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I have an automated docker images build where I download elasticsearch archive and extract it via:

tar zxf archive.tar.gz --strip-components=1 -C /path/to/dir

And it always worked until the latest releases (6.8.5 and 7.4.2). It no longer works for 6.8.5, meaning the flag --strip-components no longer has any effect. However, it works fine for 7.4.2. After comparing these two archives the only difference I've found is that 6.8.5 has a different ownership of files in the archive – 631:503 vs root:root in 7.4.2. However, if that was the issue flags --no-same-owner or --user should've resolved the issue by they didn't. I even created a user/group with those IDs and extracted the archive under this user but it also had no effect.

This is how you can reproduce (replace 6.8.5 to 7.4.2 to try both):

$ docker run --rm -ti alpine:3.10.3 sh

### from the container

$ wget https://artifacts.elastic.co/downloads/elasticsearch/elasticsearch-6.8.5.tar.gz
$ apk add --update tar
$ mkdir elastic
$ tar zxvf elasticsearch-6.8.5.tar.gz --strip-components=1 -C elastic
$ ls -la elastic

With 6.8.5 you'll the intermediary directory that wasn't stripped, with 7.4.2 you won't see it despite it exists in both archives.

As you may notice I don't use tar from musl, I used the GNU version from alpine packages (version 1.32) that have been there for a few months already. I use this package with the same flags in many others builds and it works just fine for me.

1 Answer 1

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As was explained to me by Elastic staffer on github this happens due to a leading ./ on the paths within the archive:

/ # tar tvf elasticsearch-6.8.5.tar.gz --numeric-owner | head -n 2
drwxr-xr-x 631/503           0 2019-11-14 14:20 ./
drwxr-xr-x 631/503           0 2019-11-13 20:07 ./elasticsearch-6.8.5/

So, in this case --strip-components should be 2, not 1. To handle this kind of situations universally you can list the archive before extracting and if it has ./ you can dynamically change the --strip-components count:

$ if tar tf elasticsearch-6.8.5.tar.gz | head -n 1 | grep -q '^./$'; then STRIP_COMPONENTS_COUNT=2; else STRIP_COMPONENTS_COUNT=1; fi
$ tar zxvf elasticsearch-6.8.5.tar.gz --strip-components=$STRIP_COMPONENTS_COUNT -C elastic

But, honestly, good archives should be created without any ./ which is super confusing because unless you list files in the archive you won't notice any difference.

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