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#### 8.3.6 GNU and old GNU `tar` format

GNU `tar` was based on an early draft of the POSIX 1003.1 `ustar` standard. GNU extensions to `tar`, such as the support for file names longer than 100 characters, use portions of the `tar` header record which were specified in that POSIX draft as unused. Subsequent changes in POSIX have allocated the same parts of the header record for other purposes. As a result, GNU `tar` format is incompatible with the current POSIX specification, and with `tar` programs that follow it.

In the majority of cases, `tar` will be configured to create this format by default. This will change in future releases, since we plan to make ‘`POSIX`’ format the default.

To force creation a GNU `tar` archive, use option `--format=gnu`.