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This a matter of file owner's permissions. If the file was not created under the same user-id as the one you are using for reading, permissions for group or "others" are in effect depending on the current group-id.

During your upgrade, the user-ids and group-ids may have changed if you created them in a different order. The numeric encoding for the initial ones remained on the disc, resulting in the conflict you experienced.

Your options is either to restore the old id's or to re-own the files.

  • restore old id's

If there is no corresponding user and and group for UID and GID, command ls -l will list numeric UID and GID. Then you can reassign those id's to your user-id (under root mode) with (adapt to your configuration)

   usermod -u 999 mynewuser` and `groupmod -g 999 mynewgroup
  • re-own files

    • if you happen to known your old UID and GID, you can do a system-wide operation with

      find / -group 999 -exec chgrp -h mynewgroup {} \;
      find / -user 999 -exec chown -h mynewuser {} \;
    • otherwise, you must process each directory manually with chown and chgrp commands

Use man <command> for details.

In the simplest case, when UID and GID are correct, you may solve the issue by changing permissions on the files with chmod o+rw g+rw o=r <file-name>.

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