option on the command line increases the verbosity level by one.  The maximum verbosity level is 3.  For a detailed discussion of how various verbosity
              levels affect tar’s output, please refer to GNU Tar Manual, subsection 2.5.1 "The --verbose Option".

       --warning=KEYWORD
              Enable or disable warning messages identified by KEYWORD.  The messages are suppressed if KEYWORD is prefixed with no- and enabled otherwise.

              Multiple --warning messages accumulate.

              Keywords controlling general tar operation:

              all    Enable all warning messages.  This is the default.

              none   Disable all warning messages.

              filename‐with‐nuls
                     "%s: file name read contains nul character"

              alone‐zero‐block
                     "A lone zero block at %s"

              Keywords applicable for tar ‐‐create:

              cachedir
                     "%s: contains a cache directory tag %s; %s"

              file‐shrank
                     "%s: File shrank by %s bytes; padding with zeros"

              xdev   "%s: file is on a different filesystem; not dumped"

              file‐ignored
                     "%s: Unknown file type; file ignored"
                     "%s: socket ignored"
                     "%s: door ignored"

              file‐unchanged
                     "%s: file is unchanged; not dumped"

              ignore‐archive
                     "%s: file is the archive; not dumped"

              file‐removed
                     "%s: File removed before we read it"

              file‐changed
                     "%s: file changed as we read it"

              failed‐read
                     Suppresses warnings about unreadable files or directories. This keyword applies only if used together with the --ignore-failed-read option.

              Keywords applicable for tar ‐‐extract:

              existing-file
                     "%s: skipping existing file"

              timestamp
                     "%s: implausibly old time stamp %s"
                     "%s: time stamp %s is %s s in the future"

              contiguous‐cast
                     "Extracting contiguous files as regular files"

              symlink‐cast
                     "Attempting extraction of symbolic links as hard links"

              unknown‐cast
                     "%s: Unknown file type ’%c’, extracted as normal file"

              ignore‐newer
                     "Current %s is newer or same age"

              unknown‐keyword
                     "Ignoring unknown extended header keyword ’%s’"

              decompress‐program
                     Controls verbose description of failures occurring when trying to run alternative decompressor programs.  This warning is disabled by default (unless --verbose is used).  A common example of what you can
                     get when using this warning is:

                     $ tar ‐‐warning=decompress‐program ‐x ‐f archive.Z
                     tar (child): cannot run compress: No such file or directory
                     tar (child): trying gzip

                     This means that tar first tried to decompress archive.Z using compress, and, when that failed, switched to gzip.