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% tpm2_getrandom(1) tpm2-tools | General Commands Manual
# NAME
**tpm2_getrandom**(1) - Retrieves random bytes from the TPM.
# SYNOPSIS
**tpm2_getrandom** [*OPTIONS*] [*ARGUMENT*]
# DESCRIPTION
**tpm2_getrandom**(1) - Returns the next _SIZE_ octets from the random number
generator. The _SIZE_ parameter is expected as the only argument to the tool.
Note that the TPM specification recommends that TPM's fix the number of
available entry to the maximum size of a hash algorithm output in bytes.
Most TPMs do this, and thus the tool verifies that input size is bounded by
property **TPM2_PT_MAX_DIGEST** and issues an error if it is too large.
Output defaults to *stdout* and binary format unless otherwise specified with
**-o** and **--hex** options respectively.
# OPTIONS
* **-o**, **\--output**=_FILE_
Specifies the filename to output the raw bytes to. Defaults to stdout as a
hex string.
* **\--hex**
Convert the output data to hex format without a leading "0x".
* **-f**, **\--force**
Override checking that the:
- Requested size is within the hash size limit of the TPM.
- Number of retrieved random bytes matches requested amount.
* **-S**, **\--session**=_FILE_:
An HMAC session to be used as an audit session. The session can
be created using **tpm2_startauthsession**.
* **\--cphash**=_FILE_:
File path to record the hash of the command parameters. This is commonly
termed as cpHash. NOTE: When this option is selected, in absence of rphash
option, The tool will not actually execute the command, it simply returns a
cpHash.
* **\--rphash**=_FILE_:
File path to record the hash of the response parameters. This is commonly
termed as rpHash.
* **ARGUMENT** the command line argument specifies the size of the output.
## References
[common options](common/options.md) collection of common options that provide
information many users may expect.
[common tcti options](common/tcti.md) collection of options used to configure
the various known TCTI modules.
# EXAMPLES
## Generate a random 20 bytes and output the binary data to a file
```bash
tpm2_getrandom -o random.out 20
```
## Generate a random 8 bytes and output the hex formatted data to stdout
```bash
tpm2_getrandom 8
```
[returns](common/returns.md)
[footer](common/footer.md)
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