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I have here a POSIX tar archive call Debian9.ova.

Interestingly enough, listing it with tar in MacOS High Sierra, shows:

$ tar -tvf Debian9.ova 
-rw-r--r--  0 someone someone  5344 26 Feb 13:57 Debian9.ovf
-rw-r--r--  0 someone someone   179 26 Feb 13:57 Debian9.mf
-rw-r--r--  0 someone someone 2113245184 26 Feb 13:59 Debian9-disk1.vmdk

Now the interesting point is, that I do not have a someone user and group.

$ id someone
id: someone: no such user

Listing it with --numeric-owner, it shows as uid 64, and gid 64, which clearly are not present in my system.

$ tar -tvf Debian9.ova --numeric-owner
-rw-r--r--  0 64     64       5344 26 Feb 13:57 Debian9.ovf
-rw-r--r--  0 64     64        179 26 Feb 13:57 Debian9.mf
-rw-r--r--  0 64     64 2113245184 26 Feb 13:59 Debian9-disk1.vmdk

Listing the users in the system does not find a somebody user:

dscl . list  /Users | grep someone

Where is then someone coming from? Is it a tar "feature" when it finds an unknown uid and gid?

PS. In debian just for comparison:

$ tar -tvf a.tar
-rw-r--r-- 64/64          3212 2018-02-27 02:01 dead.letter
$ bsdtar -tvf a.tar
-rw-r--r--  0 64     64       3212 Feb 27 02:01 dead.letter
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I have here a POSIX tar archive […]

In a standard format tar archive, the header information for each file contains fields for both a symbolic user and group name and a numeric user and group ID.

As you have seen, tar can list either one set of fields or the other.

With a conformant pax utility one should be able to list these fields altogether:

$ pax -o listopt="%(uid)s %(gid)s %(uname)s %(gname)s %L\n" < Debian9.ova

However, I believe that no standard-conformant pax utility currently exists.

Further reading

  • "ustar header block". pax. Single Unix Specification. IEEE 1003.1-2008:2016.
  • Tim Kientzle (2016-12-27). tar. § 5. FreeBSD File Formats Manual.
  • A conforming pax implementation dumps core with your proposed command line. Use listopt="%(uid)d %(gid)d %(uname)s %(gname)s %L\n" on Solaris, AIX, HP-UX and it will work. – schily May 31 '18 at 10:05

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