is used by pywbemcli for example to expand class
names in the
class findcommand. No tilde expansion is done, but
?, and character ranges expressed with
are supported. Example:
- source end role
- The reference in an association class that is on the source side when performing an association traversal. The source side is where the traversal begins.
- far end role
- The reference in an association class that is on the far side when performing an association traversal. The far side is where the traversal ends.
- traditional operations
- The CIM-XML operations originally defined by the DMTF in
(DSP0200) for requesting multiple instances from a WBEM server
ExecQuery. These are monolithic operations and expect the WBEM server to prepare complete responses before returning any results. Because the response must be either contain all of the requested instances or an error response they causes issues with very large reponses. In later versions of (DSP0200), an alternative to the above operations named pull operations were added to improve memory and response efficiency.
- The UNIX-like shells interpret single and double quotes in a certain way and remove them before passing the arguments on to the program invoked. Because the single and double quotes in INSTANCENAME need to be passed on to pywbemcli, they need to be protected from removal by the shell. This can be achieved by putting INSTANCENAME into single quotes if it only includes double quotes, or into double quotes if it only includes single quotes. If there is a mix of single and double quotes in INSTANCENAME, or if shell variables need to be expanded, this can be achieved by backslash-escaping any double quotes in INSTANCENAME, and putting it into double quotes.
- default connection
- A connection definition in the connections file that is used
by pywbemcli as the current connection if pywbemcli is started without
any connection definition (no --server general option,
--mock-server general option, or --name general option) and
the default connection is defined.
A connection definition in the connections file becomes the
default connection on pywbemcli startup if it is specified using the
connection select command and the
-dcommand option is used.
- current connection
- The connection definition in pywbemcli that is currently active; it is the target connection for pywbemcli commands. The current connection is created on pywbemcli startup with the following options --server general option, --mock-server general option, or --name general option or if a default connection) has been defined. The current connection can be changed in the interactive mode with the connection select command.
- CQL (CIM Query Language) is a query language defined by DMTF for use
by query operations against WBEM servers. In operation parameters that
define the use of a query language, it is specified with the string
DMTF:QCL. CQL is described in DMTF standard DSP0202.
4.2. Profile advertisement methodologies¶
This section briefly explains the profile advertisement methodologies defined by DMTF. A full description can be found in DSP1033.
These methodologies describe how a client can discover the central instances of a management profile. Discovering the central instances through a management profile is the recommended approach for clients, over simply enumerating a CIM class of choice. The reason is that this approach enables clients to work seamlessly with different server implementations, even when they have implemented a different set of management profiles.
The DMTF defines three profile advertisement methodologies in DSP1033:
- GetCentralInstances methodology (new in DSP1033 1.1)
- Central class methodology
- Scoping class methodology
At this point, the GetCentralInstances methodology has not widely been implemented, but pywbem supports it nevertheless.
All three profile advertisement methodologies start from the CIM_RegisteredProfile instance that identifies the management profile, by means of registered organization, registered name, and registered version.
It is important to understand that the CIM_RegisteredProfile instance not only identifies the management profile, but represents a particular use of the management profile within its scoping profiles. For an autonomous profile, there are no scoping profiles, so in that case, there is only one use of the autonomous profile in a server. However, component profiles do have scoping profiles, and it is well possible that a component profile is used multiple times in a server, in different scoping contexts. If that is the case, and if discovery of central instances using any of the profile advertisement methodologies is supposed to work, then each such use of the profile needs to have its own separate CIM_RegisteredProfile instance, because each such use of the profile will also have its own separate set of central instances.
Unfortunately, neither the DMTF standards nor the SMI-S standards are clear about that requirement, and so there are plenty of implementations that share a single CIM_RegisteredProfile instance identifying a particular component profile, for multiple distinct uses of the profile by its scoping profiles. In such a case, the profile advertisement methodologies will not be able to distinguish the distinct sets of central instances alone, and other means need to be used to distinguish them.
It is also important to understand that the choice which profile advertisement methodology to implement, is done by the WBEM server side. Therefore, a WBEM client such as pywbem needs to support all methodologies and needs to try them one by one until one succeeds. Pywbem tries the three methodologies in the order listed above.
In the GetCentralInstances methodology, the CIM_RegisteredProfile instance has a CIM method named GetCentralInstances that returns the instance paths of the central instances of the use of the profile.
In the central class methodology, the CIM_RegisteredProfile instance is associated directly with the set of central instances of the use of the profile, via a CIM_ElementConformsToProfile association.
In the scoping class methodology, the CIM_RegisteredProfile instance is not associated directly with the set of central instances of the use of the profile, but delegates that to its scoping profile. The client navigates up to the CIM_RegisteredProfile instance representing the (use of the) scoping profile, looks up its central instances, and from each of those, navigates down along the reversed scoping path to the central instances of the profile in question. The scoping path of a component profile describes the traversal across associations and ordinary classes from the central class to the scoping class of the profile. This profile advertisement methodology is obviously the most complex one of the three.
Pywbem encapsulates the complexity and choice of these methodologies into
a single invocation of an easy-to use method
Profile implementations in a WBEM server are not entirely free when making a choice of which methodology to implement:
Autonomous profiles in a WBEM server must implement the central-class methodology, and may in addition implement the GetCentralInstances methodology.
Note that the scoping class methodology falls together with the central class methodology for autonomous profiles, because their scoping class is also their central class.
Component profiles in a WBEM server may implement the central class methodology and the GetCentralInstances methodology, and must support the scoping class methodology.
Note that implementing the scoping class methodology in a WBEM server requires implementing the classes and associations of the scoping path, which are usually mandatory anyway. So while the scoping class methodology is more complex to use for clients than the central class methodology, it is easier to implement for servers.
Use of the scoping class methodology by a client requires knowing the central class, scoping class and scoping path defined by the component profile.
DSP1001 requires that conformant autonomous profiles specify a central class, and that conformant component profiles specify a central class, scoping class and a scoping path.
Older DMTF component profiles and older SNIA subprofiles do not always specify
scoping class and scoping path. In such cases, the scoping class and scoping
path can often be determined from the class diagram in the specification for
CIM_ComputerSystem is the scoping class.
- DMTF DSP0004, CIM Infrastructure, Version 2.8
- DMTF DSP0200, CIM Operations over HTTP, Version 1.4
- DMTF DSP0201, Representation of CIM in XML, Version 2.4
- DMTF DSP0202, CIM Query Language Specification, Version 1.0
- DMTF DSP0207, WBEM URI Mapping, Version 1.0
- DMTF DSP0212, Filter Query Language, Version 1.0
- DMTF DSP1001, Management Profile Specification Usage Guide, Version 1.1
- DMTF DSP1033, Profile Registration Profile, Version 1.1
- IETF RFC3986, Uniform Resource Identifier (URI): Generic Syntax, January 2005
- IETF RFC6874, Representing IPv6 Zone Identifiers in Address Literals and Uniform Resource Identifiers, February 2013
- WBEM Standards
- DMTF WBEM Standards
- SNIA Storage Management Initiative Specification
- Python Glossary
- A WBEM client and WBEM listener written in Python. See pywbem GitHub repository and the pywbem package on Pypi.