P.S. However, there is a caveat on that rule in Japan. In Japan, the law allows manufacturers to revoke the warranty if the preinstalled OS was changed. I.e. even Windows upgrade on Sony laptops may nullify the warranty in Japan (the company may use that trick for evading responsibility).

AFAIK(i.e. I may be mistaken, which is not very probable), there are no restrictions from DELL on installing any OS you like. Dell just not supports any drivers, and not guarantees hardware compatibility with an OS not officially shipped by DELL with that model. Obviously, when returning for repair, you should try putting back the OS shipped originally.

https://www.dell.com/support/home/en-us/drivers/supportedos/precision-t5400

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@Andy812 wrote:

P.S. However, there is a caveat on that rule in Japan. In Japan, the law allows manufacturers to revoke the warranty if the preinstalled OS was changed. I.e. even Windows upgrade on Sony laptops may nullify the warranty in Japan (the company may use that trick for evading responsibility).

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I didn't know about this trick...