[tshaddox]

If you're fond of this rule and want to remember to follow it, just consider how you would write the past tense of the verb.

[richdougherty]

Verb: LOG IN => - they LOGGED IN - the user LOGS IN - when LOGGING IN

Noun: LOGIN => - a LOGIN - some LOGINS

References: https://grammarist.com/spelling/log-in-login/ https://en.wikipedia.org/wiki/Phrasal_verb

[hunter2_]

Similar logic comes into play with mic (noun) and mike (verb). "They miked (or they're miking) the drums with several mics."

We avoid mic (verb) because the "k" works so much better than "c" when leading into various verb endings like -ed and -ing. It's the same reason we add "k" to the word traffic to form words like trafficking; we would interpret the "c" softly ("s" sound) if it was followed by a vowel. But in this case we replace it with "k" instead of adding "k" to maintain the long "i" which would shorten if followed by more than one consonant.

Mic (noun only) is great as a truncation of microphone, though.

[rzzzt]

Login, logan, logun? I kind of like the idea.

[jhardy54]

Nitpick: This works for "logged in", but not "set up".

[chordalkeyboard]

“Set us up the bomb”

[asidiali]

Is setting up?

[jhardy54]

They said "past tense" whereas "setting up" is the present participle tense.