using the filename to get the mimetype is not always correct

Thanks for your bug. That's known upstream:
http://bugzilla.gnome.org/show_bug.cgi?id=166603

Actually, this is not related to the upstream bug. AFAIK file-roller tries to uncompress .Z files using 'uncompress', which is not present. However gzip can handle such files. file-roller should use "gzip" to uncompress these files instead of "uncompress", and use "compress" to compress them.

uncompress is shipped with the gzip package according to dlocate on my dapper installation

You're right. file-roller actually looks for both compress and uncompress, while only the latter exists, even if all we want to do is uncompress. gzip doesn't handle compressing files to .Z format, only uncompressing them.

from src/fr-command-tar.c:

 if ((prog == FR_COMPRESS_PROGRAM_COMPRESS) &&
            ((!is_program_in_path("compress")) ||
             (!is_program_in_path("uncompress")))) {
                return NULL;
        }

/usr/bin/compress is contained in ncompress (from Universe) - we could make file-roller Suggests it.

Does this still not work?

Installation: Ubuntu Gutsy Gibbon, i386.

I want to confirm this bug.

I try to open tar.Z file but the GNOME's file-roller app does not understand the file format.

Trying to download the examples for O'Reilly's "XLib Programming Manual" book
from: http://examples.oreilly.com/v1/

Click on the tar.Z file name and GNOME's file-roller fails.
See this picture: http://www.futuredesktop.org/tmp/File-roller-tar.Z-error.png

Bug still exists in Hardy.

Could we remove the connection to gnome-bug-#126130? The problem isn't that file-roller misidentifies the file, the problem is that it checks for both compress and uncompress, when Ubuntu only includes uncompress by default.

This bug was fixed in the package file-roller - 2.23.6-0ubuntu1

---------------
file-roller (2.23.6-0ubuntu1) intrepid; urgency=low

  * New upstream version:
    Bugs fixed:
    - #350640: sending an empty folder doesn't work. (lp: #55603)
    - #548020: "create archive" directory selection not working correctly.
        (lp: #230044)
    - #546698: file-roller-2.23.1/2.23.5 removes r/x bit for anyone but
               root from / (lp: #250021)
    - #547733: 7-zip tells about invalid command line
    - #547297: Crash reading zip/7za files with 7z version 4.55.
    - #546978: wrong icon for folders.
    - #547017: segfault in "Open with".
    - #546505: Debian packages not supported anymore. (lp: #258499)
    - #542424: Tar.bz2 archives create uncompressed archive files.
    - #546541: Typo and little errors in documentation.
    - LP#26662: file-roller fails to open .Z files. (lp: #26662)
  * debian/file-roller.mime:
    - new version update
  * debian/patches/70_autoconf.patch:
    - new version update

 -- Sebastien Bacher <email address hidden> Tue, 19 Aug 2008 09:37:02 +0200

This bug still exists... try the following:

touch a.b
tar -cf aTarFile a.b

Now you have a "tar"-file. Trying to open it in file-roller will produce an error.

file aTarFile
> aTarFile: POSIX tar archive (GNU)

Renaming the archive to any uncompressable file-type (like *.zip, *.lzma, *.7z, ... or just *.tar) will give you a file which can now be opened by file-roller, even though this is "just" a tar-file.

I know this is an old thread, but this bug still exists in 3.10.2.1 as packaged for ubuntu 14.04 and linux mint 17.

I created a new issue for this: https://gitlab.gnome.org/GNOME/file-roller/issues/2

Although I'm not sure this issue and the new issue are related.

Marked as fix released because the original issue is fixed.