particle N1 uncommon writtenliterary
ただ〜のみだ — all one can do is ~
ただ〜のみだ ・ ただのみだ
A full written guide for ただ〜のみだ is on the way.
This point is mapped in the grammar tree, but its examples, formation table and usage notes haven't been written yet. The fastest way to learn it now is to meet it in real sentences inside Jengo.
See ただ〜のみだ in real sentences
Jengo shows ただ〜のみだ the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.
Study it in JengoSources Compiled from published Japanese grammar references.