The following script

mkdir test && cd test
mkdir files
touch files/{1,2,3}
tar --create --file "test.lzma" files/{1,2,3} --auto-compress
mkdir extracted_files
tar --extract --file "test.lzma" --directory extracted_files --auto-compress

produces the following error:

tar: This does not look like a tar archive

but actually tar+compress and uncompress+untar do happen (files are in place). Why is this happening? Is it some kind of bug in tar?

On my system:

xz --version
 xz (XZ Utils) 5.2.7
 liblzma 5.2.7
tar --version
 tar (GNU tar) 1.34
file test/test.lzma
 test/test.lzma: LZMA compressed data, streamed
ls test/extracted_files/

You can also reproduce it in https://replit.com/languages/bash (with xz (XZ Utils) 5.2.2 and tar (GNU tar) 1.34). But not in https://www.onlinegdb.com/online_bash_shell (with xz (XZ Utils) 5.2.4 and tar (GNU tar) 1.30).

  • 1
    here with XZ 5.2.5 and tar 1.34 the .lzma file format is XZ instead of LZMA and "it works". So I can reproduce it instead by using -Ilzma instead of --auto-compress at creation time. Then it fails at extraction time with --auto-compress. Of course it works if I force -Ilzma at extraction time. (note: lzma is an alias of xz with changed behavior).
    – A.B
    Oct 21, 2022 at 14:58

1 Answer 1


Fixed in upstream. Check out https://savannah.gnu.org/bugs/index.php?63250.

@Sergey Poznyakoff <gray>:

The "This does not look like a tar archive" is not an error, but a warning. It is produced, in particular, when tar is unable to determine file format by signature and file size is less than tar block size. When the signature recognition fails, tar tries to determine file format by its suffix. In this case, it succeeded and extracted the files.

I have installed the following fix to recognized LZMA files produced by xz:


PS: The --auto-compress option is not needed when extracting.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .