How did you create
sha256sum.sha256? It seems there is a formatting problem 'RT-N16_3.0.0.4_374.43_2-39L3j9527.trx'$'\r': vs. RT-N16_3.0.0.4_374.43_2-39L3j9527.trx. Try to edit or recreate the file with an editor on your Ubuntu system.