The options -Z, --compress, and --uncompress all require that there be a 'compress' utility installed on the system. If there is no compress installed on your system, you will get errors if you try to use these options to tar. While the algorithm used by compress was originally encumbered by patents, enough time has passed that 'ncompress' is now available in Debian main. - - - - - The tar upstream developers prefer to document using the 'info' format, but unfortunately the info docs are under a license Debian considers non-free. If you want the full, canonical documentation for tar and not just the man page that upstream provides as a courtesy to users, you might want to install the tar-doc package which can be found in Debian non-free. Alternatively, you can find the tar doc online at https://www.gnu.org/software/tar/manual/