Uncompressed file estimation wrong?

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I had a large (~60G) compressed file (tar.gz).



I used split to break it into 4 parts and then cat to join them back together.



However, now, when I am trying to estimate the size of the uncompressed file, it turns out it is smaller than the original? How is this possible?



$ gzip -l myfile.tar.gz 
 compressed uncompressed ratio uncompressed_name
 60680003101 3985780736 -1422.4% myfile.tar





tar compression split







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    up vote
    1
    down vote

    favorite












    I had a large (~60G) compressed file (tar.gz).



    I used split to break it into 4 parts and then cat to join them back together.



    However, now, when I am trying to estimate the size of the uncompressed file, it turns out it is smaller than the original? How is this possible?



    $ gzip -l myfile.tar.gz 
     compressed uncompressed ratio uncompressed_name
     60680003101 3985780736 -1422.4% myfile.tar





    tar compression split







    share|improve this question























      up vote
      1
      down vote

      favorite









      up vote
      1
      down vote

      favorite











      I had a large (~60G) compressed file (tar.gz).



      I used split to break it into 4 parts and then cat to join them back together.



      However, now, when I am trying to estimate the size of the uncompressed file, it turns out it is smaller than the original? How is this possible?



      $ gzip -l myfile.tar.gz 
       compressed uncompressed ratio uncompressed_name
       60680003101 3985780736 -1422.4% myfile.tar





      tar compression split







      share|improve this question













      I had a large (~60G) compressed file (tar.gz).



      I used split to break it into 4 parts and then cat to join them back together.



      However, now, when I am trying to estimate the size of the uncompressed file, it turns out it is smaller than the original? How is this possible?



      $ gzip -l myfile.tar.gz 
       compressed uncompressed ratio uncompressed_name
       60680003101 3985780736 -1422.4% myfile.tar





      tar compression split




      tar compression split






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked 1 hour ago









      pkaramol

      345112




      345112




















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          This is caused by the size of the field used to store the uncompressed size in gzipped files: it’s only 32 bits, so gzip can only store sizes of files up to 4 GiB. Anything larger is compressed and uncompressed correctly, but gzip -l gives an incorrect uncompressed size.



          So splitting the tarball and reconstructing it hasn’t caused this, and shouldn’t have affected the file — if you want to make sure, you can check it with gzip -tv.



          See Fastest way of working out uncompressed size of large GZIPPED file for more details, and the gzip manual:




          The gzip format represents the input size modulo 2³², so the uncompressed size and compression ratio are listed incorrectly for uncompressed files 4 GiB and larger.







          share|improve this answer






















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            1 Answer
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            1 Answer
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            up vote
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            accepted










            This is caused by the size of the field used to store the uncompressed size in gzipped files: it’s only 32 bits, so gzip can only store sizes of files up to 4 GiB. Anything larger is compressed and uncompressed correctly, but gzip -l gives an incorrect uncompressed size.



            So splitting the tarball and reconstructing it hasn’t caused this, and shouldn’t have affected the file — if you want to make sure, you can check it with gzip -tv.



            See Fastest way of working out uncompressed size of large GZIPPED file for more details, and the gzip manual:




            The gzip format represents the input size modulo 2³², so the uncompressed size and compression ratio are listed incorrectly for uncompressed files 4 GiB and larger.







            share|improve this answer


























              up vote
              4
              down vote



              accepted










              This is caused by the size of the field used to store the uncompressed size in gzipped files: it’s only 32 bits, so gzip can only store sizes of files up to 4 GiB. Anything larger is compressed and uncompressed correctly, but gzip -l gives an incorrect uncompressed size.



              So splitting the tarball and reconstructing it hasn’t caused this, and shouldn’t have affected the file — if you want to make sure, you can check it with gzip -tv.



              See Fastest way of working out uncompressed size of large GZIPPED file for more details, and the gzip manual:




              The gzip format represents the input size modulo 2³², so the uncompressed size and compression ratio are listed incorrectly for uncompressed files 4 GiB and larger.







              share|improve this answer
























                up vote
                4
                down vote



                accepted







                up vote
                4
                down vote



                accepted






                This is caused by the size of the field used to store the uncompressed size in gzipped files: it’s only 32 bits, so gzip can only store sizes of files up to 4 GiB. Anything larger is compressed and uncompressed correctly, but gzip -l gives an incorrect uncompressed size.



                So splitting the tarball and reconstructing it hasn’t caused this, and shouldn’t have affected the file — if you want to make sure, you can check it with gzip -tv.



                See Fastest way of working out uncompressed size of large GZIPPED file for more details, and the gzip manual:




                The gzip format represents the input size modulo 2³², so the uncompressed size and compression ratio are listed incorrectly for uncompressed files 4 GiB and larger.







                share|improve this answer














                This is caused by the size of the field used to store the uncompressed size in gzipped files: it’s only 32 bits, so gzip can only store sizes of files up to 4 GiB. Anything larger is compressed and uncompressed correctly, but gzip -l gives an incorrect uncompressed size.



                So splitting the tarball and reconstructing it hasn’t caused this, and shouldn’t have affected the file — if you want to make sure, you can check it with gzip -tv.



                See Fastest way of working out uncompressed size of large GZIPPED file for more details, and the gzip manual:




                The gzip format represents the input size modulo 2³², so the uncompressed size and compression ratio are listed incorrectly for uncompressed files 4 GiB and larger.








                share|improve this answer














                share|improve this answer



                share|improve this answer








                edited 47 mins ago

























                answered 56 mins ago









                Stephen Kitt

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