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tpm2_getcap(1) General Commands Manual tpm2_getcap(1)


tpm2_getcap(1) - Display TPM capabilities in a human readable form.


tpm2_getcap [OPTIONS] [CAPABILITY]


tpm2_getcap(1) - Query the TPM for it’s capabilities / properties and print them to the console. It takes a string form of the capability to query as an argument to the tool. Currently supported capability groups are:

algorithms: Display data about supported algorithms.
commands: Display data about supported commands.
pcrs: Display currently allocated PCRs.
properties-fixed: Display fixed TPM properties.
properties-variable: Display variable TPM properties.
ecc-curves: Display data about elliptic curves.
handles-transient: Display handles about transient objects.
handles-persistent: Display handles about persistent objects.
handles-permanent: Display handles about permanent objects.
handles-pcr: Display handles about PCRs.
handles-nv-index: Display handles about NV Indices.
handles-loaded-session: Display handles about both loaded HMAC and policy sessions.
handles-saved-session: Display handles about saved sessions.
vendor[:num]: Displays the vendor properties as a hex buffer output. The string “vendor” can be suffixed with a colon followed by a number as understood by strtoul(3) with a 0 base. That value is used as the property value within the

TPM2_GetCapability command, and defaults to 1. An example to call it with a property value of 2 is: tpm2_getcap vendor:2

NOTE: if vendor requests hang, try the “-i” option to ignore the moreData field and only read once.


-l, --list:

List known supported capability names. These names can be supplied as the argument to the -c option. Output is in a YAML compliant list to stdout.

For example:

- algorithms
- commands
- properties-fixed

Ignores the moreData field when dealing with buggy TPM responses.


This collection of options are common to many programs and provide information that many users may expect.

-h, --help=[man|no-man]: Display the tools manpage. By default, it attempts to invoke the manpager for the tool, however, on failure will output a short tool summary. This is the same behavior if the “man” option argument is specified, however if explicit “man” is requested, the tool will provide errors from man on stderr. If the “no-man” option if specified, or the manpager fails, the short options will be output to stdout.

To successfully use the manpages feature requires the manpages to be installed or on MANPATH, See man(1) for more details.

-v, --version: Display version information for this tool, supported tctis and exit.
-V, --verbose: Increase the information that the tool prints to the console during its execution. When using this option the file and line number are printed.
-Q, --quiet: Silence normal tool output to stdout.
-Z, --enable-errata: Enable the application of errata fixups. Useful if an errata fixup needs to be applied to commands sent to the TPM. Defining the environment TPM2TOOLS_ENABLE_ERRATA is equivalent.
-R, --autoflush: Enable autoflush for transient objects created by the command. If a parent object is loaded from a context file also the transient parent object will be flushed. Autoflush can also be activated if the environment variable TPM2TOOLS_AUTOFLUSH is is set to yes or true.

TCTI Configuration

The TCTI or “Transmission Interface” is the communication mechanism with the TPM. TCTIs can be changed for communication with TPMs across different mediums.

To control the TCTI, the tools respect:

The command line option -T or --tcti
The environment variable: TPM2TOOLS_TCTI.

Note: The command line option always overrides the environment variable.

The current known TCTIs are:

tabrmd - The resource manager, called tabrmd ( Note that tabrmd and abrmd as a tcti name are synonymous.
mssim - Typically used for communicating to the TPM software simulator.
device - Used when talking directly to a TPM device file.
none - Do not initalize a connection with the TPM. Some tools allow for off-tpm options and thus support not using a TCTI. Tools that do not support it will error when attempted to be used without a TCTI connection. Does not support ANY options and MUST BE presented as the exact text of “none”.

The arguments to either the command line option or the environment variable are in the form:


Specifying an empty string for either the <tcti-name> or <tcti-option-config> results in the default being used for that portion respectively.

TCTI Defaults

When a TCTI is not specified, the default TCTI is searched for using dlopen(3) semantics. The tools will search for tabrmd, device and mssim TCTIs IN THAT ORDER and USE THE FIRST ONE FOUND. You can query what TCTI will be chosen as the default by using the -v option to print the version information. The “default-tcti” key-value pair will indicate which of the aforementioned TCTIs is the default.

Custom TCTIs

Any TCTI that implements the dynamic TCTI interface can be loaded. The tools internally use dlopen(3), and the raw tcti-name value is used for the lookup. Thus, this could be a path to the shared library, or a library name as understood by dlopen(3) semantics.


This collection of options are used to configure the various known TCTI modules available:

device: For the device TCTI, the TPM character device file for use by the device TCTI can be specified. The default is /dev/tpm0.

Example: -T device:/dev/tpm0 or export TPM2TOOLS_TCTI=“device:/dev/tpm0”

mssim: For the mssim TCTI, the domain name or IP address and port number used by the simulator can be specified. The default are and 2321.

Example: -T mssim:host=localhost,port=2321 or export TPM2TOOLS_TCTI=“mssim:host=localhost,port=2321”

abrmd: For the abrmd TCTI, the configuration string format is a series of simple key value pairs separated by a `,' character. Each key and value string are separated by a `=' character.
TCTI abrmd supports two keys:
`bus_name' : The name of the tabrmd service on the bus (a string).
`bus_type' : The type of the dbus instance (a string) limited to `session' and `system'.

Specify the tabrmd tcti name and a config string of bus_name=com.example.FooBar:


Specify the default (abrmd) tcti and a config string of bus_type=session:


NOTE: abrmd and tabrmd are synonymous.


To list the fixed properties of the TPM

tpm2_getcap properties-fixed

To list the supported capability groups

tpm2_getcap -l


Tools can return any of the following codes:

0 - Success.
1 - General non-specific error.
2 - Options handling error.
3 - Authentication error.
4 - TCTI related error.
5 - Non supported scheme. Applicable to tpm2_testparams.


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