bash$ gunzip boot.fs.gz

gunzip: boot.fs.gz: not in gzip format

bash$ unzip boot.fs.gz
Archive:  boot.fs.gz
  End-of-central-directory signature not found.  Either this file is not

  a zipfile, or it constitutes one disk of a multi-part archive.  In the

  latter case the central directory and zipfile comment will be found on

  the last disk(s) of this archive.
unzip:  cannot find zipfile directory in one of boot.fs.gz or
        boot.fs.gz.zip, and cannot find boot.fs.gz.ZIP, period.

bash$ mv boot.fs.gz bootfs.gz
bash$ unzip bootfs.gz
Archive:  bootfs.gz
  End-of-central-directory signature not found.  Either this file is not

  a zipfile, or it constitutes one disk of a multi-part archive.  In the

  latter case the central directory and zipfile comment will be found on

  the last disk(s) of this archive.
unzip:  cannot find zipfile directory in one of bootfs.gz or
        bootfs.gz.zip, and cannot find bootfs.gz.ZIP, period.
bash$ gunzip bootfs.gz

gunzip: bootfs.gz: not in gzip format

gzcat: bootfs.gz: not in gzip format