On your Linux system add a new group called tablet and make sure it uses GID 29999.

Then add your normal Linux desktop user to that group, you should then be able to read/write to any file on the MyDocs / MicroSD partitions (since they're not just user owned by 29999 but also group owned by 29999 and presuming the files are read/write for both user and group you'll be OK).

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Alternatively you may find you already have a 'users' group on your Linux system probably using GID 100, you could change this on your linux system to 29999 or change the 'users' group on the tablet to be 100... but who knows how that might affect the tablet.

Any more thoughts on the most recommended way?