tar.gz of the same file is different?
Jul 12, 2023
I download stuff from the internet and would like to checksum.
The download script appear to extract itself already.
So I try to archive it back and try to run a simplemd5sum.
But it’s not the same md5 sum !!!Experiment
I download the package flyway
$ ls
flyway-7.7.0
flyway-7.7.0
Then I going to make a tar ball and also zipping with tar command
$ tar -cf flyway-7.7.0.tar flyway-7.7.0
$ tar -cf flyway-7.7.0-2.tar flyway-7.7.0
$ gzip flyway-7.7.0.tar
$ gzip flyway-7.7.0-2.tar
$ md5sum *.gz
9e7df6ead10ba08509c522699f9abb9f flyway-7.7.0-2.tar.gz
4364ea9a31b542c9f93b0ccc6dc93fcd flyway-7.7.0.tar.gz
$ tar -cf flyway-7.7.0-2.tar flyway-7.7.0
$ gzip flyway-7.7.0.tar
$ gzip flyway-7.7.0-2.tar
$ md5sum *.gz
9e7df6ead10ba08509c522699f9abb9f flyway-7.7.0-2.tar.gz
4364ea9a31b542c9f93b0ccc6dc93fcd flyway-7.7.0.tar.gz
This also different !
Reason
I clean up a bit.
$ rm *.gz$ tar -cf flyway-7.7.0.tar flyway-7.7.0
$ tar -cf flyway-7.7.0-2.tar flyway-7.7.0
$ tar -cf flyway-7.7.0-2.tar flyway-7.7.0
I try to gzip it again but this time with -n flag
$ gzip -n flyway-7.7.0.tar
$ gzip -n flyway-7.7.0-2.tar
$ md5sum *.gz
66e04e783300b4297ba18bf263e7c767 flyway-7.7.0-2.tar.gz
66e04e783300b4297ba18bf263e7c767 flyway-7.7.0.tar.gz
$ gzip -n flyway-7.7.0-2.tar
$ md5sum *.gz
66e04e783300b4297ba18bf263e7c767 flyway-7.7.0-2.tar.gz
66e04e783300b4297ba18bf263e7c767 flyway-7.7.0.tar.gz
Here we are. The -n flag is
-n, --no-name
do not save or restore the original name and timestamp
do not save or restore the original name and timestamp
This is because the default option include name and timestamp.
So it make the file sum change !
Hope this help.
Cheers !
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